Chapter 16. invasive Pests—insects and Diseases

457chAPTeR 16. Invasive Pests—Insects and Diseases

DonaldA.DuerrandPaulA.Mistretta1

key FiNDiNGS

•NonnativepestspecieshaveincreasingimpactsintheSouthregardlessofclimatechange,patternsoflandownership,orchangesinthecompositionofvegetation.

• “New”nonnativeinvasiveinsectsanddiseaseswillhaveseriousimpactsonsouthernforestsoverthenext50years.Somespeciessuchasemeraldashborer,laurelwilt,andthousandcankersdiseaseareexpandingrapidly;theythreatentheecologicalviabilityoftheirhoststhroughoutlargeareasoftheSouth.

•Giventhetrendinintroductionsofnonnativeinsectpestsandplantpathogensoverthelast100years,wecanexpectadditionalintroductionsofpreviouslyundocumentedpests(insects,fungalpathogens,plantparasiticnematodes,etc.)fromforeigncountriesthatwillhaveseriousconsequencesforsomenativeforestplantspecies.

•Whenhostmaterialforagiveninsectordiseaseisprojectedtoincreaseoverthenext50yearsasaresultofclimatechangeormanagementchoice,wecanexpectmorepestactivity;forexample,morepineacreageenablesmoresouthernpinebeetledamage.Conversely,ifhostmaterialdecreases,theoverallimpactofpestsutilizingthathostmaterialwilllikelydecrease.

•Veryfewindisputableprojectionscanbemadeabouttheeffectsofclimatechangeonnativeornaturalizedpests.Althoughclimate-change-inducedhostabundanceisexpectedtoincreasetheactivityofsomepests,others(suchasgypsymoth)maybecomelessactivewithwarmertemperaturesdespiterelativelysimilarlevelsofhostavailability.

•Thescientificliteratureandthebodyofexpertopinionareinconclusiveinpredictingtheeffectsofclimatechangeonmanypests’activitylevels,oftenevenlackinghistorictrenddata.However,basedonanecdotalreportsfromprofessionals,andintheabsenceofotherdata,wegenerallyassumethatpestactivitylevelsoverthenext50yearswillbesimilartothepast50yearswithrespecttoimpactonpreferredhosts.

1DonaldA.DuerristheStaffEntomologistandPaulA.MistrettaisaStaffPathologistandRegionalPesticideSpecialist,SouthernRegion,U.S.DepartmentofAgricultureForestService,Atlanta,GA30309.

•Asignificantsourceofuncertaintyinprojectingpestimpactsistheadequacyofpreventionandsuppressionmethods:howeffectiveareexistingmethods,comparedwiththosethatmightbeavailableinthefuture;howwillingandablearelandmanagersorlandownerstoadoptmanagement/controlmethods;howmuchfundingisavailablecomparedtotheamountneededforimplementation.

•Undertheinfluenceofclimatewarminghostplants,pestsandpestcomplexesareexpectedtomigratenorthwardandtohigherelevations.Becausemigrationratesdifferamongtheaffectedspecies,migratingplantsareexpectedtoformnewassociations,whichwillthenaffectthepests,theirhostpopulations,andtheinteractionsamongthem.Unexpectedpestsverylikelywillbecomeimportant,whilesomethatarecurrentlyactivewillbelesssevereintheirnewhabitats.Ashostplants“migrate”tothenorthanincreaseintheincidenceofdeclinesyndromeofplantsintheirpreviousrangeisexpected.

•Althoughnotexpectedtobeasignificantprobleminthenext50years,themigrationoflowerelevationplantstohigherelevationscouldultimatelyeliminateoratleastseverelyrestrictthehostrangesofcurrenthighelevationplantassociations.Peststhatactonarestrictedhostbase,suchasthebalsamwoollyadelgidandbutternutcanker,couldbecomefarmoresignificantecologicallyinareasofrelicthostpopulations.

•Climatechangewillleadtoextrauncertaintyindecisionmaking,especiallyinareaswherethechangescauseincreasedvariabilityinlocal(fragmented)climateregimesthatexceedhistoricalvariabilityoflocalweatherpatterns.

iNTRoDucTioN

Animportantpartofthesouthernforestedlandscapeisthearrayofinsectanddiseasepeststhatsignificantlyaffectthemanagementofforestresourcesonarelativelybroadscale.Thelistof21keypeststhatweredocumentedlessthanadecadeago(WardandMistretta2002)hasalreadyexpandedto30.

Thegoalofthischapteristoprojectthebehaviorofinsectanddiseasepeststhatweanticipatewillaffectforestresourcesoverthenext50years,basedonchangingclimate,

Chapter 16. invasive Pests—insects and Diseases

458The Southern Forest Futures Project

humanactivity,andbiologicfactors.Ourprimaryfocusisonclimatechangeanditssub-elementsoftemperaturerégime(dominatedbytemperatureextremes),overallpatternofsolarradiation,andrainfallpattern.Allavailableclimatechangescenariospredictanenvironmentinwhichweexpectvegetationchangestooccur(Iversonandothers1999).Concurrentwithecologicalchangeswillbeashiftinthepeststhatfunctionwithinanalteredvegetativelandscapeunderchangedtemperature,rainfall,andotherclimaticconditions.Theimpactsonpestactivity,inturn,mayinfluencethedirectionorscopeofotherchangesinforesttypeandstructure.

Thefocusofthischapteristhe30speciesofpestinsectsorfungalpathogensthatcausediseasesprojectedtobeoffutureconcern,withemphasisonthefollowingkeyissues:

•Thehistoricalandforecastedfuturespreadofhighthreatinsectsanddiseases

•Otherpestsinvadingsouthernforestsandotherhighthreatspeciespoisedtoentertheregion

•Expectedconsequencesofthespreadofhigh-threatpestspeciesforforestproductivity,ecosystemcompositionandbiodiversity,threatenedandendangeredspeciesandtheirhabitats,watershedandsoilhealth,carbonstorage,andfiredynamics

• Potentialseverityofpestspeciesthreatsrelativetootherthreatsandtofutureforestsustainability

•Forestspeciesorpopulationsthatarelikelytobelostordramaticallydegradedbypests;theresultingchangesinthecompositionofsouthernforestsoverthenext50years;andthedegreeofcertaintyintheseoutcomes

•Adaptivestrategiesandmethodsforinvasivepestmanagementthatcouldmitigatetheeffectsofpredictedfutureoutbreaks

meThoDS

Inresponsetotheissuesdevelopedabove,wepresentabriefextractofrelevantinformationaboutthepeststhatarewellestablishedinsouthernforests(WardandMistretta2002);weaddmoredetaileddescriptionsofseveralnewpestsorpestcomplexesthathaveemergedinthepastfewyears;weapplytheresultsofpastresearchonpestsandpestmanagementtoexpectedchangesinsouthernforestsoverthenext50years;weidentifymanagementstrategiesforrespondingtopestsinachangingenvironment;andweidentifyresearchneededtoimproveourknowledgeaboutpestswiththeirhostsandtheirinteractionswiththeirchangingenvironment,therebyenablingamorequantitativeapproachtoforecastinginthefuture.

DATA SouRceS

Informationforthischapterisderivedfromtwoprimarysources,selecteditemsfromtheextensivebodyofpublishedscientificliterature,andtheexperienceoftheauthorsandtheircolleaguesinStateandFederalagencies,universities,andotherpublicorprivateorganizationsthatareengagedeitherinresearchorfield-basedpestmanagementactivities.AdditionalinformationaboutforestpestsandtheircontrolisreadilyavailablefromStateandFederalforestryagenciesorontheInternet(twogoodstartingpointsarehttp://fhpr8.srs.fs.fed.us/andhttp://www.na.fs.fed.us/spfo/pubs/fth_pub_pages/fidl.htm).Also,appendixCcontainsadditionalresources(References)notcitedherebutwhichprovidevaluableadditionalbackgroundforunderstandingthebiologyandecologyofthepestsdiscussed.

ReSulTS

ThescientificliteratureonclimatechangeandotherenvironmentalconsiderationsissummarizedinappendixC,whichalsoprovidesthebackgroundinformationonourapproachtopestmodelingandfutureprojectionofimpacts.BelowweaddressthepestsprojectedtoinfluencetheforestsoftheSouthoverthenext50years,theirpotentialdamage,potentiallyeffectivemanagementstrategies,andresearchneededtobetterunderstandandmanagethem(table16.1).

Ofthe30forestpestsintheSouthdiscussedbelow,21arewellestablishedand9arerelativenewcomers.Pestsareroughlyevenlydividedbetweenthoseaffectingsoftwoodsandthoseaffectinghardwoods.

insect Pests of Softwoods

Balsam woolly adelgid—Impactsofbalsamwoollyadelgid,Adelgespiceae,werefirstdocumentedin1957onFraserfirintheSouthernAppalachians.Thefivemajorareasofhigh-elevation,spruce-firforestinNorthCarolina,Tennessee,andVirginiaarehighlyvaluedfortheirscenicandrecreationvalues,attractingseveralmillionvisitorsannually(WardandMistretta2002).Inaddition,severalspeciesoffloraandfaunarelyonmaturespruce-firhabitatforsurvival,andmanyarefoundonlyinthisenvironment.ThebalsamwoollyadelgidhasinfestedFraserfirinallfiveareas.Damagecausedbytheadelgidhasdegradedsceneryandrecreationvalueandputthishabitatofdependanttreespeciesatgreatrisk.


Table 16.1—Important insect and disease pests of southern forests

Pest Pest’s scientific name

Type of pests / abiotic factors origin

Forest type or species affected

Annosum root disease Heterobasidion annosum Fungus Native Pines in the loblolly-shortleaf and longleaf–slash forest types

Asian longhorned beetle Anoplophora glabripennis Insect China Most hardwoods, but especially maples.

Baldcypress leafroller Archips goyerana Insect Native Baldcypress in oak-gum-cypress forest type

Balsam woolly adelgid Adelges piceae Insect Europe Fraser fir in the spruce-fir forest type

Bark beetles (other than southern pine beetle)

Ips avulsus, I. calligraphus, I. grandicolli, & Dendructonus terebrans

Insect Native Pine in the loblolly-shortleaf and longleaf–slash forest types

Beech bark disease Nectria coccinea var. faginata, N. galligena (fungi); 2 (at least) insect vectors

Complex of insects and fungi

Unknown American beech in the oak-hickory forest type

Brown spot needle disease

Scirrhia acicola Fungus Native Longleaf pine in the longleaf–slash forest type

Butternut canker Sirococcus clavigignenti-juglandacearam

Fungus Unknown Butternut in the oak-hickory forest type

Chestnut blight Cryphonectria parasitica Fungus Asia American chestnut, chinquapins, several species of oak in the oak-hickory forest type

Dogwood anthracnose Discula destructiva Fungus Unknown Dogwood in the oak-hickory forest type

Dutch elm disease Ophiostoma ulmi (formerly called Ceratocystis ulmi) & Ophiostoma novo-ulmi (fungi); two bark beetles

Complex of fungi and insects

Europe All elm species

Emerald ash borer Agrilus planipennis Insect Asia All ash species

Forest tent caterpillar Malacosoma disstria Insect Native Hardwoods in the oak-gum-cypress forest type

Fusiform rust Cronartium fusiforme f. sp. fusiforme

Fungus Native Loblolly and slash pines in the loblolly-shortleaf and longleaf slash types

Gypsy moth Lymantria dispar Insect Europe and Asia

Hardwoods (all types)

(Continued)


Table 16.1—(continued) Important insect and disease pests of southern forests

Pest Pest’s scientific name

Type of pests / abiotic factors origin

Forest type or species affected

Hardwood borers Various Insect Native All species of hardwoods

Hemlock woolly adelgid Adelges tsugae Insect Asia Hemlocks

Laurel wilt Raffiella lauricola (fungus), Xyleborus glabratus (insect)

Complex of an insect and fungus

Asia Lauraceae, especially Redbay

Littleleaf disease Phytophthora cinnamomi, Pythium sp.

Tree decline complex; fungi and site factors

Southeast Asia (likely)

Shortleaf and loblolly pines in the loblolly-shortleaf forest type

Loblolly pine decline As a minimum: various fungi (Lophodermium spp.) and insects (Hylastes spp.)

Tree decline complex; insect and fungi

Unknown Pines

Nantucket pine tip moth Rhyacionia frustrana Insect Native Pines

Oak decline Armillaria sp., and other secondary fungi

Tree decline complex; site conditions and fungi

Mixed Oaks

Oak wilt Ceratocystis fagacearum Fungus Native Oaks in the oak-hickory forest type

Pine reproduction weevils Hylobius pales, Pachylobius picivorus

Insect Native Pines

Sirex woodwasp Sirex noctilio (insect), Amylostereum areolatum (fungus)


Europe, Asia, northern Africa

Pines

Soapberry borer Agrilus prionurus Insect Mexico Western soapberry

Southern pine beetle Dendroctonus frontalis Insect Native Pines

Sudden oak death Phytophthora ramorum Fungus Unknown Oaks

Texas leafcutting ant Atta texana Insect Central and South America

Pine (reproduction)

Thousand cankers disease

Geosmithia sp. (fungus), Pityophthorus juglandis (insect)


Unknown Black walnut


hemlocktoserveascoverandnestinghabitatforbirdsandsmallmammals.

Giventheadelgid’scurrentrateofspread,itcouldinfestnearlytheentiresouthernrangeofeasternhemlockandCarolinahemlockwithinthenext50years.Someisolatedareaswithintheinfestedrangeandsomeareasofhemlocksthatareseparatedfromthemainrange(innorthwesternAlabama,forexample)mayescapeinfestation.Inalllikelihood,withinthenext50yearshemlockwoollyadelgidwillkillmostofthehemlocksthatarealivetodayintheSouth.ThelossofhemlockwillbeoneofthemajorimpactscausedbynonnativeinvasivespeciestoSouthernforestsinthenext50years.

Anumberofsuppressiontacticsshowsomepromiseforpreventingthelossofsignificantnumbersofhemlocksoverthenext50years.Treatmentoftreeswithimidacloprideffectivelycontrolshemlockwoollyadelgidsforseveralyears(Cowlesandothers2006).Distributionoftheinsecticideintotreecrownsismoreeffectivewithsoildrenchorinjectionthanwithsteminjection(Dillingandothers2010).Dinotefuranisalsobeingusedwithsuccess.Currentinsecticidetreatmentsareappliedtoindividualtreesandfunctionprimarilyasatemporaryprotectionmeasureforarelativelysmallnumberoftrees.Atthistime,insecticideapplicationoverlargeareasisneitherlogisticallyfeasiblenorcost-effective.Severalbiologicalcontrolagents(beetlepredators)havebeenandarebeingreleased,andsomearesuccessfullyestablishing(Mauselandothers2010).Moretimeislikelyneededbeforeconclusiveimpactsofbiologicalcontrolagentsonthehealthofhemlockforestscanbeshown.Establishmentofacomplexofnaturalenemiesinagivenareaisdesiredtoachievelong-termsuccess.InJune2009,researchersandforesthealthprofessionalsbeganevaluatingtheefficacyofLecanicilliummuscarium,aninsect-killingfungusthatisregisteredasabio-pesticideinEurope(Grassano2008).

Researchandworkisbeingdoneonhemlockhostresistanceandex-situconservationofhemlockseedlingsandgeneticdiversity(Bentzandothers2002,Jettonandothers2008,Jettonandothers2010,Montgomeryandothers2009,Poolerandothers2002).Theseeffortsmayallowscientistsandlandmanagerstoreintroduceadelgid-resistanthemlocksinthefuture.

Climatechangeisunlikelytoreversethespreadofhemlockwoollyadelgids.Inthenorthernpartofthehemlockwoollyadelgidrange,lowminimumwintertemperaturescansignificantlyknockbackpopulationsandappeartolimitspread.Therefore,wecanassumethatclimatewarmingwouldlikelypromoteanorthwardexpansionoftheadelgid(Paradisandothers2008).Thesouthernrangeofhemlockiscurrentlynotbenefittingfrommuchcoldwinter

knockback—awarmingclimatewouldpresumablyonlyexacerbatethesituation.

Nantucket pine tip moth—TheNantucketpinetipmoth,Rhyacioniafrustrana,isoneofthemostcommonforestinsectsintheSouth(Berisford1988).Althoughitisusuallyconsideredasouthernpest,itsrangeincludesmostoftheeasternhalfoftheUnitedStates.

MostcommercialpinespeciesaresusceptibletoattackbytheNantucketpinetipmoth,butthereareconsiderabledifferencesinrelativesusceptibility.Amongthesouthernpines,longleafnurseryseedlingsandallagesofshortleaf,loblolly,andVirginiapinesarehighlysusceptible,whileslashandolderlongleafpinesarehighlyresistant.

Damageisnormallytransitoryornegligibleinforeststandsbutcanbesevereforseedlingsandsaplingsyoungerthan5years,resultingindeformitiesandlossofgrowth.

Basedonthewarmerandpossiblydrierclimatethatisexpectedoverthenext50years,theactivityanddamagelevelsofNantucketpinetipmotharelikelytoincreaseintheSouthandextendtonorthernareas(Midwest,NewEngland)wheretipmothhasnotbeenmuchofamanagementconcern.Activitymayincreaseandcontinueintothewintermonths,ascouldthenumberofgenerationsperyear.Nantucketpinetipmothsareprimarilyaprobleminyoungloblollymonocultures.Totheextentthatlandmanagersincreasetheplantingofloblollymonoculturesinthenext50years,damagefromtheNantucketpinetipmothislikelytoincrease.

Anumberofeffective,chemicalcontroloptionsexistforthispest(Asaroandothers2003).Ifpopulationlevelsaremonitoredinatimelyandregularfashion,andarefollowedupbyappropriateinsecticideapplications,tipmothdamagecanbeminimized.Chemicalcontroloptionsareeffective,especiallythenewsystemicinsecticides.However,theyareoftenprohibitivelyexpensiveandwillprobablynotbeadoptedundermostcommonlyacceptedclimatescenariosunlesstipmothpopulationpressurebecomesquitehigh.

Other bark beetles—Althoughthesouthernpinebeetleisthemostdamaginginsectinsouthernpineforests,itisonlyoneoffivepinebark-beetlespeciesofconcernforforestmanagersintheSouth.Theothersarethesix-spinedengraver,Ipscalligraphus,thesouthernpineengraver,Ipsgrandicollis,thesmallsouthernpineengraver,Ipsavulsus,andtheblackturpentinebeetle,Dendructonusterebrans.Thesebeetlesareusuallyconsideredsecondarypestsbecausetheynormallyinfestonlystressed,weakened,damaged,ordownedpines.Theyalsocolonizepinesthathavebeenattackedbysouthernpinebeetlesoranotherbarkbeetlespecies.HostspeciesintheSouthincludeloblolly,shortleaf,Virginia,longleaf,easternwhite,pitch,slash(P.


elliotii),andsand(P.clausa)pines.Bothpurepineandoak-pinestandsmaybeaffected(ConnerandWilkinson1983,SmithandLee1972,USDAForestService1985a).

Attacksbyblackturpentinebeetlesmaycontinueforseveralmonthsbutinfestationisnotalwaysfatal.Multipleattacksaroundtheentirecircumferenceofthetreearerequiredtocausemortality(SmithandLee1972,Staebenandothers2010,USDAForestService1985a).

Thesmallsouthernpineengraverandthesix-spinedengraverarethemostaggressiveandmaykillsmallgroupsoftrees.Lossesmaybeextensiveduringperiodsofdrought(ConnerandWilkinson1983,USDAForestService1985a).

Thesecondarybarkbeetlesplayavitalroleinshapingforeststructureandmayhaveagreaterimpactonregulatingpinestandsthansouthernpinebeetles(Paineandothers1981,Thatcher1960a).Theyattackweakenedorseverelystressedtreesandthosereachingsenescence.Largeinfestationsdeveloponlyoccasionally,usuallyafterwidespreadenvironmentalstress,suchasthatcausedbydrought,stormdamage,orwildfire.Theiractionservestothinthepineforests,reducingcompetition,leavingthestrongertrees,anddecreasingtheriskofsouthernpinebeetle(SPB)outbreaks.

Theimpactofthesebeetlesdependslargelyonmanagementactivities(Coulsonandothers1986).Engraversalsobreedindownedmaterial,soitisdifficulttosubstantiallyreducepopulations,butpreventionmethods(suchasloweringplantingdensities,thinningstands,andcuttingandremovinggroupsofinfestedtrees)canreducedamage.

Inunmanagedstands,theyattacksingletreesorsmallgroupsofpinesandreducepinebasalarea.Theyprovideopeningsforpinereproductionorforestablishedhardwoodstogrow.Theeffectsareoftennotnoticeableexceptduringperiodsofextendeddrought,afterstormdamage,orattheendofSPBepidemics.

Increasedtemperatureanddecreasedprecipitationwouldstresspinesandcouldthereforeincreasetheimpactsofthesebarkbeetles,butitisunlikelythattheywillbecomeprimarypeststhatkilllargeareasoftrees.Thesefourbarkbeetlespeciesmaymovenorthwardaswintersbecomewarmer.

Pine reproduction weevils—Palesweevil(Hylobiuspales)andpitch-eatingweevil(Pachylobiuspicivorus)aretwoofthemostdamaginginsectpestsofpineseedlingsintheSoutheasternUnitedStates.Insouthernforests,theyarefoundwhereverpineoccurs.Adultweevilsofbothspeciesareattractedtonewlyharvestedsites,wheretheybreedinloggingslash,stumps,andoldrootsystems;theycauseeconomiclossesbyfeedingonthebarkandoftenkillingplantedseedlings.Ifseedlingsareplantedonoradjacentto

siteswithfreshstumpsordamagedtrees,itiscommontohave30to60percentweevil-causedmortalityamongfirst-yearseedlings,withinstancesof90percentormoremortalityrecorded(Thatcher1960b).Athirdspecies,theeasternpineweevil(Pissodesnemorensis),isgenerallylesscommonbutisknowntokillterminalandlateralbranchesandgirdlethestemsofsmalltrees(Doggettandothers1977,Nordandothers1984).Thereproductionweevilsarealmostneveraprobleminforestmanagementunlessseedlingshavebeenplantedonoradjacenttositeswithfreshstumpsordamagedtrees.Forestersusuallyavoidthisproblemoncutoversitesbydelayingplantingorbyplantingtreatedseedlings.

Palesandpitch-eatingweevilspreferloblolly,shortleaf,pitch,andeasternwhitepines.Theyalmostneverattacklongleafandslashpines,butonrareoccasionshavebeenobservedfeedingonhardwoods.Althoughtheeasternpineweevilpreferscedar,italsoattacksmostsouthernyellowpines,suchasloblolly,slash,andshortleaf.Palesandeasternpineweevilsmayserveasvectorsforvariouspathogenicfungi.

Thefutureoutlookfortheactivityanddamagelevelsofreproductionweevilsissimilartotherecentpast.AwarmerclimatemayallowtheseinsectstoextendtheirrangesnorthintoCanada.Warmersouthernwintermonthsmayallowthemtoincreaseand/orprolongactivityandtoproducemoregenerationsperyear.Decreasedprecipitationmayreducetheiractivity.Theimpactsofthesepestsaremoredependentonstandmanagement(andwhetherseedlingsweretreatedwithinsecticides)thanonclimaticconditions.Ifpinesareplantedandthenleftunmanagedoverthenext50years,wecanexpectincreaseddamagefrompinereproductionweevils.

Sirex woodwasp—Sirexwoodwasp,Sirexnoctilio,isnativetoEurope,AsiaandnorthernAfricaandhasbeenintroducedtoNorthAmerica,SouthAmerica,NewZealand,Australia,andSouthAfrica.InAustralia,SouthAfrica,andSouthAmerica,itisconsideredanimportantpest,causingsignificantmortality(Oliveiraandothers1998)instandsplantedwithNorthAmericanpines,especiallyMontereypine(P.radiata)andloblollypine.HaugenandHoebeke(2005)reportthatotherknownsusceptiblepinesincludeslash,shortleaf,ponderosa(P.ponderosa),lodgepole(P.contorta),andjack(P.banksiana).

Femalescanproduceupto450eggsanddepositthem(mostlysingly)belowthesurfaceofthebarkclosetothecambium.Thefemalealsodepositsmucusandabasidiomycetesymbioticfungus,Amylostereumareolatum,whichgrowsrapidlyandexcreteswood-digestingenzymes.Whenthelarvaehatchtheyboreintothewood,butfeedonwoodalreadycolonizedbythefungus.Thefungusandmucusacttogethertokillthetreeandcreateanenvironmentsuitableforthedevelopmentofthelarvae.


SirexwoodwasphasnotcausedwidespreadmortalityintheNorthAmericanareaswhereitisestablished,norhaveanypopulationsbeenreportedintheSouth.Howeverwithinthenext50years,itisverylikelythatnaturalorhuman-aidedspreadwillintroducethispesttosouthernforests.ManyoftheSouth’smostimportantpinespeciesaresusceptibletoSirexandmanytreeswillsuccumbifattacksareasaggressiveastheyareinSouthAmericaandAustralia.Althoughthisscenariocouldresultincatastrophicecologicalandeconomiclosses,thecomplexityofsouthernforests(mixedstands,highbiodiversity,manypossiblecompetitors,predatorsandparasitoids)contrastswiththemonoculturepineplantationsinothercountrieswherethepesthasbeenmostdamaging.Manystudiesareunderwaytoassessthepotentiallevelofdangertosouthernforests.AnationalriskmapforSirexhasbeendeveloped(seehttp://www.fs.fed.us/foresthealth/technology/invasives_sirexnoctilio_riskmaps.shtml)andriskmapsspecifictotheSouthareindevelopment.

IftheSirexwoodwaspbecomesestablishedintheSouthandactsasaprimary“treekiller,”effectivepreventionandsuppressiontechniquesareavailable,includingthecurrentpracticeofthinningstandstoincreasegrowthandvigorandreducesusceptibilitytobarkbeetles.Inothercountries,Sirexwoodwasphasbeensuccessfullymanagedusingbiologicalcontrolagents.Thekeyagentisaparasiticnematode,Deladenussiricidicola,whichinfestsSirexwoodwasplarvae,andultimatelysterilizestheadultfemales.Infestedadultfemaleslayinfertileeggsthatarefilledwithnematodes,whichfurtherspreadsthenematodepopulation.Thenematodescaneffectivelyregulatethewoodwasppopulationbelowdamaginglevels.AsSirexwoodwaspestablishesinnewareas,thisnematodecanbeeasilymass-rearedinthelaboratoryandintroducedbyinoculatingitintoinfestedtrees.BiologicalcontrolemployingthesenematodesisbeingevaluatedforuseinU.S.forests.Ifeffective,itshouldprovideagoodcontroloptionforsouthernlandownersandlandmanagers.

Theeffectsofchangesintemperature,carbondioxide,andprecipitationonSirexwoodwaspactivityandaggressivenessareunknown.IfpineacreageincreasesthroughouttheSouthorincertainareasoftheSouth,susceptibilityoftheseareastoattackwillincrease.

Southern pine beetle—Southernpinebeetle(SPB),Dendroctonusfrontalis,isthemostdestructiveinsectpestofpineforestsintheSouth(ThatcherandConner1985).Populationsbuildrapidlyduringperiodicoutbreaksandkilllargenumbersoftrees.Forexample,duringtheoutbreakof1999to2002,SPBkilledmorethanamillionacresofpinesvaluedatgreaterthan$1.5billion.However,duringperiodsoflowactivity,SPBpopulationsmaybesolowthat

itisdifficulttolocateasingleinfestedtree(ThatcherandBarry1982,Thatcherandothers1980)orcapturebeetlesinpheromonetraps(BillingsandUpton2010).

TheSPB,whichattacksallspeciesofpines,prefersloblolly(Pinustaeda),shortleaf(P.echinata),Virginia(P.virginiana),slash(P.elliottii)pond(P.serotina),andpitch(P.rigida)pinesbutseldomattackslongleafpine(P.palustris).SPBhasbeenobservedtosuccessfullyinfesteasternwhite(P.strobus)andTableMountain(P.pungens)pines.Maturetreesinpure,densestandshavelongbeenconsideredmostsusceptibletoSPBattack,butinrecentyearsunthinnedpineplantationshaveincreasinglysupportedSPBinfestations(CameronandBillings1988).Attacksarerarefortreesyoungerthan5yearsorsmallerthan2inchesindiameteratbreastheight(d.b.h.).

Duringoutbreaks,SPBactivitypeaksinearlysummerinStatesontheGulfofMexicoandinlatesummerandearlyautumnfarthernorth.

Inthelastfivedecades,largeacreagesofpineplantationshavebeenestablishedintheSouth.Even-aged,single-speciesplantationsbecomeincreasinglysusceptibletoSPBinfestationsastheyage.MillionsofacresofpineacrosstheSouthareathighhazardforSPBattackasshownbyregionalandStatemaps(Nowak[N.d.]).SPBhazardmapsandinformationabouttheirdevelopmentcanbeviewedat:http://www.fs.fed.us/foresthealth/technology/nidrm_spb.shtml.

SPBimpactsoverthenext50yearsareexpectedtobesignificant,especiallyifthepineacreageincreasesintheSouth,high-susceptibilityspeciesareplantedindenseplantations,andtheplantationsareleftunthinned.Awarmer,drierclimateislikelytoincreaseSPBactivityandimpacts.WarmertemperatureswilllikelyallowanincreaseinthenumberofSPBgenerationsperyearaswellastheportionoftheyearthatthebeetlesareactive.ThenorthernedgesofthesouthernregionandpinestandsthatarefarthernorththanthehistoricalSPBrange(suchasintheLakeStates,NewEngland,andCanada)arealmostcertaintoexperienceSPBactivityandimpactsthatareunprecedentedoratleastsignificantlygreaterthaninthepast.

ThereissomeuncertaintyanddebateaboutthepotentialeffectsofawarmerclimateonSPB(Tranandothers2007),andgeneralpredictionsaredifficulttomake.Anincreaseintemperature(particularlywarmerwinters)wouldallowmoregenerationsperyear.Gan(2004)andRiveraRojasandothers(2010)predictoutbreakstobecomemorefrequentasclimatechanges,althoughlackoflandscape-scaledataonhostabundanceanddistributionmayhaveledGantooverestimatefutureSPBactivity.Veryhighsummertemperaturesmayincreasebroodmortality,reducespotgrowthrates,andhinderpredation.Warmerwintertemperaturesmaydisrupt


synchronizationofthelifecyclesrequiredforconcentratedspringemergencethatfavorsinitiationoflarge,newinfestations(BillingsandKibbe1978).

Theimpactofoutbreaksinthe1980swasmagnifiedbyanabundanceofcontiguousmaturestandsofsawtimber,manyofwhichhavebeenreplacedwithyoungplantations,atleastonnon-Federallands.Ifincreasedforestfragmentation,ayoungerageclassdistribution,andmorethinningofplantationsoccurinthenext50years,SPBimpactscouldbelowerinthefuture,despiteincreasesintemperatures.AndalthoughitisgenerallyacceptedthatincreasedtemperatureswillincreaseSPBactivityanddamage,otherfactors(forexampleforestcomposition,forestmanagement,directsuppression,etc.)maybemoremeaningfulindeterminingfutureSPBactivityanddamage(Friedenbergandothers2008).

Similartotemperature’seffectonSPB,thepotentialofmoistureregimetoincreaseordecreaseSPBproblemsisopentoconjectureandnotfullyunderstood.SomeexpertsbelievethatdroughtisamajorenhancerofSPBoutbreaks,whereasotherspointtotoomuchmoistureasaprimaryfacilitatingfactor.Ifthefrequencyofprecipitationextremes(yearsofextremewetnessordyness)increasesthroughouttheSouthoverthenext50years,itisprobablethatpineswillbecomestressedandincreasedSPBactivityanddamagewillresult.

Inadditiontotheeffectsthatforestcomposition,temperature,andmoisturewillhaveontheSPBoutlook,forestmanagementwillplayadefiningrole.Plantingtheproperspeciesforagivensite,lowerplantingdensities,andthinningofpinestandscanincreasestandvigorandresiliencyandpossiblyreduceSPBdamage.Whenoutbreaksdooccur,damagecanbeminimizedbyearlydetectionandmonitoringofspots,followedbypromptdirectsuppressionofactivespots(Billings1980).

Texas leafcutting ant—TheTexasleafcuttingant,Attatexana,targetsfirst-andsecond-yearpineplantationsineasternTexasandwestcentralLouisiana.Inlocalareaswheretheantsareabundant,itisnearlyimpossibletoestablishpineplantationsunlesstheantcoloniesareeliminated.TheannuallossofpineseedlingstoTexasleafcuttingantsisnearly12,000acres(Cherret1986,TexasForestService1982).

Awarmerclimatemayleadtoanincreaseand/orcontinuationofleafcuttingantactivityduringwintermonths.Decreasedprecipitationwouldlikelyhavetheoppositeeffect.Becausethisanthasastrongpreferenceforwell-drained,deepsandysoils(Moser1984,Vilela1986),climate-inducedspreadbeyonditscurrentdistributionisunlikely.Althoughleafcuttingantsarelimitedbyaveragelowtemperatures(warmertemperatureswouldlessenthislimitingfactor),their

spreadintonew,northernareasisgoingtobelimitedduetothelackofpreferredsoilsfortheant.ThereisapossibilitythatawarmerclimatewouldallownorthwardmovementintoareasofOklahomaandArkansasthathavedeep,sandysoils.Anewfipronilcontrolproduct,PTM™wasregisteredin2009,andaninsecticidalbaitisonthehorizon.RegularandconsistentapplicationoftheseproductshasthepotentialtoreducetheimpactsofTexasleafcuttingantsfromhistoricallevels.

insect Pests of hardwoods

Asian longhorned beetle—Asianlonghornedbeetle,Anoplophoraglabripennis,wasdiscoveredattackinghardwoodtreesintheUnitedStatesinthemid-1990s.Tunnelingbybeetlelarvaegirdlestreestemsandbranches.Repeatedattacksleadtodiebackofthetreecrownand,eventually,deathofthetree.ThebeetleprobablytravelledtotheUnitedStatesinsidesolidwoodpackingmaterialfromChina.ThispestbeetlehasbeeninterceptedatportsandfoundinwarehousesthroughouttheUnitedStatesandiscurrentlyinfestingtreesinNewYorkCity,NewJersey,Worcester(MA),andToronto(Ontario,Canada).ItwassuccessfullyeradicatedfromtheChicagoareafollowingalengthyandaggressivecampaignofdetectionandremovalofinfestedtrees(AntipinandDilley2004).

ThisbeetleisaseriouspestinChina,whereitkillshardwoodtreesinroadsideplantings,shelterbelts,andplantations.IntheUnitedStatesthebeetleprefersmaplespecies,includingboxelder(A.negundo),Norway(A.platanoides),red(A.rubrum),silver(A.saccharinum),andsugar(A.saccharum)maples.Otherpreferredhostsarebirches(Betulaspp.),Ohiobuckeye(Aesculusglabra),elms(Ulmusspp.),horsechestnut(Aesculushippocastanaeum),andwillows(Salixspp.).Occasional-to-rarehostsincludeashes,Europeanmountainash(Sorbussp.),Londonplanetree(Platanussp.),mimosa(Albiziajulebrissin),andpoplars(Populusspp.).AcompletelistofhosttreesintheUnitedStateshasnotbeencompiled.

Asianlonghornedbeetlesproduceonegenerationperyear.AdultbeetlesareusuallypresentfromJulytoOctober,butcanbefoundlaterinthefalliftemperaturesarewarm.Adultsusuallystayonthetreesfromwhichtheyemergedordisperseshortdistancestoanewhosttofeedandreproduce.Eachfemaleusuallyproduces35to90eggs(ormore)duringherlifetime.Eggshatchin10to15days.Thelarvaefeedunderthebarkinthelivingtissueoftheirhostandthenboredeepintothewoodtopupate.Adultsemergebyboringatunnelandcreatingalargeroundexitholeinthetree(USDAForestServiceandAnimalandPlantHealthInspectionService2008).

Currently,theonlyeffectivemeanstoeliminateAsianlonghornedbeetleistoremoveinfestedtreesanddestroy


thembychippingorburning.Topreventfurtherspreadoftheinsect,quarantinesareestablishedtopreventtransportationofinfestedtreesandbranchesfromthearea.Earlydetectionofinfestationsandrapidtreatmentresponsearecrucial.Systemicinsecticidescanprovideprotectionforindividualtreesorsmallnumbersoftrees,butindividualtreetreatmentisnotfeasibleinforestedsettings.

ThefutureimpactofAsianlonghornedbeetlesonsouthernforestsisunknownforseveralreasons.First,thepestmayormaynotspreadintotheSouthoverthenext50years.Significanteradicationandcontainmenteffortsarebeingpursuedinareaswheretreesareunderattack.Althoughthebeetledispersesslowly—itdoesnotflygreatdistancesandtendstoremaininthesameareauntilhostsareexhausted—itmaybespreadgreatdistancesinfirewoodorbymovementofotherinfestedmaterial.

Awidevarietyofsouthernhardwoodtrees(especiallymaples)isatrisk.Itisunlikely,however,thatvastareasofhardwoodswouldbekilledwithinthenext50yearsbecausethebeetletakesseveralyearstokillhosttreesanditisaslowdisperser.Ifspotinfestationsarediscoveredearlyenough,thebeetlecanbeeradicatedbeforeitbecomeswidelyestablished.Successfuleradicationeffortsrequiremuchtime,funding,personnel,andstrengthofwill.

EffectsofsouthernclimateonAsianlonghornedbeetlearecompletelyunknown.ExtremeheatinsomepartsoftheSouthmayinhibitactivityandsuccess.However,thereisalsothepossibilitythatwarmertemperatureswouldleadtoquickercompletionofthebeetle’slifecycle,whichwouldmeanlargerpopulationsandmoredamagetosoutherntrees.

Baldcypress leafroller—Formerlynamedthefruittreeleafroller,thebaldcypressleafroller,Archipsgoyerana,periodicallydefoliatesbaldcypressinLouisianaandMississippi.Kruse(2000)describesthebaldcypressleafroller,andsummarizesitsbiologyanditseffectsonitshost.Thisnativeinsectcausesgrowthreductionanddieback,butonlycausesmortalitywhenmultipleotherstressorsareatwork.

Thebaldcypressleafrollerwasfirstrecordedin1983inLouisiana,whereitfeedsalmostexclusivelyonbaldcypress.Itannuallydefoliatesanaverageof35,000acresintheoak-gum-cypressforesttype.Althoughthisinsectismainlyapestoffloodedbaldcypress,itcanmoveintodrieruplandandurbansettingsduringperiodsofheavyinfestation.

Baldcypresstreesofallsizesdisplaycanopydiebackandsignificantreductionsindiametergrowthresultingfromrepeatedannualdefoliation.Pole-sizedtosmallsawtimber-sizedtreesgrowingonforestedgesorindensestandsaremostseverelyaffected.Inareaswherechronicsaltwater

intrusionisaproblem,treesdieafterasfewastwoconsecutiveyearsofdefoliation.

Temperatureandprecipitationchangesareunlikelytodirectlyaffectbaldcypressleafroller’sactivityandimpacts.However,highersealevelsresultingfromwarmertemperatureswouldfurtherstressbaldcypresstreesbecauseofincreasedsaltwaterintrusion,significantlyincreasingthelikelihoodthatdefoliationwoulddamageandkillhosttrees.HumanalterationstosouthernLouisiana’shydrology,greatersaltwaterintrusion,nutriafeeding,defoliationbybaldcypressleafroller,andotherstressorsareallcombiningtothreatenthebaldcypressresourceinsouthernLouisiana.Althoughunlikelytodisappearinthenext50years,thisresourceisexpectedtocontinuetobecompromised.

Emerald ash borer—Emeraldashborer,Agrilusplanipennis,isadevastating,wood-boringbeetlenativetoAsia.ItwasfirstfoundinfestingtreesinNorthAmericainsoutheasternMichiganandadjacentareasofOntario,Canada,in2002(Various2010).WithinthecoreinfestedareaofMichigan,Indiana,andOhio,morethan50millionashtreesareestimatedtobedead,dying,orinfested(Smithandothers2009).Elsewhere,theemeraldashboreralreadyhaskilledtensofmillionsofashtrees,andcontinuestoposeaseriousthreattotheashresourceofNorthAmerica.

TheemeraldashborerwasfirstfoundintheUnitedStatesin2002,butitwaslikelyintroducedintotheareaaroundDetroitintheearly1990s(Kovacsandothers2009),probablyinsolidwoodpackingmaterialfromAsia.Soonafterdetection,fivecountiesinMichiganwereplacedunderquarantine.However,intheyearsbeforedetection,infestedmaterial—suchasnurserystock,unprocessedashlogs,firewood,andotherashcommodities—wasmostlikelymovedtomanyareasaroundtheUnitedStates.InadvertentmovementbyhumanscontinuesintothepresentinspiteofFederalandStatequarantinesrestrictingtheexportofpotentiallyinfestedmaterialsoncetheborerisdetectedinacounty(U.S.DepartmentofAgricultureAnimalandPlantHealthInspectionService2003,2006).Surveysmadein2003foundinfestationsin12countiesinMichiganand3countiesinnorthernOhio.Byearly2011infestationswerelocatedinanadditional13States:Indiana,Illinois,Iowa,Maryland,Pennsylvania,Missouri,Virginia,WestVirginia,Wisconsin,Kentucky,Minnesota,andNewYork(fig.16.2).InCanada,infestationsnowoccurinseveralareasofOntarioandQuebec(USDAAnimalandPlantHealthInspectionService2011).

Sinceitsintroduction,theemeraldashborerhashadasignificantnegativeimpactontheecologyandeconomyofinfestedareas,withall16speciesofNorthAmericanashappearingtobesusceptible.AshtreesareanimportantpartoftheruralandurbanforestsoftheUnitedStates,valuedatmorethan$282billion(USDAAnimalandPlantHealth


detectinfestationsearlyenoughtoeffectivelycontrolthemandpreventtheirspread.

Thereareanumberofeffectivechemicalcontroloptionsavailabletoprotectindividualtreesfrominfestation(Hermsandothers2009).Unfortunately,availabletime,funding,equipment,andexpertiselimitthenumberoftreesthatcanbeprotectedtourban/suburbansettingsandaverysmallnumberofhighvaluetreesinforestedsettings.Withtheemeraldashborerdestroyingeveryashinitspath,onepracticaloptionmaybetodelineateandprotectsmallpocketsofexceptionalashresourceas“ashconservationareas.”

Severallarvalandeggparasitoidsarebeinginvestigatedforuseasbiologicalcontrolagents(USDAAnimalandPlantHealthInspectionServiceandothers2010).Althoughresultsarepreliminary,itisreasonabletoexpectthatbiologicalcontrolagentswouldmitigatepopulationsbutwouldnotcontrolorcompletelystopthespreadandimpactsofthisinsectinvader.

Theeffectsofchangesinclimate—suchasincreasesintemperature,precipitation,andcarbondioxide—onemeraldashborerareuncertain.Warmertemperatureswouldlikelyresultinmorerapidlifecyclecompletionresultinginincreasedpopulationgrowthandimpacts.However,theextremeheatofsouthernsummerscouldactuallyinhibitactivityandreducetheamountofashmortality.TherangeofashtreesintheSouthisexpectedtoshrinkastheclimatewarms;betweenclimatestressandtheemeraldashborerinfestations,theSouthislikelytolosemillionsofashtreesinthenext50years.

Forest tent caterpillar—Foresttentcaterpillar,Malacosomadisstria,occursthroughoutmostoftheUnitedStatesandCanada,whereitdefoliatesavarietyofhardwoods(BatzerandMorris1978,Drooz1985,Fitzgerald1995,USDAForestService1985b).IntheSouth,itheavilydefoliateswatertupelo(Nyssaaquatica),sweetgum(Liquidambarstyraciflua),blackgum(N.sylvatica),andvariousoakspecies(Quercusspp.).ThemostpersistentandextremeoutbreaksintheSouthoccuronhosttreesinbottomlands,forestedwetlands,andriparianareas.Whenpopulationsreachepidemiclevels,thecaterpillarsoftenspreadtourbanandsuburbanareaswheretheydefoliateshadetreesandornamentalplants.

OutbreaksoccurinseveralSouthernStates,wheremorethan500,000acrescanbedefoliatedinasingleseason;defoliationdoesnotcausesignificantamountsoftreemortalityandthereforecontrolpracticesarerarelycosteffective.However,significantlossoftreegrowthisoftenanoutcome,andrepeated,heavydefoliationofstandsmaycausesignificantdieback.Ifneeded,controltechniquesareavailableand

haveproveneffectivebutdependontheavailabilityofbothfundingandtechnicalexpertise.

Tentcaterpillarimpactsoccurmainlyinthebottomlandhardwood-cypressforesttypes(mappedasoak-gum-cypressandelm-ash-cottonwood),buttheyoccasionallyoccurinuplandnorthernhardwoodforesttypes(mappedasmaple-beech-birch,oak-hickory,andoak-pine).

Changesintemperatureandprecipitationareunlikelytoincreasedefoliationbyforesttentcaterpillars.Ifclimatechangesignificantlystressestheforesttypesmostvulnerabletotentcaterpillardefoliation,theadditiveeffectofmultiplestressorscouldmeanhastenedorincreasedtreemortality.

Gypsy moth—Gypsymoth,Lymantriadispar,isnativetoEuropeandAsia.In1869,LeopoldTrouvelotintroducedtheEuropeanstrainofthegypsymoth.Sincethen,ithasspreadacrossthelandscapeoftheeasternUnitedStates,defoliatingvastacreagesofforest(USDAAnimalandPlantHealthInspectionService2010b).TheinsectwasfoundinnortheasternVirginiaintheearly1980s.Atitscurrentrateofspread,specialistspredictthatasignificantportionoftheSouthwillbeinfestedinthenext50years.

Theimpactofrepeatedgypsymothdefoliationonthehealthofoakforestsissignificant(CampbellandSloan1977).Repeatedseveredefoliationofoaksweakenstreestosuchanextentthattheymaybeattackedandkilledbysecondarypestorganisms,suchasthetwo-linedchestnutborer(Agrilusbilineatus)andArmillariarootrot(causedbyArmillariamellea).Extendeddroughtintensifiesthedeathrate.

Gypsymothcaterpillarsfeedonawiderangeoftreesandshrubs(Liebholdandothers1995,Zhu1994)butpreferoaks.Speciesareattackedpreferentiallywithoutrespecttoforesttype.Highlyfavoredspeciesincludesweetgum,northernredoak(Quercusrubra),andAmericanbasswood(Tiliaamericana).Speciesoflimitedsuitabilityincludepines,maples(Acerspp.),ash(Fraxinusspp.),Americanbeech(Fagusgrandifolia),andcherry(Prunusserotina).Speciesthatarenotfavoredorareavoidedincludeblackgum,yellow-poplar(Liriodendrontulipifera),blacklocust(Robiniapseudoacacia),baldcypress(Taxodiumdistichum),magnolia(Magnoliagrandiflora),andtupelo(Nyssasylvatica).Asgypsymothmovessouthandwest,itwillencounterlowerconcentrationsofoakandcovehardwoods,andforestsusceptibilitywilldecreaseinmanybutnotallareas.However,withitswidehostrangeitshouldstillpersist.

Themostimportantdiseaseagentsaffectinggypsymothsarethegypsymothnucleopolyhedrosisvirus(LdMNPV)andthegypsymothfungus,Entomophagamaimaiga(AndreadisandWeseloh1990,Hajekandothers1990).


TheSlowtheSpreadProgramdecreasesthegypsymoths’rateofspreadfromapproximately25milesayearto7to10milesperyear(Sharovandothers2002).Iftheprogramcontinues,wecanexpectthegypsymothtomove350to500milesfartherintotheSouthoverthenext50years,comparedtototalinfestationwithin25to30yearswithouttheprogram.

Gypsymothscanalsobeartificiallyspreadbyhumanactivities;continuedvigilancetodetectanderadicatetheresultingsmallinfestationshelptopreventthemoth’srapidspreadintoallareasoftheSouth.Inaddition,methodsexisttosuppressareasofhighpopulationsininfestedareasandtoeradicate“satellite”infestationsinadvanceofthemoth’smovingfront;thesemethodsincludeaerialapplicationsofBt(Bacillusthuringiensis)ordimilin(insecticides),orpheromoneflakes(todisruptmating).

Temperaturechangesaloneareunlikelytohaveadramaticeffectongypsymothmovementorimpacts.Therangeofgypsymothinfestationisexpectedtoexpandregardlessofchangesinclimate,andataratefasterthancanbeattributedtoanypotentialclimatechange-causedhostrangeexpansion.Ifwarmertemperaturescausetheoak-hickoryforesttypetodisplaceborealforestsathigherelevationsintheSouth,gypsymothimpactswilllikelyincreaseintheseareas.

However,onehypothesisisthatgypsymothspreadanddamagewilldecreaseastemperatureswarm,therebyreducingtheextentofsouthwardspread.Gypsymothsneedacoldsnaptosynchronizehatches(avoidsdifferentlifestagesfromoccurringatthesametime)andthusimprovematingefficiency.2Ifthishypothesisiscorrect,asthemothmovesfarthersouthandasthetemperatureswarm,winterswouldnotbecoldenoughorthenecessarycoldsnapwouldcometoolateintheyeartosynchronizethespringhatch.

Adrierclimatewouldlikelyincreasegypsymothimpactsbecauseitwouldstresshosttreesanddiscouragebuild-upofthemoth’sfungalpredator,whichthrivesduringwettersprings.

BecausethegypsymothisstillspreadingintotheSouth,barringunforeseencircumstanceswecansaywithcertaintythatitsimpactswillincreaseoverthenext50years.Howsevereandwidespreadtheimpactswillbe,however,isdependentonmanyfactorsincluding:thecontinuationofactiveprogramstoslowthespread,suppressanderadicategypsymoth;theamountandhealthofhardwoodforeststhemothencountersinthefuture;andpotentialunknowntemperatureandmoistureeffectsonthemoth,itshosts,anditsnaturalenemies.

2JohnGhent,USDAForestService,ForestHealthProtection,200W.T.WeaverBlvd.,Asheville,NC28804,828-257-4328,[email protected]:May11,2010.

Hardwood borers—InsectborersareimportantpestsofhardwoodtreesthroughouttheSouth.Theytunnelinthebark,trunks,terminals,androots,causingavarietyofdefectsinwood,stemdeformity,reductionofseedproduction,andtreedecline.

SomeofthemajordamagingborersintheSouth(Solomon1995)arethecarpenterworm(Prionoxystusrobiniae),redoakborer(Enaphalodesrufulus),whiteoakborer(Goestigrinus),redheadedashborer(Neoclytusacuminatus),poplarborer(Saperdacalcarata),oaktimberworm(Arrhenodesminutus),Columbiantimberbeetle(Corthyluscolumbianus),andambrosiabeetle(Xyleboruscelsus).Borersthatareendemictoanareadonotnormallycausediebackandmortality,butinabnormallylargenumberstheycontributetotreedeclineandstanddegradation.Excessivenumbersofgrowthdefectscausedbyborersaffectbetween25and88percentofallhardwoodlogs(WardandMistretta2002).

Intheearly2000s,prolongeddroughtscompromisedthevigorofoaksinnorthernArkansas,leadingtoamassiveredoakboreroutbreak.Althoughtheywerenottheprimarycauseoftheoakmortalityinthatarea,theborerssoonbecamethemostdestructiveagentinthedeclinecomplex.Morethan340,000acresofoakandmixed-oak-pineforestwereseverelyimpacted,withanestimatedlossof500millionboardfeet(morethan$29million)ofoak.

Temperaturechangebyitselfisunlikelytohavemucheffectonhardwoodborerpopulations.Assecondaryinsectpests,theseborersareexpectedtohaveincreasedimpactaspopulationsofhardwoodageanddecline,especiallyduringperiodsofdroughtstress.HardwoodboreractivityanddamageislikelytoincreasethroughouttheSouthoverthenext50yearsifcurrentpredictionsoffutureclimatechangeproveaccurate.

Soapberry borer—Soapberryborer,Agrilusprionurus,anativeofMexico,wasfirstconfirmedineasternTravisCounty,Texas,in2003.Itinfestsandkillswesternsoapberry(Sapindussaponariavar.drummondii),itsonlyknownhost.Reportsbylandownersandarboristsindicatethattheinsecthadprobablybeeninfestingsoapberrytreesforseveralyearspriortobeingidentified.InfestedtreeswereobservedinTravisandMcLennancountiesasearlyas1998.ByJanuary2009,infestationshadbeenreportedin18Texascounties,includingareasnearFortWorth,Dallas,Waco,CollegeStation,Austin,Houston,andCorpusChristi.ByDecember2010,thenumberofcountieshadincreasedto43(Billings2011).3TodatenoinfestationshavebeenobservedinadjacentStates,althoughinfestationsinRobertsCountyintheTexaspanhandleand

3R.Billings,TexasForestService,ForestHealthunit,200TechnologyWay,Suite1281,CollegeStation,TX77845-3424,979-458-6650,[email protected]:March8,2011.


WichitaCountyontheTexas-OklahomabordersuggestthattheinsectmayalreadybeinOklahoma(fig.16.3).

AssoapberryborerpopulationsexpandrapidlyinTexas,thiswood-boringbeetleiskillingallsoapberrytreeslargerthan2inchesd.b.h.Methodsofpreventionandcontrolarebeinginvestigated.Amongthemostpromisingisinjectionofasystemicinsecticide(emamectinbenzoate,registeredforthecontrolofinsectsonconifersandhardwoods,includingthepreventionofemeraldashborer)intouninfestedsoapberrytreesorthoseinearlystagesofattack.Test-injectiontreesarestillbeingmonitored,butearlyresultslookpromising.

Regardlessofclimatechange,itislikelythatwithin50yearstheinsectwillthreatenwesternsoapberrypopulationsthroughoutthetree’sentirerange,whichextendsfromnorthernMexicotoMissouri,andwesttoArizona.

Diseases of Softwoods

Annosum root disease—Annosumrootdisease(ARD),causedbythefungusHeterobasidionannosum(recentlyproposedtoberenamedH.irregulare(OtrosinaandGarboletto2010),producessignificantlossesofconifersacrosstheSouth.Onsandy,well-drainedsites,thisdiseasecausesgrowthlossandmortality.Itismostoftenassociatedwiththinningofloblolly,longleaf,shortleaf,slash,andwhitepineplantations.Thefunguscommonlyinfectsfreshstumpsandthengrowsthroughrootgrafts(rootsthatcomeintophysicalcontactandthengrowtogether,sharingwaterandnutrients)andinfectsresidualtreesonthesite.SlashandloblollypinesarethemostcommonlyplantedspeciesintheSouthandarebothverysusceptibletoARD(Robbins1984,Stambaugh1989).

AsurveyintheSouthdocumented:44to60percentoccurrenceofthisrootdisease;and2to3percentmortalityinplantedpine.Radialandheightgrowtharesignificantlylessfordiseasedpines(Applegate1971,Froelichandothers1977,Morris1970).

TheprimaryriskfactorsassociatedwithARDaretheamountofhosttypeavailable,thesoiltypeandcondition,andthetiminganddegreeofmanagementactivity.Riskdecreasesasclaycontentinthesurfacelayerofsoilincreases,aconditionthatenablesriskmapping(WardandMistretta2002).IntheSouth,riskofARDishighormoderatelyhighonanestimated163.5millionacres,notallcurrentlyforested(Hoffardandothers1995).

TherangeofARDalreadyextendsthroughoutsouthernforestsandintotheborealforestsoftheNorth,makingspreadunlikely.Indeed,itsrangecoulddecreasewitheffortsbymanylandmanagementagenciestorestorethelesssusceptiblelongleafpinetoitspreviousrange

whileconcurrentlypotentialdrought/temperaturerelateddiebackinthesouthernmostpartoftheloblolly/slashpinerangefurtherdecreaseitsrange.Increasedtemperatures,reducedrainfall,andincreasedhostgrowth(frommorecarbondioxideintheatmosphere)wouldallproducesomeincreasesindiseaseactivityresultingfromincreasedhostsusceptibility,butwouldnotsignificantlyincreasefungusvirulence.Itisimprobablethatclimatewarming/dryingwouldaffectpinesusceptibilityonwell-drained,sandysitesandforestedoldfarmfieldssinceonthesesitespotentiallyaffectedpinesarealreadyhighlysusceptibletothedisease.

Managementfordiseasepreventionusingboraxasastumptreatmentinuninfectedstandsshouldcontinuetobeeffective.Dependingontherateoftemperatureincrease,insolation(thermaltreatmentofthestumpsbythesun)maybeeffectiveinpreventinginfectionviastumpsfurthernorththanthe35thparallel,whichisthecurrentlyacceptednorthernlimitofitseffectiveness.

LossofareabyhostspeciesfavoredbyH.annosumshouldleadtoaslightoveralllossofthenegativeimpactofthisdiseaseoverthenext50years.

Brown spot needle disease—Brownspotneedledisease,causedbythefungusScirrhiaacicola,isconsideredthemostdamagingdiseaseoflongleafpine.Itprimarilyaffectsseedlingsbydelayingtheonsetofheightgrowthandcausinglossofpotentialwoodproductionandmortality(ifinfectionissevere).Brownspotissomewhatadiseaseofopportunity:thegrassesthatcompetewithlongleafseedlingsalsomaintainahumidmicroclimatethatcontributessignificantlybothtoinfectionoftheseedlingandtothegeneralsuccessofthedisease.

ThisdiseaseoccursfromVirginiatoTexas,primarilyontheCoastalPlain.Itismoresevereincertaingeographicareas(WardandMistretta2002).Useofcontrolledfirestoremovecompetinggrassesandeliminatedampnessishighlyeffectiveforcontrollingthediseaseandencouragingearlygrowthofseedlings,providedstepsaretakentoavoidsubsequentcolonizationbycompetingnon-nativessuchascogongrass.

Atpresent,longleafpineoccupiesonlyabout5millionacresofitsformer60millionacrerange.Recentrestorationeffortshaveledtotheproductionofhealthierseedlingsforplantingandplantingsuccesshasimprovedonsiteswherelongleafwasoncethedominantspecies(Cordellandothers1989,Kais1989).Overthenext50years,theemphasisonlongleafpinerestorationshouldhaveagreaterimpactonthisdiseasethanclimatewarming.LongleafpineiswelladaptedtosummertemperaturesintheSouthanditisunclearthatincreasesevenashighas1oCwouldhavesignificantimpactonthesouthernextentofthelongleafpinerange.Highertemperaturesmightslightlyfavorincreaseingrowthand


longersummerheatspellsmighttriggerearlyonsetofheightgrowthfromthegrassstagetothecandlestage,endingthepotentialforbrown-spotdamagesooner.Reductionsinrainfall,dew,andfogshouldfavorthelongleafpineoverthefungalpest.Noshiftinaggressivenessofinfectionorvirulenceofthepathogenisforeseen.

Weanticipateasignificantincreaseintheincidenceofbrownspotdisease.Thisexpectationisbasedmoreonincreasedout-plantingoflongleafpineseedlingsthanonclimateinfluences.Thus,althoughclimatechangeisnotexpectedtosignificantlychangethediseaseprofile(itsvirulenceorhostspectrum),humaninterventiontoincreasethequantityofhosttreescouldresultinincreasedincidence.

Fusiform rust—Fusiformrust,causedbythefungusCronartiumfusiformef.sp.fusiforme,occursprimarilyonslashandloblollypines.Itisconsideredthemostdestructivediseaseofsouthernpines,causingtheproductionofcigar-shapedgallsthataregenerallyfatalifformedonthemainstemofthehost(Andersonandothers1980,Czabator1971).

Extensiveplantingofsusceptibleslashandloblollypinessincethe1930shasresultedinanepidemicoffusiformrust,whichnowextendsthroughoutitsavailablehostrangeintheSouth;infectedtreesbeingfoundthroughoutthesouthernpineregion(WardandMistretta2002).LossesaremostseriousonCoastalPlainsitesfromLouisianatosoutheasternSouthCarolina.Severalvariablesincludingweather,amountofinoculum,abundanceofoaks(thealternatehost),andsusceptibilityoftheindividualpinespeciesgovernincidenceofthedisease.Effectivestrategiesareavailableformanagingfusiformrustimpactinplantationsandforestsincludingavoidanceofover-fertilizingseedlingsinthenursery,silviculturalmanipulationofyoungstandstofavorhealthysaplings,andfavoringthedeploymentofgeneticallyscreenedresistantseedlingsinareasofhistorichighrustincidence.

Increaseindiseaserangeinthisregionundertheinfluenceofawarmer,drierclimatechangescenarioisnotaconcernsincethediseaseisalreadydistributedhost-rangewidewithintheregion.However,increasedtemperatureandcarbondioxideintheatmospherecouldcausethepathogentobecomemorevirulentonitscurrenthostbase.Althoughthereissomedisagreementontheeffectofprojectedwarmer,drierclimateregimesonthegeographicrangesforthepinehosts,itisanticipatedthatanylossesofpineincoastalareaswouldbematchedbygainsinthePiedmontandinthelowerreachesoftheAppalachianMountains.

Althoughresearchonrustfungiisinconclusiveandprimarilybasedoncerealgrainsandotherfieldcrops,resultssuggestthattherewouldbegreaterincidenceoffusiformrustsimplyasafunctionofhealthierfungusandhosttrees(Chakrabortyandothers1998).Wealsoanticipatethat

loblollypineatleastwillbeplantedinareasnorthofitscurrentrange;andthattherust,whichinfectsjuveniletissue,willrapidlyfollowintothesenewlyplantedareas.

Overthenext50yearsgiventhegeneralavailabilityofoakalternatehostsforthefungusandtheonlyslightpredictedmigrationofpinefromcoastalareasupwardintotheAppalachianMountains,weexpectthatthepathogenwillsuccessfullyfullycolonizetheextendedrangeofitshosts.Thepotentialeffectofoutplantingrustresistantseedlingsinconjunctionwithpotentialgeographicrangeandclimateshiftsisuncertainatthepresenttime.Iftheresistanceismaintainedinthefaceofchangingconditions,areductionoftheimpactofthisdiseasewouldbeexpectedtooccur.

Littleleaf disease—LittleleafdiseaseisthemostseriouspestofshortleafpinesintheSouth.Itiscausedbyacomplexoffactorsincludinganonnativefungus(Phytophthoracinnamomi),lowsoilnitrogen,erodedsoils,poorinternalsoildrainage,andaplowpan—acompactedlayerofsoilthathasbecomelessporousthanthesoilaboveorbelow,generallytheresultoftillingorotherfarmingoperations(CampbellandCopeland1954).Often,nativenematodes(microscopicroundworms)andnativespeciesofPythium(alsoafungus)areassociatedwiththedisease.Infectedtreeshavereducedgrowthratesandcommonlydiewithin12yearsofsymptomonset.

P.cinnamomiisdistributedthroughout(andwellbeyond)therangecurrentlyoccupiedbyshortleafandloblollypineintheSouth.Shortleafpineisthemostseriouslydamagedsoftwoodhost,withloblollypineaffectedtoalesserextent;Americanchestnutwasitsprimaryhardwoodhost.LittleleafdiseasehasalsobeenreportedonVirginia,pitch,slash,andlongleafpines.AffectedpinestandsarefoundonthePiedmontfromVirginiatoMississippi.ThediseasehasitsgreatestimpactinAlabama,Georgia,andSouthCarolina(WardandMistretta2002,fig.17.10),withadditionalscatteredpocketsoccurringineasternTennesseeandsoutheasternKentucky.Notethat,althoughthefungus’rangeexceedstherangeofitspinehosts,littleleafdiseaseisfurtherrestrictedinwithinthatlargerrangegenerallybysiteconditions.

Thefungushasamobilesporeandneedswatertospreadfromandinfectedhosttouninfectedpotentialhosts;however,thediseasethrivesunderdryconditionsthatstressthehost.Controlstrategiesareavailablebutmost—suchassanitationthinningandsalvagingdeadmaterials—relyontreatmentafterinfectionwhendamageisimminentoralreadyoccurring.

Becauseofitsspecificsiterequirements,spreadintouninfectedsouthernforestsisnotexpected.Further,rehabilitatingsitesbybreakingupoftheplowpansthat


favorthisdiseaseshouldresultinbetterwaterrelationsandareductionininfections.Anincreaseinatmosphericcarbondioxidewouldresultinincreasedgrowthofthehostandgreaterdiseaseexpressioninaffectedtrees.Lossestothisdiseaseshouldcontinueatthesamerateonaffectedsites.However,itsrangeshouldcontractifincreasedtemperaturescauseitshoststomigratenorth,anditsimpactshoulddecreaseovertimeassitesarerehabilitated.

Loblolly pine decline—Reportsofsparse,yellowingcrowns,andlowannualwoodproductioninthepinesofcentral-to-northernAlabamadatebacktothelate1960s(BrownandMcDowell1968,Brownandothers1969).Sincetheearly1990s,localizedincidentsofdecliningpineshavebeenoccurringthroughoutAlabamaandintosouthwesternGeorgia,withadditionalsymptomsincludingrootmortalityanddiscolorationofmanyofthesurvivingrootlets(Hessandothers2003).Recentliteraturesuggeststhepresenceoffungi—includingLeptographiumserpens,L.terebrantis,andL.lundbergii–intherootsofaffectedtrees(Eckhardtandothers2004b);butwhethertheyareprimarypathogensorsimplytakingadvantageofalreadysignificantlyweakenedtreesisstilluncertain.Abarkbeetle,Hylastessp.,hasbeenfoundintherootsystemsofmanydecliningpines,andissuspectedofvectoringthefungusfrominfectedtouninfectedtrees(Eckhardtandothers2004a).Informationislackingonwhethertheyselectweakenedtreestoattackorareindiscriminateintheirattacks(whichwouldsuggestthathealthytreesmaybeabletoovercomesuccessfulinoculation).

Thesymptomsofthedeclineprimarilyoccurinloblollypinesolderthan40years,firstbecomingapparentintreesinthe40to50yearageclass.Mortalitycanoccurbeginningaslittleastwotothreeyearsafterfirstsymptomexpression.LittleisknownaboutthepotentialrangeandseveritybeyondthatfromfieldsurveysincentralnorthernAlabama(Hessandothers2005)andFortBenning,Georgia(Menardandothers2006).Nevertheless,thereisstrongspeculationthatbothabioticandbioticfactorsareinvolvedinpredisposingaffectedstandstodecline.Thesefactorsincludeclimate,wildfire,andhumandisturbancessuchaspreviousagriculture.Coincidently,manyuplandsitesinnorthernandcentralAlabamawereoriginallyconvertedfromsubsistencefarmingtoloblollypineplantationbecauseofloblolly’sout-plantingsuccessrateanditsrapidgrowth.Onetheoryisthatmanyofthesesitesaresimplyunabletosustainsuchrapidgrowthoverthelong-term.

Despitetheuncertaintiesaboutthecausesandprogressionofthisdiseasecomplex,managementstrategiesareinplacethatcanbeimplementedwiththeexpectationofimprovingresistanceoffuturestandsonaffectedsites.Thesestrategiesstartwithapplyingariskratingmodelthatusesdigitalelevationmapsandmappedshapefilesforthesitesin

questioncombinedwithdataonlandformandroothealthofthetreesinthestand.Ifthemodelpredictshazardtoloblollypine,therecommendedalternativespeciesislongleafpine.Forexistingloblollypinestandsonhighhazardsites,therecommendationistothinthembetweenages20and40(Hessandothers2003).Apreviousrecommendation,toallowahigh-risksitetorevertbacktonativehardwoods(Loomis1976,Miller1979),isstillaviable(butseldomadopted)managementoption.

Treedeclineislikelytoincreaseinawarmeranddrierclimate,regardlessofinputsfromdiseaseandinsectvectors.Thisresponsetochangingclimateisamajorfactorinthenorthwardmovementprojectedforthesouthernpines.Increasingincidenceofdeclineshouldeventuallydiminishasnewadaptedecosystemsformintheregion,butthisisnotexpectedtooccurwithinthenext50years.

Diseases of hardwoods

Beech bark disease—Beechbarkdiseaseiscausedbyacomplexoftwoormoreagentsworkinginconcert.Thebeechscale,Cryptococcusfagisuga,attacksthebarkofAmericanbeech,creatinginfectioncourtswhicharesubsequentlycolonizedbythefungusNectriacoccineavar.faginata.Thisfunguscausescankersthatgrowtogetherandgirdlehosttrees.

WhilethebeechscaleisnowacommonpestoftheAmericanbeech,itisnonnative,havingbeenintroducedthroughtheCanadianProvinceofNovaScotiainthelate1800s.Thereisspeculationthatthefungusisalsoanintroducedspecies.Discussiononthatpointissomewhatpointlesssinceanativefungus,N.galligena,isalsocapableofincitingcankersandkillinghostsafterenteringthroughscale-damagedbark.Thescaleisconsideredthepivotalintroductionthatallowedtheinvasivespreadofthisdiseasecomplex(HoustonandO’Brien1983,SouthernAppalachianManandtheBiosphere1996).

Thisdiseasecomplex,firstidentifiedinsouthernforestsintheearly90s,continuestospreadalongabroadfrontandisexpectedtooccupytherangeofitshost(WardandMistretta2002).Intheearlyphaseofitscycle,morethanhalfoftheAmericanbeechtrees10inchesd.b.h.orlargerarekilled.Openingscreatedbydeathorremovalofthebeechresultindensestandsofroot-sprouts,whichproducestandsdominatedbybeechbutlackinganyofitsnormalassociates.Inthesecondphaseofthecycle,revegetatedbeechstandsareattackedlessseverely,resultingincankeredsurvivorsratherthaninextensivemortality.Treesinfectedinthisphasearerarelygirdled,buttheyaregenerallyseverelydeformed.

SincethisdiseasecomplexaffectsonlyAmericanbeech,thereisadirectrelationshipbetweentheamountofbeech


inastandandtheintensityofthedisease.Houston(1997)reportsthatstandageanddensity,treesize,andspeciescompositionaffectdiseaseseverity,especiallyinforestsaffectedforthefirsttime.

Beechbarkdiseaseisenabledbyaninsectvector,sotheprojectionoffutureconditioniscomplicatedbeyondthatofasimplepathogenorinsectdrivenpestsystem.Vectormediationcorrespondstoavailabilityofsporesandhostsusceptibility,andisexpectedtomaintainsynchronicitysufficienttocauseaslightincreaseininfection.Temperatureintoleranceofthehostshouldreducethehost’sgeographicrangeinthefaceofclimatechange.Increasesincarbondioxideshouldincreasehostgrowthallowingaslightincreaseindiseasevirulence.

Ultimately,however,thereductioninavailablehosttreesshouldresultinanoveralldecreaseofsignificanceofbeechbarkdiseaseinsouthernforestsdespitetheprobabilitythatindividualtreeswillexperienceaslightincreaseindiseaseseverity.

Butternut canker—ButternutisbeingkilledthroughoutitsrangeinNorthAmericabyafungus,Sirococcusclavigignenti-juglandacearum,whichcausesmultiplecankersonthemainstemandbranchesofhosttrees.Butternutcankerhasbeenfoundin55countiesintheSouthextendingnorthfromnorthernAlabamaalongtheAppalachianMountainsintoNorthCarolina,Tennessee,Virginia,andKentucky,withscatteredoccurrencesthroughoutKentuckyandTennessee(WardandMistretta2002).ButternutnumbershavebeendramaticallyreducedandthespeciesisnowlistedasaspeciesofSpecialConcerninKentuckyandasThreatenedinTennessee(USDANaturalResourcesConservationService2011).InbothstatesthespeciesislistedasG4/S3.G4indicatesaplantwhichis“…apparentlysecureglobally,thoughitmaybequiterareinpartsofitsrange…”whileS3indicates“…rareanduncommoninthestate…”(USDANaturalResourcesConservationService2008,2009).

DetailedexaminationofcankersindicatesthatbutternutcankerhasbeenpresentintheUnitedStatessincetheearly1960s.Itsoriginisunknownbutitsrapidspreadthroughoutthebutternutrange,itshighlyaggressivenatureoninfectedtrees,thescarcityofresistanttrees,thelackofgeneticdiversityinthefungus,andtheageoftheoldestcankers(40years)supportthetheorythatitisarecentintroduction.DatafromforestinventoriesshowadramaticdecreaseinthenumberoflivebutternuttreesintheUnitedStates(77percentlossinNorthCarolinaandVirginia).

Becausebutternutmakesuplessthan0.5percentofthetreesintheSouth,theoverallcurrentimpactofitslosstotheforestedecosystemintheSouthisconsideredbysometobe

minor.However,asbutternuttreesdie,theyarereplacedbyotheralreadypresentspecies,contributingtoareductionofbiodiversity.

ClimatechangewouldlikelyraisetemperaturesatthehigherelevationsoftheAppalachiansandtheCumberlandPlateau.Thiscoupledwithdrierconditionswouldsignificantlyreducetherangeofbutternutatitssouthernedge.Althoughthehighertemperaturesandpredictedincreasesinatmosphericcarbondioxidecouldincreasethehosttrees’growth,drierconditionsresultingfromreducedprecipitationwouldactagainstthisincrease.OverallweexpecttoseemorecankeringandmortalityoccurringonfewerbutternuttreesintheSouth.

Chestnut blight—Introductionofthechestnutblightfungus,Cryphonectriaparasitica,fromAsia,probablyinthemiddle-to-late1890s,ledtoapermanentchangeinforestecosystems.TheAmericanchestnut(Castaneadentata)wasessentiallylost,notonlyasavaluabletimberspeciesbutalsoasthemostimportantproducerofhardmastforwildlife.Oaksandotherspeciesfilledthevoidsinforeststandsleftbythedeathofchestnut(Hepting1974,Oakandothers1998).Thefunguscontinuestosurviveoninfectedsproutsfromoldchestnutrootstock,variousoaks,andsomeotherhardwoods(Boyce1961).

Nocontrolwasfoundtostoptherapiddevastationcausedbythisblight,andthereislittlechancethatthepathogenwilldisappearorthattheAmericanchestnutwillnaturallyrecoveritspreeminentpositionineasternforests.Researchersintohypovirulencehavediscoveredadiseasethatweakenstheblightfungus,resultinginlessdamagetotheinfectedtree(Anagnostakis1978).Field-testingisunderwayonageneticallyengineeredvirusthatcausesahypovirulentreactionandhasthepotentialtoefficientlyspreadhypovirulencethroughoutthefungalpopulation.

AttemptstocrossAmericanchestnutswithorientalvarietiesandthenbackcrosstotheAmericanparentappeartoofferaviablemethodofmaintainingresistantchestnutinforests(Schlarbaum1988).SelectivelybreedingchestnutsasdescribedhasproducedchestnuthybridclonesthatareundergoingfieldevaluationbytheAmericanChestnutFoundation.Iftheseedlingsovercomeboththeblightandanotherdisease(causedbyPhytophthoracinnamomi)thatwasdevastatingchestnutsatthetimechestnutblightwasintroduced,aseriouseffortcanbemadetoreintroducechestnutintotheAmericanforests.Itistooearlyyettopredicttheoutcomeofthiseffort.However,evenifthehybridsareresistanttothedisease,largeareasofforestlandcannotberestoredtochestnutinthenext50yearsbecausetheseedlingsthatwouldbeneededforthateffortarenotexpectedtobeavailableinlargeenoughquantities.Further,ifclimatechangeisconsidered,theimpactsonchestnut


deployedintherestorationeffortwouldprobablybesimilartothosepredictedforoakssufferingfromoakdecline.

Dogwood anthracnose—Dogwoodanthracnoseiscausedbyanintroducedfungus,Disculadestructiva.ItwasfirstreportedintheUnitedStatesonfloweringdogwood,Cornusflorida,in1978andonwesternfloweringdogwood,C.nuttallii,in1979.Forthepastthreedecades,floweringdogwoodshavebeendecliningataratethatthreatensimportantculturalaspectsofsouthernsociety.Insomeareas,theyhavebeenallbuteliminatedfromtheforestecosystemabove3,000feet(WardandMistretta2002).

Theeasternfloweringdogwoodisasmalltreevaluedbothasasignofspringforruralcommunitiesandforestvisitors,andasanimportantsourceofsoftmastforover100differentspeciesofwildlifethatfeedonitsberries(Kasper2000).Itistypicallyanunderstorytreefoundgrowingwithotherhardwoodssuchasoakandhickory.Severeinfectionisrestrictedtofullyshadedunderstorytreesathigherelevations(above3,000feet)andtothoseonshadedsiteswithanorthernexposure.Thehazardofsevereinfectionandmortalityisgreatestinshaded,moist,andcoolareas.

TherangeofthisdiseasestretchessouthwardintoSouthCarolinaandAlabamaandwestwardintocentralTennesseeandscatteredwesternKentuckycounties(WardandMistretta2002)withactivityconcentratedintheAppalachianMountains.ThesouthernmostlimitofthedogwoodanthracnoserangerelativetoavailablehosttreessuggeststhatthisdiseaseistemperaturelimitedintheSouth.Whetherthislimitationfunctionsatthetimeofsporepropagationordisseminationandhostinfection,orwhetheritactsdirectlytolimitdiseasesuccessisunclear.

Anyprojectedincreaseintheincidenceorvirulenceofdogwoodanthracnosebasedonincreasedhostandfungalgrowthresultingfromhighercarbondioxidelevelsintheatmosphereshouldbeeclipsedbythetemperatureincreasesandpossiblerainfallreductionsprojectedtooccurunderclimatechange.Increasedtemperatureandaridityencroachingathigher-than-currentelevationsintheAppalachianMountainsshoulddiminishtheimportanceofthisdiseaseintheregion,especiallyifithasreachedatemperaturebarrierfarthersouth.Arecolonizationofsomeareascurrentlydenudedofdogwoodbythisdiseasemightbepossible.

Dutch elm disease—TheDutchelmdiseasepathogenisvectoredbyoneoftwobarkbeetlesandcanbecausedbyeitheroftwocloselyrelatedspeciesoffungi:Ophiostomaulmi(formerlycalledCeratocystisulmi);andOphiostomanovo-ulmi,whichismoreaggressiveincausingdisease(Brasier1991).ThesefungiwerefirstintroducedtotheUnitedStatesondiseasedelmlogsfromEuropepriorto

1930.Itisunknownwhenthemoreaggressivespeciesbecameestablished;howeveritwaspossiblypresentasearlyasthe1940sto1950s,andmostlikelycausedmuchofthedevastatingelmmortalitythroughthe1970s.Thelessaggressivespeciesisbecomingincreasinglyrareinnature,andtheaggressivespeciesisthoughttobetheprimarycauseofcurrentmortality.Althoughsomelocalresurgencehasbeenobserved,thereisnoevidencethatthepathogenhasfurtherchanged.Localizedresurgenceismorelikelytheresultofdecreasedmonitoringandsanitationvigilance,abuildupinpopulationsoftheinsectvectors,orhighdensitiesofsusceptiblehosttreesinthewild(Frenchandothers1980,Haugen2007,Hubbes1999).

NativespeciesofNorthAmericanelmsvaryintheirsusceptibilitytoDutchelmdisease.Americanelm(Ulmusamericana)isgenerallyhighlysusceptibleTothediseasewhilewingedelm(U.alata),Septemberelm(U.serotina),slipperyelm(U.rubra),rockelm(U.thomasii),andcedarelm(U.crassifolia)rangefromsusceptibletosomewhatresistant.Nonativeelmsareimmune,butsomeindividualsorcultivarshaveagreaterresistanceorahighertolerancetoinfection(andthereforemayrecoveroratleastsurvive).ManyEuropeanandAsiaticelmsarelesssusceptiblethanAmericanelm(Haugen2007).

Inadditiontogeneticfactorspresentinsomecultivarsandspecies,physicalfactorsaffecttreesusceptibility.Thesefactorsincludeseasonoftheyear,climaticconditions(suchasdrought),andvitalityofthetree.Waterconductingelementsaremostsusceptibletoinfectionbecausetheyareproducedinthespring,makingsusceptibilityhighestfromfirstleafingtomidsummerandlowestduringdroughtconditions.Vigorouslygrowingtreesaregenerallymoresusceptiblethanslowergrowingtrees(D’Arcy2005).

Rootsofthesameorcloselyrelatedtreespeciesgrowingincloseproximityoftencrosseachotherinthesoilandeventuallyfuse(becomegrafted).Thefunguscanmovefrominfectedtreestoadjacenttreesthroughthesegraftedroots.Infectionsthatoccurthroughrootgraftscanspreadveryrapidlythroughoutthetree,becausethefungusiscarriedupwardinthesap.Rootgraftspreadisasignificantcauseoftreedeathinurbanareaswhereelmsarecloselyspaced(Frenchandothers1980,Haugen2007).

Currentmanagementoptionsinurban,suburban,andotherhighvaluesettingsincludesanitizingtoreduceinsectvectors,applyinginsecticidestokillinsectvectors,disruptingrootgrafts;injectingtreeswithfungicide,eradicatingthefungusfromnewlyinfectedtrees(pruning),andplantingresistantortoleranttrees(Frenchandothers1980,HaugenandStennes1999,Newhouseandothers2007,Schefferandothers2008).


Althoughthemosteffectiveactionispromptremovalofstressed,dead,anddyingelms,thisintensityoftreatmentisoftennotfeasible(Haugen2007).

Despitethepresenceofseveralelmspecies(Americanelm,wingedelm,andslipperyelm,atleast)verylittleDutchelmdiseasecanbefoundinareasbelownorthernNorthCarolina,Tennessee,andArkansas.Itappearsthateitherthebeetlesorthefungiinvolvedintransmitting/causingthediseasearetemperaturelimited.Barringsignificantchangesinitspathogen/vectorcombination,increasingtemperatureandmigrationofthehostslightlytothenorthisexpectedtodiminishthedisease’soverallimpactintheSouth.

Laurel wilt—Laurelwiltisaninsect-vectoreddiseasethatiscurrentlydecimatingtheredbay(Perseaborbonia)populationofthesouthernCoastalPlain.ThisdiseasewasfirstidentifiednearPortWentworth,Georgia,in2003andhassubsequentlyspreadnorth,south,andinland(west)fromthatlocation(fig.16.4).Itiscausedbyanintroducedandonlyrecentlyclassifiedfungus,Raffaelealauricola,(Harringtonandothers2008)thatisvectoredfromhosttohostbyanambrosiabeetle(Xyleborusglabratus,alsoanintroducedspecies).Thebeetlecarriesthefungusinpoucheslocatednearitsmandibles.Whenthebeetleboresintothesapwoodthefungusinoculatesthexylem.Onceinoculated,thehostrapidlydevelopsavascularwilt;itsleavesdiegenerallydownwardfromthetop,andthewoodbeneaththebarkbecomesdiscoloredfromstreaking(Fraedrichandothers2008).Infectedhostsdisplayrapiddieback(wiltedleavesanddiscoloredsapwood)andmayormaynotexhibitextrusionoffrass(thefinepowderysawdustandexcrementthatinsectspassaswasteafterdigestingplantmaterial)fromtheinsect’sentryholes.

Severaladditionalhostshavebeenidentifiedforthisvectoreddiseaseincludingswampbay(Perseapalustris),sassafras(Sassafrasalbidum),avocado(Perseaamericana),camphor(Cinnamomumcamphorate),pondberry(Linderamelissifolia),andpondspice(Litseaaestivalis).Redbay,however,isthefavoredhostfortheambrosiabeetleandtothepresenttheseverestdamagehasbeenlimitedtoredbay(Hanulaandothers2008).

Atthepresenttimethereisnoeffectivecontrolknownforthisdiseaseforforestandwoodlanduse.Whilepreliminaryresultsusingpropiconazole(afungicide)showpromiseforpreventingthediseaseintreatedtrees,thenecessityofretreatingthemandthecostoftreatmentsuggeststhatinthefutureusemaybelimitedtotheprotectiononlyofhighvaluetrees(Mayfield2008).Researchintochemicaltreatment,centeredoncontrolofthevector,isongoingbuthasyettoidentifyachemicaleffectiveforthispurpose.Managementrecommendationsemphasizeearlysanitation(removal)ofkilledmaterialbutwiththestrongconcurrent

recommendationthatthedeadmaterialsnotbemovedoffsite,orifmovedoffsitethennotoutoftheknowninfested/infectedarea.Further,itisrecommendedthatwheneverpossiblematerialthathasbeencutdownshouldbechippedorburiedratherthanleftintact(Mayfield2008).

Basedonthecurrentrateofspread(estimatedtobeabout20milesperyear),theknowndistributionofredbay,andregionalclimateprojections,KochandSmith(2008b)haveextrapolatedprobablespreadofthisdiseasethrough2040(fig.16.5).Accordingtotheirprojection,thediseasecomplexwillhavereacheditsnorthernextent(hostbased)by2020,andwillreachthewesternextentofitshostrangeineasternTexasby2040.Thebasisoftheirprojectionsisthecombinationofredbay’snaturalrangeandclimaticbarriersthataffectthevectorandfungus,whichwilllikelystallfurtherprogressofthediseaseintheSouth.Theircaveatisthatprojectionsarelimitedtotheredbayhost.

Unansweredatthispointintimeiswhetherthisfungus/vectorcomplexcouldbecomeestablishedinotherpartsofthecountryonotherlauraceoushosts(suchastheCalifornialaurel)shouldfungus-carryingbeetlesbeintroducedintopotentialnewhostranges.Further,potentialforaffectingthespreadofandpossiblycontrollingsomeofthelossthroughimplementationoftheRecoveryPlanforLaurelWiltonRedbayandOtherForestSpecies(Mayfieldandothers2009)isasyetanunknownfactorinthemanagementofthisdisease.

Unfortunately,in2009,laurelwiltwasdetectedintheSandHillCraneNationalWildlifeReserveinsouthernMississippi—alocationthatwasnotpredictedbyKochandSmith(2008b)forinfectionuntilabout2017—apparentlythroughhumanintroduction.Regardlesswhetherthisisanewintroductionormovementfromtheeastcoastinfectedarea,ithasreducedby8yearsthedisease’sexpectedarrivalinTexas.

Ofconcerniswhetherthediseasemightexpanditshostrangeundertheinfluenceofclimatechangeorthroughamodificationofthefungus/vectorcomplexthatwouldallowanewinsectvectortobecomeinvolved.Ifeitheroccurs,thereisstrongpotentialforcurrentlyunpredictedinvolvementofnewhostsandunpredictedspread;newnessofthiscomplexintheSouthleadstoextremeuncertaintywhenattemptingtoprojectfuturebehavior.

Giventherapidandseveredamagedonetotheinfectedhostscoupledwithpredictedshiftsincoastalvegetationresultingfromprojectedtemperatureincreasesandpossiblydecreasingprecipitation,thepotentialofthisdiseasetospreadbeyonditsprojectedrangeishighlyuncertain.

Oak decline—Becauseofthehistoryofwoodsgrazing,widespreadwildfire,andexploitiveloggingforwood


oakdeclineepisodescontinuetooccurintheregion(primarilyinArkansasandVirginia)wherepredisposingconditions,incitingevents,andcontributingfactorsarecoincident(Gysel1957,Oakandothers1988,Starkeyandothers2000).

Withincreasedtemperatureand(possibly)lessrainfallbeingpredicted,oakdeclineisexpectedtoincrease,possiblysignificantly.Declineresultingfromthestressesimposedshouldbecontributorytoeliminationofoakinsomedrierareas,anditisuncertainwhatcommunityofplantswouldreplacetheoakonthesesites.

Oak wilt—OakwiltisavascularwiltdiseaseofoaksthatisfoundonlyinNorthAmerica.Thecausalfungus,Ceratocystisfagacearum,wasfirstidentifiedinWisconsinin1942.ScientistsbelievedthediseasetobenativetoNorthAmericaandtohavebeenpresentlongbeforeitsdiscovery(MacDonald1995,TainterandBaker1996).Recently,strongspeculationhasbeenvoicedthatthefungusisactuallyanonnativeintroduction,possiblyfromSouthAmericawhereitoccurswithoutcausingdisease(Juzwickandothers2008).Oakwiltoccursin21CentralandEasternStates(RexrodeandBrown1983);9ofthe13SouthernStatesareknowntoharborthedisease,butseveremortalityislimitedtoarecentoutbreakincentralTexas(WardandMistretta2002).

Oakwiltcausesaffectedtreestowiltandusuallytodie.Allspeciesofoakaresusceptible,butspeciesintheredoakgroup—northernred(Quercusrubra),scarlet(Q.coccinea),andblack(Q.velutina)oak—aremostreadilykilled.Oaksinthewhiteoakgroup—white(Q.alba),post(Q.stellata),andchestnut(Q.prinus)oaks—areinfectedbutmortalityoccursmuchlessfrequentlyandmoreslowly.Liveoaks(Q.virginiana)dieatarategenerallyintermediatebetweenredandwhiteoaks.

Sap-feedingbeetlescancarryfungalsporestonearbyhealthytrees,thefunguscancolonizeneighboringuninfectedtreesbygrowingthroughrootgrafts,andhumanmediatedtransmissionisalsopossible(movinginfectedfirewoodwithintactbarkallowsfruitingofthefungusinareascurrentlynotinfected).

Itisunclearwhetherthenorth-to-southprogressofthediseasewashaltedbyatemperaturebarrierthatlimitsmigrationofthefungus.TheexistenceofsuchabarriercouldmeanthattheTexasoutbreakistheresultofarelativelyrecentadaptationofthefungustoahighertemperatureregimeoranadaptationtothehosts(liveoak)attackedinthatarea.RegardlessofwhatcausedtherecentsurgeinoakwiltactivityinTexas,itsrapidspreadraisesthepracticalquestionofwhetherthefunguscannowspreadthroughouttheuninfectedareasfromLouisianatoGeorgiaandFlorida.Weanticipatethatthisquestionmaybeansweredwithinthe

next10to20yearsasthediseaseappearstobespreading(orbeingspreadbyhumans)atafairlyrapidrate.

Increasingsoiltemperaturemightprovideafurtherbarriertospread,ifindeedtemperaturehasbeenabarrier.Predictingthedirecteffectsoftemperatureandatmosphericcarbondioxideonthisdiseasewillrequireanunderstandingofthepathogen-hostmechanismsatplay:whetherdamagetotherootsystemissufficienttocausesymptomsanddeath,orwhetherthefungusmustgrowfromtherootsystem(wheremostofthetransmissionisoccurring)intoandthroughoutthevascularsystemabovegroundtocausethesameeffect.

Littlecanbesaidwithanydegreeofcertaintyaboutpossibleinsecttransmissionofthisdisease.Consistentbutinefficienttransmissionbysap-feedingbeetles(NitidulidsandScolytids)isanacceptedmodeofspread.Shotholeborershavealsobeensuggested,butthese,andotherpossibleinsects,arelessaccepted.Longerperiodsofactivityoftheseinsects,resultingfromthelengtheningofsummers(alreadybeingobserved),couldgreatlyincreasetransmission.However,thisincreasecouldonlyoccuriffruitingmatsofthefungus(which,inTexas,isassociatedwithcoolerandmoisterfall,winterandspringconditions;nottheanticipatedconditions)werepresentduringthetimeinwhichtheinsectsareactive.UnlessincreasedtemperaturetriggersmorematformationthanhasbeenhistoricallyreportedinCentralTexas(unlikely),itisnotexpectedthatadditionalinsectswouldbecomesignificantcarriersofthefungustouninfectedtrees.Possiblelossofsomecoastalforesttosavannashouldhaveonlyaslightimpact:simplyreducingthenumberofhostslessensdiseaseincidence.

Managementofthisdiseasehasproventobeexpensiveandisgenerallyreservedforhighvalue(aestheticallydesirable)trees.Giventheapparentadaptationofthefungustowarmertemperaturesandrelativelydryconditions,andthelimitationsofcontroltacticsavailable,thereisahighprobabilityofsignificantoaklossinpreviouslyunaffectedareasalongtheGulfofMexicoandinGeorgiawithin50years.However,iftheapparentadaptationtowarmeranddrierconditionsprovesinadequateforcontinueddiseasespread,wewouldexpectanoverallslightlesseningoftheimpactofoakwiltintheSouth.

Sudden oak death—FirstreportedinCaliforniain1995,suddenoakdeath(SOD)isnowawell-establishedpestwithafairlylimitedrangeinCaliforniaandOregon.However,despitethisrelativelylimitedcurrentrange,itisbelievedthatifintroducedintotheeasternoakforesttheconsequencescouldbedire.

Literaturerelatingtothisdiseaseisextensive,buthasrecentlybeenreviewed(Kliejunas2010)andmuchofwhat


followshasbeenextractedfromorcrosscheckedwiththatreviewtolimitthenumberofcitationsincludedhere.Thispublication,whichincludesa58pagebibliographyofrelevantliterature,isavailableontheinternetathttp://www.fs.fed.us/psw/publications/documents/psw_gtr234/.

SuddenoakdeathiscausedbyPhytophthoraramorum,afungus,whichcausesseveralnonspecificsymptomsdependingonthehostandhostpartaffected.Symptomsincludestemorbolecankers,twigblight(dieback),andleafblight.Individualplantspeciescandisplaymorethanoneoronlyonesymptomtype(seehttp://rapra.csl.gov.uk/background/hosts.cfmforlinkstoimagesofsymptomsonavarietyofhosts).

Cankersappearinthephloem(tissuesthatcarrysugarsawayfromtheleavesofatree)whichmaybediscoloredabrightred,andspreaduntiltheyreachthexylem(tissuesthatcarrywaterandmineralsupfromtheroot;woodfiber).Cankersaresunken,“bleed”sap,andaregenerallyrestrictedtothelowerportionofthetreetrunk.Theamountofbleedingisvariableevenonasingletreeandmayberelatedtoenvironmentallyavailablewaterandtheageofthecanker.Declinesymptoms(lossofleaves)andcrowndeathfirstappearatthetopofthetreeandspreadrapidlydownthroughthecrownoftenresultingintreedeath(Garbelottoandothers2001).

Thelistofhostscurrentlyreportedforthispestisextensive.Asof2010thelistincludes45provenregulatedhostsplusanother82associatedhostsregulatedinthenurserytrade(USDAAnimalandPlantHealthInspectionService2010a).HostswithstemorbranchcankeringincludeCaliforniatanoak(Lithocarpusdensiflora),coastliveoak(Quercusagrifolia),Californiablackoak(Quercuskelloggii),andShreve’soak(Quercusparvulavar.shrevei).Inaddition,fieldandgreenhouseinoculationexperiments(Rizzoandothers2002)confirmthatthefunguscancauseavarietyofleafandbranchsymptoms,butgenerallynotstemcankering,onrhododendronandazalea(Rhododendronspp.),madrone(Arbutusmenziesii),huckleberry(Vaciniumovatum),manzanita(Arctostaphylossp.),Californiabaylaurel(Umbellulariacalifornica),buckeye(Aesculuscalifornica),bigleafmaple(Acermacrophyllum),toyon(Heteromelesarbutifolia),Californiacoffeeberry(Rhamnuscalifornica),honeysuckle(Lonicerahispidula),andalonglistofotherplants.

Althoughfewofthesespeciesoccurineasternforests,severalofthemcanbefoundinsignificantnumbers.EarlyresultsbyRizzoandothers(2002)showthatnorthernredoakandpinoak(Q.palustirs)aresusceptibletoinfection.InCaliforniagreenhousetests,seedlingsofbotheasternoakspeciesdevelopedlesionsalmosttwiceaslongasthoseformedontheoakseedlingsfromPacificcoastalareasandroughlyequaltothoseformedontanoak(consideredthemostsusceptiblespeciesinCalifornia).Theseresultssuggest

that,allconditionsbeingequal,thesespeciesshouldbehighlysusceptibletosuddenoakdeath.

Kliejunas(2003)ratedtheriskposedbythisdiseaseasveryhigh,butcautionsthatthedegreeofuncertaintyrelatedtofuturediseaseriskisalsohighbasedonlackofknowledgeaboutthehostrange.Notingtheabsenceofcontrolmeasures,hisriskassessmentpredictsrapidspreadbywind,water,andhumantransportofinfectedplants;andsuggeststhepotentialforsevereeconomicandecologiclosses,reductionsinbiodiversity,andindirectimpactsonsensitiveorcriticalhabitatforat-riskplantandanimalcommunities.

Basedonpasthistorywithinvasivespecies,itiseasytoprojectthatitisnotamatterof“if,”but“when,”suddenoakdeathwillgainafootholdineasternoakforests(seealternativehypothesisbelowas“Note”).Ifthediseasereachessouthernforests,therolethatclimatewouldplayisfarfromcertain.Alsouncertain,lackingbasicepidemiologicalresearch,isthepotentialeffectsoneasternspecies;thesecouldrangefrominsignificanttopotentiallycatastrophic(rivalingtheeffectsofchestnutblight).

Suddenoakdeathappearstohavethepotentialtodevastatetheeasternoakpopulation,evenabsentclimatechangeconsiderations(Kliejunas2010,chapter4).Increasedtemperaturesandatmosphericcarbondioxidecouldbeexpectedtoincreasegrowthofboththepathogenanditshost,atleastintheshortterm.Thateffectwouldbesomewhatcounteractedbyreductionsinprecipitationandincreasedozoneinconjunctionwiththewarmertemperatures.Nevertheless,onceacclimatedtotheeasternforest,thediseasewouldprobablyspreadevenfasterthanithasinCalifornia.

Usingthedistributionofknownorlikelyhosts,climateconditionsadequateforthesurvivalandpropagationofthepathogen,andprobablepathwaysofintroductionofthediseaseoutsideofitscurrentrangeKochandSmith(2008a;fig.16.6)projectapotentialrangeforthisdisease.VerysimilarpotentialrangeisindicatedbyDEFRA,Fowlerandothers,andMargaryandothers.KellyandothersandVenetteandCohenproposesomewhatdifferentpotentialrangesbutbothincludesignificantSouthernforestareas(Kliejunas2010,chapter4).

Climate-inducedlossesofnativeoaksattheirsouthernmargins(Iversonandothers1999)wouldreducethepotentialincidenceofdisease,butonlyslightly,andwouldnotslowtheprogressofthediseaseinotherpartsofitspotentialrange.Sturrockandothers(2011)statethat,basedonCLIMEXprojections,changingclimatewilldecreasesubstantiallytheareaintheEasternUnitedStatesfavorableorveryfavorableforP.ramorum.


counties(withsuspecttreesoccurringinsimilarsettingsinanadditional10counties);asyetnowoodlandorforestsurveyshavebeenconducted.AlthoughtheTennesseeinfectionswerethefirstreportedeastoftheGreatPlains,theymayhavebeenoccurringsincethe1990s.Thefullextentofthisinfectionisasyettobedetermined.

Symptomsofthediseaseincludeafoliagewiltinwhichtheleavesprogressrapidlyfromgreenthroughyellowandthentobrown.Wiltingprogressesfromthetopofthecrowndownwardasbranchesdie.IntheWest,thediebackandultimatedeathofinfectedtreestakesaboutthreeyears.Symptomsatfirst(andcertainlywhenobservedatadistance)resemblethosecausedbydrought.Closerinspectionofdeadbranchesrevealsmanybeetleentryholesthroughthebarkandmany(oftensmall)cankersjustunderthebark.Ascankersincreaseinnumberandeachgrowsbiggeruntiltheareasofdeadtissuecoalesceandgirdlethebranch.Inthelaterstagesofdiebackthebeetlesmayattacktheboleofthetreeacceleratingitsdeath(Seyboldandothers2010).

Controlmeasuresforthousandcankersdiseasehavebeenproposedbutnotyetevaluated.BecausethecurrentrangeofthefungalpestisgenerallyhotteranddrierthanTennessee’sclimate,thediseaseishighlyunlikelytoencountertemperaturebarriersthatwouldlimititsspreadintosouthernforests.Andpredictedawarmingclimateislikelytohavelittleeffect;thepathogenandvectororiginatedinahotdryareaoftheSouthwestbutbothhavemovedintothecooler,moisterclimateofcentralTennessee.Findingnobarrierstospread,thousandcankersdiseasecouldoccupytheentirerangeofblackwalnutwithin50years,similartotheprojectedspreadoflaurelwilt.

Additional concerns

Althoughwecanmakerelativelyuncertainpredictionsaboutthefutureofknownpests,predictingcurrentlyendemicorganismsthatmaybecomepestsororganismsfromotherlocationsthatmayinvadetheSouthisvirtuallyimpossible.Lovettandothers(2006)predictthatforestpestswillbetheprimarysourceofchangesineasternforestsbutcautionedagainstspeculationonspecificchangesorspecificpestintroductions.

Animportantconsiderationishumancausedchangeintheforestlandbasedrivenbyincreasingandshiftingpopulationsandeconomicconditions.Asshowninchapter5,alloftheCornerstoneFuturesforecastthattotalforestacreagewilldeclineoverthenext50years,onlyplantedpineisexpectedtoexpand,theoak-hickorytypeisexpectedtoremainrelativelystable,butthethreeotherforesttypesconsideredareexpectedtodecline.Additionally,totalforestbiomassisexpectedtoincreaseatfirstbutthendeclinesomewhat.

Ageneralizedimplicationofthesepotentialshiftsisrelativelystraightforward.Becausepestactivityappearstobebasicallyalinearresponsetoavailability,lessbiomasswouldindicateless(inabsoluteterms)lossofbiomasstopests.However,plantedsoftwoodswouldbeexpectedtoshowanincreaseinabsolutelossproportionaltotheincreaseinplantedacreage.

Thepossibleeffectsoffragmentation,parcelization,andurbanizationonpestimpactsandmanagementaresocomplex(andlargelyunknown)thatitisnotprudentorfeasibletoattempttoidentifyspecificinteractions.Generally,parcelization(greaternumberoflandownersonsmallerunitsofland)maycomplicatepestpreventionand/orsuppressionbymakingitmoredifficulttoattaineffectivemanagementonsignificantacreagesduetothegreaternumberoflandownersinvolved.Ontheotherhand,fragmentationandurbanizationwouldinterruptordecreasetheamountandcontinuityofhostspecies,therebypotentiallydecreasingthespreadandimpactsofpests.

Weexpectcontinuingintroduction(throughinternationalanddomesticcommerceandtourism)ofnonnativeinsectsanddiseaseswhichcouldbecomepestsofforesttrees,despiteimpositionofinspectionsandquarantines.Whichorganismsmightbeintroduced,andthenwhichofthesemightbecomepestspeciesisthesourceofsignificantspeculation,butisrelativelyunpredictable.

DiScuSSioN AND coNcluSioNS

Future considerations for Pest-host Relationships

Plannedadaptation(SpittlehouseandStewart2003)shouldreducevulnerabilityforcommercialtreespeciesatselectedsites.However,manyforestspecieswillhavetoadaptautonomouslyandsocietywillhavetoadjusttotheresult(Winnett1998).Forestpestdistributionchangescausedbyclimatechangearelikelycloselytiedtoshiftsinhostdistribution(Sturrock2007).

Someecosystemsareexpectedtobenew:newcommunitiesoftreeandplantspecieswithdifferentsuitesofinsectsandpathogens.Ifforestsdoremainonaparticularsite,similarfunctionaltypesofinsectsandpathogensarelikelytoremain,althoughtheymaybeincludedifferentspeciesthanatpresent(Beukemaandothers2007).Pathogensexpandingtheirrangesandcontacting‘new’hostsandvectorsmaymeanthatnewpathosystemsprobablywillemerge.Interactionsbetweenpathogensmaychange(Sturrock2007).


Climatechangemayamplifytheimpactandaggressivenessofpathogensoralterthebalancebetweenpathogensandtheirnaturalenemies;itmayalsochangethestatusofweak/opportunisticpathogenssuchthattheyareabletoinfectanddamagestressedtreehosts(Sturrock2007).

Treedeclineislikelytoincreaseinawarmeranddrierclimate,regardlessofinputsfromdiseasesandinsects.Theeffectofwarmeranddrierclimateistostresstreesusedtoacoolerandmoisterregime.Thisstressaloneshouldcauseanincreaseintheincidenceofdecliningtrees,butcompoundedbythepresenceofopportunisticinsectsandpathogens,thereisastrongpossibilitythatthisincreaseindecliningtreescouldbesignificant.Increasingincidenceofdeclineshouldeventuallydiminishasnewadaptedecosystemsformintheregion,butthisisnotexpectedtooccurwithinthenext50years.

Almosteverystudyandreviewofclimatechangeeffectsonforestshasacommoncaveat—thecomplexityoftheecosystemsandpestsystems,aboutwhichrelativelylittleisknown(Sturrock2007).ThedifficultyinpredictingthefutureofplantdiseaseishighlightedbyWoodsandothers(2005),whoreportonanendemicneedleblightfungus(Mycosphaerellapini)thatpreviouslyhadonlyminimalimpactonnativeforesttreesinBritishColumbia.However,recently,inapparentresponsetoalocalincreaseinsummerprecipitation,thisdiseasehasbeencausingextensivemortalityoflodgepolepines.Whileadmittingthatestablishingcausalityoftheincreasedvirulenceofthisendemicpathogenisfraughtwithriskofmisinterpretationoftheevidence,theyindicatethelinktoprecipitation(whiledismissingwarmertemperatures)appearstobefargreaterthan“circumstantial.”Nopriorindicationofthisshifttovirulenceappearsintheliterature—theeventwasunprecedented,unpredicted,andpossiblyunpredictable.Inpartialconfirmation,Sturrock(2007)notesthatwetterspringsinsomeregionsmayresultinincreasedfoliagediseaseswithoutventuringtopredictsubsequentpossiblehost/pestscenarios.

Endemicrootrotfungi(Inonotusschweinitzeii,I.tomentosus,orGanodermaspp.),whichcurrentlycauselimiteddamage,orinsectssuchasengraverbeetlesorspeciesofwoodborerscouldbecomeimportantmanagementconcernsorcouldfadeintoobscurityfromamanagementstandpoint.Thefungithatcauselittleleafdisease,suddenoakdeath(BrasierandScott1994),andotherinfectionsarepredictedtoincreasetheiractivityintemperatezonesintheNorthernandSouthernHemispheresastheymigrateawayfromthetropics.UnderchangingclimaticconditionsthesefungiareexpectedtocausemoredamagetoexistingurbanandforesttreehostsintheSouthandtoexpandthenumberofspeciestheycaninfect.Expectedtobeespeciallyprevalentanddamaging

arethose,likethelittleleafdiseasefungus,thatcangrowintemperatureshigherthan28oC(Broadmeadow2005).

Increaseddroughtstressonhostsmaymeanincreasedmortalityfromrootpathogens.PathogenicArmillariaspp.fungimaybeassistedbytheimpairmentofhosttolerancecausedbyclimatechange-inducedstress:thismayenablelesspathogenicfungitobecomemoresuccessfulonstressedtrees(Sturrock2007).Incidenceofoakandbeechdecline,highlycomplexdisorders,islikelytoincreaseifthepredictedfrequencyandseverityofsummerdroughtstressproveaccurate(Broadmeadow2005).

Achangingclimatewithincreasedtemperatures,increasedevapotranspiration,andextremeweathereventswouldincreasethefrequencyandseverityofstressfactors,whichmayleadtomorefrequentforestdeclines(Sturrock2007).Pathogenevolutioncouldbeacceleratedbymutationresultingfromincreasedsunlightorincreasedreproductionrates(shorterlifecyclesunderhighertemperatures)thatcouldleadtohostresistancebeingovercomemorerapidly(CoakleyandScherm1996).

Basedontheseoccurrencesandtrends,thefollowingbasicpatternshaveemergedonwhichwehavebuiltourprojectionsoffutureimpactsofpests:

•Thecurrentemphasisonlongleafpinerestoration,coupledwithincreasingtemperatureanddecreasingrainfallshouldresultinameasurableshiftinthepopulationdistributionofsouthernyellowpinetypes,bothspatiallyandnumerically.

•BorealforestspeciesareexpectedtohavereducedrangesintheSouthduetothecombinedeffectsofincreasedtemperatureanddecreasedavailablewater.

• Pestsassociatedwithsouthernhostspeciesareexpectedtomigratewiththeirhostswithfewexceptions.TheexceptionsarethosepeststhatalreadyoccurthroughouttheSouthandextendintothenorthernpartoftheUnitedStates.

•Althoughlong-termprojectionssuggestthatcoastalsavannahwillreplaceforestsinmanycoastalandcoastal-plainlocations,theprogressofthischangewithinthenext50yearsisnotexpectedtobesevere.

•Mostrootrottingdiseasesareexpectedtorespondaggressivelytothecombinationofwarmersoiltemperatureandreducedprecipitation.Thiscombinationofheatanddroughtisexpectedtoresultinanincreaseindiebackanddeclineamongmanytreespecies,oftenprovidingfurtherstressthatcouldactasaprecursortosuccessfulinvasion/colonizationbyrootrottingfungi.Newlystressedtreesalsomaybecomethefocusofinsectattack.

•Treessufferinglong-termstressmayprovetobemoreresistanttosecondarypestattackbecauseoflowerphysiologicalactivityandreducedavailabilityofresourcesneededbypestorganisms.


•Treediseaseswhichaffectprimarilystemandbranchtissuearesubjectdirectlytothepotentialeffectsofwarmertemperaturesandadrierenvironment.Atfirst,warmertemperaturesandincreasedcarbondioxideintheatmosphereareexpectedtohaveastimulatoryeffectonbothhostandpathogen.However,theanticipatedloweravailabilityofwatershouldgenerallyfunctionmoreagainstthehostplantthanthefungiinfectingit,favoringanincreaseindisease.Thisassumesthatthetemperatureincreasedoesnotexceedthethermaldeathpointofthefungusoritsspores.

• Foliageattackingfungiaresubjecttosignificantpressurefromlightandthemicroclimateinthehost’sleaves.Althoughsignificantlossofsporeviabilityiscommonontheuppersurfaceofleaves,anychangeintheamountofsunlightwillnormallyalterthesurvivalrate;moresunlightresultsinlowersporesurvivalandlesssuccessfulinfectionandviceversa.Themicroclimateoftheundersideofleavesisalsocriticaltothesuccessoffoliarpathogens.Loweratmosphericmoistureresultingfromlessrainfall,fog,anddew(withasecondaryeffectofreducedsecretionofliquids)isexpectedtoreducetheeffectivenessofcolonizationbyleaf-infectingfungi.

• Longerandwarmersummertimetemperaturesareexpectedtoincreasepathogenandinsectactivity.Insectpopulationsmayshowsimpleincreasesinnumberduetotheavailabilityofadditionalhostmaterialonwhichtobrowse,ormaybeabletoproduceanadditionalgenerationeachyear.

managing Pests under changing conditions

Manyland-managementdecisionsmadetodayarebasedontheassumptionthattheclimatewillremainrelativelystablethroughoutaforest’slife—anassumptionthatmayhaveworkedwellinthepastbutisbeingchallengedbyclimatechange.Evenwithoutaclearviewofthefutureclimateandforest,itispossibletodevelopadaptivestrategiesnow.Adaptationinforestmanagementrequiresaplannedresponsewellinadvanceoftheimpactsofclimatechange(SpittlehouseandStewart2003).Thisisespeciallyimportantwhentherotationperiodsarelong(LemmenandWarren2004).

Changesinclimate,especiallyiftheyleadtogreatervariabilityamongandwithinregions,tendtoaddextrauncertaintytodecisionmaking(Garrettandothers2006).Burtonandothers(2002)appeartocontesttheconclusionofSpittlehouseandStewart(2003)citedabovewiththeirconclusionthatdevelopmentofadaptationmeasuresforsometimeinthefuture,underanuncertainclimate,inanunknownsocioeconomiccontextisboundtobehighlyspeculative.Notso;reconcilingtheapparentcontradictionhereisthenecessitythatbestprofessionaljudgmentratherthanprovensciencebebroughttobearonplanningforanuncertain,butgenerallypredictedfuture.

Adaptivestrategiesincluderesilienceoptionsandresponseoptions.Mitigationoptionsincludeoptionstosequestercarbonandreduceoverallgreenhousegasemissions(Millarandothers2007).Copingstrategiesforonedisturbancetypeareoftenappropriatemanagementresponsestootherdisturbancetypes.Beforedisturbanceoccursforestscanbemanagedtoreducevulnerabilityortoenhancerecovery.Treescanbeplantedthatarelesssusceptibletodisturbance.Speciesthatpromotedisturbancecanberemoved(Daleandothers2001).Millarandothers(2007)proposethefollowinggeneralizedstrategies:

• Improve resistance in hosts: Fromhigh-valueplantationsneartoharvesttohigh-priorityendangeredspecieswithlimitedavailablehabitat,maintainingthestatusquoforashorttimemaybetheonlyorthebestoption.Resistancepracticesseektoimproveforestdefensesagainstdirectandindirecteffectsofrapidenvironmentalchangesbyreducingtheundesirableorextremeeffectsoffires,insects,anddiseases.Becausetheymayrequireintensiveintervention,theseoptionsarebestappliedonlyintheshort-term.

•Promote resilience to change: Resilientforestsarethosethatnotonlyaccommodategradualchangesrelatedtoclimatebutalsotendtoreturntowardapriorconditionafterdisturbance,eithernaturallyorwithmanagementassistance.Promotingresilienceisthemostcommonlysuggestedadaptiveoptiondiscussedinaclimatechangecontext.Thisprocessmayalsobecomeintensiveaschangesinclimateaccumulateovertime.

•Enable forests to respond to change: Theseadaptationoptionsintentionallyaccommodatechangeratherthanresistit.Treatmentsimplementedwouldmimic,assist,orenableongoingnaturaladaptiveprocessessuchasspeciesdispersalandmigration,populationmortalityandcolonization,communitycompositionanddominancewithincommunities,anddisturbanceregimes.Somepotentialpracticesinclude:(1)Increaseredundancyandbuffers,manageforasynchrony,realignsignificantlydisruptedconditions,anduseestablishmentphasetoresetsuccession;(2)Establish“neo-native”forests,experimentwithrefugia,andpromoteconnectedlandscapes;(3)Developindicatorsasaprerequisiteforanykindofdecisionmakingandsurveillancenetworkstoassessspatialandtemporalevolutionofdiseasesandimproveepidemiologicalmodels;(4)Takeananticipatoryandpreventiveapproachbasedonriskanalysiswhenaddressingdiseasemanagementinforestecosystems(evenmoresothanforcrops),avoidtotalrelianceononeortwocontrolstrategies(asHain[2006]recommendedwhendiscussingtheunsatisfactoryresultsofbalsamwoollyadelgidcontrolefforts),andanticipatesurprisesandthresholdeffects.

•Diseasemanagementoptionscouldbealtered(Coakleyandothers1999)orimposed.Forexample,althoughitisknownthatmovementoffirewood,nurserystock,andevenfamilytrailersandboatsisresponsibleforthetransportofmany


species,thereisnocohesivestrategyforaddressingthisproblem(Moserandothers2009).Otheractionsproposedformanaginginsectsanddiseasesinclude:

•Avoiddisseminationofpestsintoclimaticallyfavorablezoneswheretheycouldfindnaïvehostpopulationsbypracticingstricthygienemeasures,basedonthemostprobabledisseminationpathwaysoforganisms(inseeds,wood,andplants).

•Reducevulnerabilitytofuturedisturbancebymanagingtreedensity,speciescomposition,foreststructure,andlocationandtimingofactivities(Daleandothers2001).

• Increaselight,water,andnutrientavailabilitytotheuninfected/uninfestedtreesanddecreasesusceptibilitytopestattackbypracticingprecommercialthinning,sanitationremoval,orselectiveremovalofsuppressed,damaged,orpoorqualityindividuals(Gottshalk1995,Papadopol2000,WargoandHarrington1991).

•Underplantwithotherspeciesorgenotypesinforestswherethecurrentcompositionisunacceptableasasourceofregeneration(SpittlehouseandStewart2003).

• Shortenrotationstoreducetheperiodofstandvulnerabilitytoinsectordiseaseattack,andreplanttospeedtheestablishmentofbetter-adaptedforesttypes(Gottshalk1995;Parkerandothers2000).

•Usepesticidesinsituationswheresilviculturalorothermeansofpestmanagementareineffective(Parkerandothers2000);however,becausemorphologicalorphysiologicalchangesinthehostresultingfromincreasedcarbondioxideuptakecouldaffectuptake,translocation,andmetabolismofsystemicfungicides(Coakleyandothers1999),incorporateintegratedpestmanagementpractices.

•Expandandimproveexistingmonitoringeffortstoincludeanexpectedincreaseinthenumberofnew,introducedplantdiseases(Sturrock2007).

•Assistinthemigrationofforests,byintroducingcarefullyselectedtreespecies(includingusingbiotechnologytechniquesinsomesituations)inregionsbeyondtheircurrentranges,beingmindfulofthepotentialforunforeseenconsequences.

Withrespecttononnativeinvasivespeciesmanagement,Moserandothers(2009)recommendfivepriorities:(1)promotingeducationandawareness,(2)expandingearlydetectionandactivemanagementandintensifyingenforcementofquarantines,(3)buildingthecapacitytoincreaseunderstandingofandtreatmentsforNNIScontrol,(4)strengtheningthebasicforesthealthcurriculum,and,(5)encouragingcrossagencycollaborationandinvestment.

Althoughtheprocessofplanningandactingtoprepareforafuturemostprobablyaffectedbyclimatechangeisfraught

withuncertainty,notplanningandactingwilllikelyresultingreatereconomicandsocialdisruption.Successcanonlybeachievedifthoseinenvironmentallysensitivemanagementrolesarewellinformedandexercisetheirbestjudgment.

Thesingleconsistentthemethroughouttheliteratureonpestimpactsandclimatechangeisthatminimizingecologicalchange(anddisruption)requiresmaximumpossiblebiodiversity,eitherthroughasystemofprotectedrefugiaorbydirectadaptivemanagementforspecificcharacteristics.

Differingperceptionsofriskandadaptationmayleadtoincreasedtensionamongvariousgroups.Conflictingprioritiesandmandatescouldalsoleadtofutureproblems(LemmenandWarren2004).Inthesesituations,caremustbetakentoadoptadecisionmakingprocessthatidentifiesandevaluatesallissuesandemploysthebestecologicalscience.

kNoWleDGe AND iNFoRmATioN GAPS

Asshouldbeclearfromtheabovediscussionofcurrentknowledgeandfromourprojectionsofthefutureactivityofknownpests,hugeuncertaintydominatesthesubjectofpestmanagementandclimatechange,withsignificantgapsexistinginbaselineknowledgemakinganygeneralizedquantitativemodelingoffutureconditionsimpossible.Althoughsomespecificpestbehaviorshavebeenprojected,mostofthemarequalitative.Lackinggeneralizedandoftenspecificbaselinedataleavesmodeling(quantitativeprojection)adesiredtoolwhosetimehasyettocome.Currentlyunavailabledatathatwouldcontributetoageneralizedprojectionofpotentialfuturepestactivityinforests(Beukemaandothers2007;ChakrabortyandDatta2003;Hain2006;LemmenandWarren2004;Loganandothers2003;MamlstromandRaffa2000;Rogersandothers1994;Scherm2004;and,Seem2004)include:

Informationonhostbiologyandresponsetopests:theroleofchangingsecondarymetabolites(primarilyphenolsorphenol-like)underchangingenvironmentalconditions;thefunctionalcomponentsofrespiration(construction,maintenance,andionuptake)aswellascarboncostsduetorootexudation;theroleofwaterintreehealth;thegenotypicvariabilityandplasticityofhosts;waterbalancethresholdasitaffectsdirectmortalityofhostplants,theeffectsofclimatechangeonhostdefensivemechanisms(physiological,morphological,orother);theimpactofclimatechangeonbiodiversityandtheroleofbiodiversityinecosystemfunctionsandpestmanagement/prevention;and,projections


ofhostmigrationandavailabilityundertheinfluenceofclimatechange.

Informationonforestpests:currentdistributionsandrangesofpests;influenceofmycorrhizaeonplanthealthunderclimatechange;directandindirecteffectsofcarbondioxide,ozone,andUV-Bonrootsandroot-surfacemicroflorasundernaturalconditions;knowledgeofinsectsandpathogensfromoutsidetheareasuchasMexicanbarkbeetlesandvariousAsianinsects;mechanismsbywhichchangesincarbondioxideandprecipitationalterpestsurvival,growth,susceptibilityandinteractions

Informationtoaddclarityandspecificityonpest/hostinteractions:dispersalstructureanddistanceandinterconnectednessoftemperature,phenologyandpestpopulationgrowthrate;phenologicalrelationshipsamongtreesandpests;roleofclimateoninsectsandpathogensinrelationtoavailablewater;baselinedataonpestsofnaturalpopulationsthatidentifytheseparateofmultipleclimatevariablesandproblemstheycause(includingforecastsofepiphytoticsorepizootics,andevaluationstheroleofevolution);pest/predatorinteractionsandresponses,relationshipsamongclimate,pests,andtheirparasites;minimumandmaximumtemperaturepreferencesofpestsandpest/hostinteractionsandresponsetotemperatureextremes;protocolforidentifyingthe“drivers”thattransformnewinsectsanddiseasesintopests;disturbanceregimesandtheirinteractiveimpacts;and,synergiesamongfire,insects,andpathogens.

Modelsandmodelingprotocolsneeded:modelsthatincorporatelocalmeteorologicaldata;improvedspatially-explicitclimatepredictionsatfinerscales(averagedailypatternsandprojectedvariationsfromtheaverage);effectsofdown-scalingorup-scalingdatafromvariousmodelsandappropriatelinkingtoolsforincreasingtheaccuracyofthesepredictiveprocessestobemoreaccuratepredictors;functionalgroupratherthansingle-speciesmodels;and,predictivemodelsthatincorporatedataondisturbancesanddisturbanceimpacts.

Managementinformationneeded:anewprotocolforaddressingtheresearchneedsofinvasiveforestpeststhatinvolvesallstakeholdersinacoordinatedpartnership;andmanagementactionplansdevelopedinthefaceofno-analogvegetationsystemsandclimatechange.

AckNoWleDGmeNTS

OurappreciationisextendedtoChristopherAsaro,VirginiaDepartmentofForestry;MatthewP.Ayres,BiologicalSciencesDepartment,DartmouthCollege;FredP.Hain,DepartmentofEntomologyandFrankKoch,DepartmentofForestryandEnvironmentalResources,NorthCarolina

StateUniversity;EdwardL.Barnard,FloridaDivisionofForestry;RonaldF.BillingsandDonaldM.Grosman,TexasForestService;ScottCameronandJamesJohnson,GeorgiaForestryCommission;StephenR.Clarke,JohnA.Ghent,WilliamE.Jones,BruceD.Moltzan,DerekPuckett,JamesD.Smith,DaleA.Starkey,andBorysM.Tkacz,ForestHealthProtection,SusanJ.Frankel,PacificSouthwestResearchStation,andKierKlepzig,AlbertE.‘Bud’Mayfield,III,DanielMiller,WilliamJ.Otrosina,andA.DanielWilson,SouthernResearchStation,U.S.DepartmentofAgriculture,ForestService.

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andallvegetation.Newplantcommunitieswillorganizethemselvesandwillreplaceplantsthatareunabletoadapttonewclimates.Newcommunitiescouldincludecurrenttreespecies,othertreespecies(e.g.,hardwoodsorstronglydispersingspeciesfromwarmerareas)orcouldbecomedominatedbygrassandshrubspecies.

moDeliNG climATe chANGe

Available models

Majoreffortsareunderwaytocreateandusemodelsthatcanprojectpotentialscenariosdescribingboththeimpactsofclimatechangeonecologicalconditionsandthesubsequentresponsesresultingfromandpossiblytheninfluencingthoseconditions.Modelingcancontributetoourprojectionsoffutureconditions“…butrequiressoundknowledgeofthecausalfactorsdeterminingspatialdistribution,survival,reproduction,dispersal,andinflictionofdamage”(GoudriaanandZadocks1995).

Selectionofbroad-scalemodeltypes(suchasgeneralcirculationmodels,process-basedmodels,andempiricalmodels)dependsonthespecificquestionsbeinganalyzedandtheavailablerelevantdata.Theapplicationofgeneralcirculationmodelsislimited;thefinestscaleusedforglobalclimatesimulationisfartoocoarseformeaningfulecologicalapplications(Loganandothers2003).Atasmallerscale,gapmodels,biogeographymodels,andbiogeochemistrymodelsareamongthosebeingusedtorefineprobablebroad-scalemodelprojectionstoreflectconditionsatamorelocalscale(Winnett1998).

Currentmodelprojectionsoffutureconditionsthatwillaffectforestcompositionandproductivityvaryoverawiderangeofplausiblescenarios(Loganandothers2003,NationalAssessmentSynthesisTeam2000,Scherm2000).

Scherm(2000)supportsMillstein’s(1994)contentionthatuncertaintiesinmodelinputcancompromisethecredibilityoftheoutputbecauseoferrorperpetuationorpropagation.Thesescientistsarenotaloneintheirconcern.Othersaddtheconcernthatdataselectioncanalsosignificantlyinfluence

iNTRoDucTioN

Thisappendixcontainsageneralizedsummaryoftherelevantliteraturerelatedtoclimatechange,vegetationchange(speciesandgeographicrangechanges),andpestactivityscenarioclassificationasreflectedinthecurrentliterature.

Informationforthisappendixwasderivedfrompublishedscienceliterature,alongwithaselectionofliteratureaboutthebiologyandecologyofforestpests.AdditionalinformationaboutforestpestsandtheircontrolisreadilyavailablefromStateandFederalforestryagenciesoronline(twogoodstartingpointsarehttp://na.fs.fed.us/pubs/index.shtmandhttp://www.fs.fed.us/r8/foresthealth/).

Manyscientistsbelievethatclimatechangeintheformofglobalwarminghasoccurredoverthelastcenturyandwillcontinuetooccurintotheimmediatefuture(IntergovernmentalPanelonClimateChange2007,Kleijunasandothers2009,MalcolmandPitelka2000,McNultyandAber2001,NationalAssessmentSynthesisTeam2000).Theprimaryfactorsofclimatenotedasdrivingobservedecologicaleffectsaretemperatureandavailablewater.Inadditionatmosphericgasses(carbondioxideandairpollutantssuchasnitrogenoxidesandsulfurdioxide)inexcessoftheir‘normal’rangesareoftenidentifiedasadditionaldriversofthechangebeingobserved.Climatechangeisalsolinked,atleastinpart,tohumanactivity(MalcolmandPitelka2000,Sturrock2007,Winnett1998).Thesechangesareexpectedtoimpactcropsandtheirpestsindividually,aswellasimpactingtheinteractionsbetweencropsandpests(Runion2003).

Reportingtheresultsofaworkshopattemptingtounderstandthepotentialinteractionsamongforests,insects,diseases,andclimatechange,Beukemaandothers(2007)reportthat:

Participantsagreedthatthingswillchange.Mostvegetationcommunitieswillnotsimplymigratefromonelocationtoanother.Instead,manycommunitieswillbecompletelynew,withnewcombinationsoftrees,understoryplants,insects,anddiseases.Atthesametimeitisimportanttobearinmindthatwearenotgoingtocompletelyloseallforests

appeNDIX C. climate change and its impacts on Forests


modeloutput.Theuseofacrispdatasetversusa“fuzzynumber”setwillhaveadditionalmajorimpactsonoutputs(Coakleyandothers1999).

SchermandCoakley(2003)haveidentifiedthreecontinuingproblemswiththeapplicationofmodelsforpredictingclimatechangeeffects:

• Modelinputshaveahighdegreeofuncertainty.

• Nonlinearrelationshipsandthresholdsintherelationshipbetweenclimaticvariablesandepidemiologicalresponsescomplicateeffortstocollectsufficientdataforclearpredictiveunderstanding.

• Modelingoftenignoresthepotentialforadaptationbyplantsandtheinsectsanddiseasesthatattackthem.

Physical impacts of climate change

Temperature—Increaseinaveragetemperatureisconsistentlyshowninresultsfromavarietyofmodelsasbeingofconcern.TheIntergovernmentalPanelonClimateChange(2007)statedthatthedatasupportinganongoingwarmingoftheclimateareunequivocal,pointingtoobservationsofincreasesinglobalairandoceantemperatures,widespreadmeltingofsnowandice,andrisingsealevels.Thepanelfoundalineartrendinaveragetemperaturewhichhadincreasedby0.74ºC(0.56to0.92ºC)from1906to2005,higherthantheearlierreportedincreaseof0.6ºC(0.4to0.8ºC)for1901to2000(IntergovernmentalPanelonClimateChange2001);thatlandareashavewarmedfasterthanoceans;andthattemperatureincreasesappeartobelargerinnorthernlatitudes.

Overall,climatechangeispredictedtoleadtoincreasingtemperature.Meanglobalsurfaceairtemperaturesarepredictedtoincreasefrom1.4to5.8ºCbytheendofthecentury.Bothnight-dayandwinter-summeraveragetemperaturerangesarelikelytoshrinkasminimumtemperaturesincreasemorethanmaximumones,andcontinentalandhigh-latitudeareaswilltendtowarmmorethancoastalandlower-latitudeareas(Burdonandothers2006,Harvellandothers2002).Themagnitudeofthesechangesisexpectedtovarybothtemporallyandspatially(McNultyandBoggs2010).

Water regime—Waterisreportedtobeofgreatsignificance,secondonlytotemperature,whenprojectingpotentialeffectsofclimatechange.Overabundanceofwater,lackofit,andseasonalityofitsavailabilityallhavesignificantimpactsontheforestprocessesthatgoverntheoverallhealthofindividualorganisms.Projectionsofoverallresponsestorainfallpatternvarygreatly.Generalizationsfoundintheliteratureincludethefollowing:

• IntheSouth,intenseprecipitationeventshaveincreasedoverthepast100years(NationalAssessmentSynthesisTeam2000).

• Risingsealevelshavealreadyhadsignificantimpactsoncoastalareas,andtheseimpactswilllikelyincrease(NationalAssessmentSynthesisTeam2000).

MalcolmandPitelka(2000)summarizedtheeffectsofwaterasfollows:futureregional-scaleprecipitationchangesremainparticularlydifficulttopredict,andchangesinthefrequencyandseverityofstormsandotherextremeweathereventsareuncertain(Wigley1999).Overallthesechangeswillappearasashiftofclimaticzonestowardsthepoles;warmertemperatureswillreachfurthernorthintheUnitedStates.Thislastobservationintroducesacriticalconcernwhendiscussingclimatechange.Ecologicalfactorsdonotfunctioninisolation,theyinteractandinfluenceeachother.Thisisafacteasilyforgottenwhenreadingtheliterature,muchofwhichdiscussessinglefactoreffectsatavarietyofscales.

Carbon dioxide and trace gases—Carbondioxideisroutinelycitedasaprimarycauseofglobalwarming.Theconsensuswithinthescientificcommunity(Coakley1988)isthattheincreaseincarbondioxideandshiftingpercentageoftracegases(ozone,chlorofluorocarbons,nitrogenoxides,sulfuroxides,andmethane)willcombinetobringaboutcontinuingglobalwarming.Althoughthisisgenerallyagreedtobeanaccurateprojectionoffuturecondition,thespatialrelationshipsinvolvedareextremelyuncertain,asarepredictionsofwheretheeffectwillbesignificant.

Light—Solarradiationisthesourceofenergyformostterrestrialprocesses,andanythingthatalterstheamountofradiationreachingtheearth’ssurfacemayalterclimate.Fluctuationsinsolaroutput,volcaniceruptions,andothernaturalperturbationsinfluencesolarinputtotheearth’senergyengine,asdochangesinlanduseandindustry.Thequalityoflightandthedurationofphotoperiodhavebeenshowntoaffectplantsinavarietyofways.Yetexcepttonotethatgreenhousegassescanaffectthequalityoflight,littleissaidintheliteratureaboutpossiblefutureshiftsinlightquality.Photoperiodisseldomdiscussedaschangingforagivenarea.Effectsofphotoperiodonlyappeartobenotedassignificantwithinthecontextofotherfactorsthatinfluenceplantmigrationsasdescribedbelow.

Wind—Intheearly1950s,Hepting(1963)foundthatwind,nottemperatureorrainfall,wastheprimarydriverofclimatechangeinGreatBritain.Morerecently,LemmenandWarren(2004),alsodiscussingclimatechangeinGreatBritain,suggestthatawarmerclimatemaybemoreconducivetoextremewindeventsandthatthesemayinturnhaveconsequencesforotherforestdisturbances.Yarwood(1959)suggestedthatwindhassignificantimpacts,both


directlyorindirectly,onplantsandthepeststhatattackthem.Unfortunately,withtheexceptionofdiscussionsinthecontextofstormevents,windislittlediscussedintheliterature,andwefoundnoprojectionsoffuturewindeventsintheSouth.

Soil—Soilchemicalpropertiesdonotappeartobedirectlyaffectedbyclimatechange,theironlycontributiontoclimatechangebeingacomplexofsecondaryeffects.However,itisgenerallyrecognizedthatasairtemperatureincreasessodoessoiltemperature.Soilwarminginconjunctionwithdroughtisamajorconcernbecauseitpredisposesrootsandrootletstomortality,whetherornotrootrottingfungiareinvolved.Localizedandoftenshort-termshiftsinthealbedoarepredictedifsoilwarmingresultsinthefailureofvegetativecover,butpredictionsarenotspatiallyexpliciteitherastosizeorlocation.

Ratesofsoilmineralization,acidification,nitrification,andcarbonsequestrationareallprocessesthatareclearlyinfluencedbyclimatechange,butgenerallytheseeffectsaremoreaffectedby(andsubsequentlyinfluence)thelocalbiota.

Mixed edaphic effect projections—Avarietyofprojectionshavebeenmadeforcompoundededaphicfactors;fourarebrieflynotedbelow:

• Increasedfrequencyofextremeweatherevents(Scherm2003)

• Increasedfrequencyandintensityofdroughtoccurringunderwarmertemperatures(Breshearsandothers2005)

• Morefrequentwinterwaterloggingresultingfromincreasedwinterrainfall(BroadmeadowandRay2005)

• Increaseddurationofsunshineresultingfromchangesintemperatureandhumiditywhichinturnleadtoreducedsummercloudcover(BroadmeadowandRay2005)

imPAcTS oN PeSTS AND iNDiViDuAl hoST PlANTS

Climateisthesinglemostimportantfactordeterminingthedistributionofmajorvegetationtypesandindividualspecies(MalcolmandPitelka2000).

Extrapolatingthephysicaleffectsofclimatechangetothepotentialbiological/ecologicaleffectsthattheyengenderisoftenproblematic.Thesimpledescriptionisthatastheclimatewarms,southernforestswillmigratenorthwardandupward(assumingthathigherelevationsitesbecomeavailable),andwilldisplaceaportionofthetemperatemixedhardwoodforest.Thetemperatemixedhardwood

forestinitsturnwillmigrate,displacingpartofthenorthernborealforest.Althoughthispresentsaneasytounderstandgeneralization,itmasksanextremelycomplexreality.

Forestsarenotexpectedtomigrateascohesiveunits.Althoughdrivenbyasetofindividualphysicalparameters,migrationwillmorelikelyresponddirectlyatthespeciesandindividualplantlevel,notattheassociation,ecosystem,orotherecologicalleveloforganization.Differentspecies(anddifferentindividualsevenwithinaspecies)willreactinpotentiallyverydifferentwaystothevariousstimuligeneratedbyclimatechange.Theresponsesofecosystemscanonlybepredictedbyunderstandingthebehavioroftheirconvergentpropertiesandtheuniquecharacteristicsandresponsesofindividualspecies(MalcolmandPitelka2000).

Onthepositiveside,increasinglysophisticatedcomputermodelshavebeendevelopedthatincorporatemorefundamentalecologicalmechanisms.However,eventhesenewermodelscannotyetpredictwithaccuracywhathappensastheclimateischanging(MalcolmandPitelka2000).

Nevertheless,wehavesomeclearreportsofobservedresponsestoclimatechange.Anaverage1°Cincreaseinaveragetemperatureisreportedtoincreaseplantgrowthandlengthenthegrowingseason.Budbreakofquakingaspen(Populustremuloides)isreportedtobe26daysearlierthanacenturyagoinAlberta,Canada;andbudbreakofwhitespruce(Piceaglauca)isearlierinOntario(LemmenandWarren2004).Ground-basedmonitoringeffortsinEuropedocumentedan11-dayincreaseingrowingseasonlengthovera34-yearperiod(MalcolmandPitelka2000).Becausetemperaturecanaffectecosystemsinmanydifferentwaysandbecausetherearemultiplepathwaysforfeedbackandinteraction,evaluatingorpredictingtheeffectsoftemperatureincreasesisnotsimple.Notsurprisingly,publishedresultshavebeenmixed(MalcolmandPitelka2000).

Thesizeofplantorgansatmultiplescalesmayincreaseasaresponsetoelevatedlevelsofcarbondioxide.Increasedareaperleaf,leafthickness,numberofleaves,leafareaperplant,anddiameterofstemsandbrancheshaveallbeenobservedunderincreasedcarbondioxide.Enhancedphotosynthesis,increasedwateruseefficiency,andreduceddamagefromozonearealsoreportedasresponsestoincreasedcarbondioxide(Garrettandothers2006).

Disease and insect Risks, Absent climate change

ThesecondperiodicNationalInsectandDiseaseRiskMap,completedin2006,presentsastrategicassessmentofpotentialtreemortalityresultingfrommajorinsectsanddiseases.Thisisthedefinitivesourceatthepresenttimeforprojectedinsect-anddisease-causedmortality


Zadocks1995).Althoughthenumberofrecentattributionsofpathosystemshiftsresultingfromclimatechangeisincreasing,fieldresearchisplaguedbythelong-termnatureofclimatechange,whichismuchmorecomplicatedthantheshiftsinweatherthathavebeenmorecommonlystudiedinthepast(Coakley1988).

Host-pestinteractionswillbeaffectedbyclimatechangeinsimilarwaysasotherplantsandanimals.Inthemostsimplisticscenario,pestspeciesmigrationswillgenerallyfollowthemigrationoftheirpreferredhosts.Allofthesameecologicalelementsaffectingthehostsinthenewenvironmentwillimpactthepeststhemselves.Temperature,availablewater,qualityanddurationoflight,airquality,soilcondition,andotherfactorswillaffecttheirphysiologicalandecologicalresponses.Inaddition,theconditionandpossiblyalteredphysiologyofthehostinitsnewenvironmentwillinfluencethenewhost-pestinteraction.

Diseaseevolutionisanotherfactorthatpresentscomplicationswhenpredictingthemigrationofdiseasesintonewareas;ratesaredeterminedbythenumberofgenerationsofreproductionpertimeinterval,alongwiththeheritabilityoftraitsrelatedtofitnessunderthenewclimatescenario(Garrettandothers2006).

Afewrecentpublicationshavefocusedontheneedtoconsidermicroclimatefactorsasbeingimmediatelyrelevantwhendescribingpest-hostinteractions.Thisisalittlestudiedareaduetothecomplexityinherentinisolatingmicro-effectsinamacro-scaleecosystem.

Temperature effects on diseases—Gradualwarmingwouldprobablyleadtoageneralnortherlyshiftinseasonalclimaticregimes,whichinturnwouldaffecttherangeofoak(Quercusspp.),sometimesadverselyandsometimesfavorably(BrasierandScott1994).Newdiseasecomplexesmayariseandsomediseasesmayceasetobeeconomicallyimportantifwarmingcausesapolewardshiftofagroclimaticzonesandhostplantsmigratebeyondtheircurrentranges.Pathogenswouldfollowthemigratinghostsandmayinfectremnantvegetationofnaturalplantcommunitiesnotpreviouslyexposed(Coakleyandothers1999).

Thegeographicrangeoffungalpathogensaretosomeextentdeterminedbythetemperaturerangesoverwhichtheycangrow(LonsdaleandGibbs1994).BrasierandScott(1994)foundthatthegrowthanddevelopmentofmanyfungiwithinthehostmayoftenbefavoredbyclimatewarming,andtheconditionsthatprevailwhenfungiarriveatthehostsurfaceareoftencriticalfordiseaseestablishment;theyalsoobservedthattheeffectsoftemperatureonthedevelopmentandpopulationdynamicsofmanypotentialoakdiseaseshavebeenlittleresearchedandtheyidentifiedthedifficultiesinvolved.Nevertheless,theypredictedthat

aswarmingincreasesinEurope,arootrotdisease(causedbyPhytophthoracinnamomi)willextenditsnorthwardrange,survivewintersbetterinrootsystems,showincreasedspreadwithinthehost,havegreaterinfectionfrequencyofnewhosts,andcausemarkedlymorerapidhostdeclineandmortality.

OtherauthorsconcurwiththepredictionsofBrasierandScott(1994).Chakrabortyandothers(1998)pointoutthatchangesintemperaturewillalterhost-plantphysiologyandthushostresistancetopests.BroadmeadowandRay(2005)addthatincreasedtemperatureswillresultinhigherevapotranspiration.AndBurdonandothers(2006)reiteratethatwhenweturntotheimpactofthemoreunpredictableaspectsofglobalclimatechangeonthepathogensthemselves,wewilllikelyseesignificantchangesinhost-pathogeninteractionsovertime,whicharelikelyinbothdirections(increaseanddecreasedactivity).

Increasedsoiltemperaturehasbeenshowntohavenegativeeffectsonplantroots.Redmond(1955)reportedthatina55-yearoldstand,yellowbirch(Betulaalleghaniensis)rootletswithanormalbackgroundmortalityrateofabout6percentsuffered19percentrootmortalitywhenaveragesoiltemperatureincreased1°Cand60percentrootmortalityifthetemperatureaverageincreased2°C.Theyalsoreportedachangeinmicrobialpopulationandachangeinthedevelopmentofmycorrhizae,thesymbioticassociationsbetweenfinefeederrootsofplantsandroot-inhabitingfungi.

Becauseoftheirrapidresponsetosmallenvironmentalchanges,pathogensmayprovidegoodearlywarningofimpendingclimatechange.Thedamagethresholdfromadiseasemayalsochangeinanewgeographicallocation(Chakrabortyandothers1998).

Temperature effects on insect pests—Higherairtemperaturescommonlyenhancethegeneralactivity,populationsize,andpotentialfordispersalofinsectpests.Highertemperaturescouldleadtogreateroverwinteringpopulationsize,increasedlengthofflightseason,andlengthofdailyflightperiods(BrasierandScott1994).Continuedclimatechange,andparticularlywarming,wouldhaveadramaticimpactonpestinsectspecies.Ascold-bloodedorganisms,theyhavealifehistorythathingesontemperature;thermalhabitatlargelysetstheboundariesoftheirgeographicdistribution(Loganandothers2003).

Extendedperiodsofwarmweathercanfavorthedevelopmentofinsectpestsbothdirectlyandindirectly.Warmtemperaturescanacceleratethedevelopmentofinsectpopulationsbyreducingthetimeneededforlife-cyclecompletion.Indirecteffectscanbetheresultofchangesinthehostplant,orcanbeproducedbydecouplingrelationshipswithnaturalenemies(MamlstromandRaffa


2000).Insomecircumstances,warmertemperaturescouldactuallyinhibitinsectactivityordisruptthebuildupofpopulations:althoughwarmerwinterswouldincreaseoverwintersurvivalofsomeinsectpests,reducedsnowcovercouldincreasethewintermortalityofothers(Burdonandothers2006).Enemiesofinsectpestswouldalsobeaffectedbyclimatechange,buttheseeffectsaregenerallyunknownandrequiremoreresearch.Ifwarmertemperaturesfavorpredatorsandparasitoids,thesenaturalenemiesofpestswillexhibitgreatercontrolofthosepestspecies.Conversely,ifwarmertemperaturesdisruptordecreasepredatorandparasitoidpopulations,pestpopulationswillgrowmorequicklyandwillpersistathigherlevelsforlongerperiodsoftime.

Available water effects—Gilmour(1960)identifiedtwooppositewaterrelatedconditionsthatcausesignificantimpactsontrees.Droughtconditionshavebeenshowntobethecauseofvariousdisorderswithorwithoutanyassociatedfungalpathogen.And,saturatedsoilhasbeenfoundtocausedisordersinmanyplants.Thus,bothextremesinwateravailabilityhavebeenshowntonegativelyaffecttrees.Saturatedsoils,althoughbeingsomewhatdeficientinoxygen,appearalsotohavealteredchemistryfromsimilardriersoils.Garrettandothers(2006)foundthatevenwithouttheaddedimpetusofclimatechangetheinteractionofprecipitationanddiseaseisofprimaryimportanceforpredictingdiseaseseverity.

BroadmeadowandRay(2005)foundthatincreasedwinterrainfallleadstomorefrequentwinterwaterloggingofsoiland,insomecircumstances,tofinerootdeathextendingintothesoilsurfacehorizons.Thisinturnexacerbatestheeffectsofsubsequentsummerdrought.Blackandothers(2010)associatedSwissneedlecastdisease(Phaeocryptopusgäumannii)withspringandsummerneedlewetness,aswellaswintertimetemperatures.

Becausemostplantparasiticfungiarebelievedtorequirefreewaterforsporegermination,microclimateofleafsurfacesisanimportantconsideration.Theimportantsourcesoffreewaterforfoliagediseasesarerain,fog,condensedwater,andguttationwater.Yarwood(1959)foundlittlegerminationwhentherelativehumidityfellbelow95percentandcategorizedfoliagediseasesbytheirrequirementsforwaterinthephyllosphereduringtheinfectionstage;but,insteadofpresentingabroadcategorizationofthiseffect,focusedattentiononrustfungi(specificallytheirurediosporestage).

LemmenandWarren(2004)emphasizethatforestcharacteristicsandage-classstructurealsoaffecthowforestsrespondtochangesinmoisture,notingthatmatureforests(withwellestablishedrootsystems)arelesssensitivetochangesinmoisturethanyoungerforestsand

post-disturbancestands—atleastintheshortrun.Theyaddthatdifferentspecieshavedifferentdroughttolerance,whichalsomustbeconsidered.AndLonsdaleandGibbs(1994)remindusthatclimatechangewithitsassociatedchangeinfrequencyofsummerdroughtswouldalterthestabilityofassociationsbetweentreespeciesandvariousmembersoftheirnon-diseasefungalassociations—resultinginanoutbreakofdiseaseinplaceofcoexistence,orinsomecircumstancesmutualism.

Hansonandothers(2001)foundthattheimpactofpotentialchangesindroughtorprecipitationregimeswillnotonlydependonthepredictedscenarioofchange,butalsoonthetypeofforestecosystemandtheclimateconditionstowhichitiscurrentlyadapted.Theyconcludebysummarizingsixreasonswhyforestswouldnotexhibitcatastrophicdiebackundertheinfluenceofclimatechange(includingdrought)andthepredictionthatthereplacementofforestsbyfastergrowingtreeswillbegradual(Loehle1996).

Generallyspeaking,anyprecipitationregimethatstresseshosttrees(whetheritistoolittleortoomuchmoisture)willmakethemmoresusceptibletoinsectattack.

Wind effects—Yarwood(1959)citeswindasbeingaseriousmodifierofwaterrelationsandsuggeststhatwindcommonlypreventstheformationofdew,andcausesraindropsordewtoevaporatemorerapidlythantheywouldinstillair.BroadmeadowandRay(2005)notethatanincreaseinthenumberofstormsmaymakewoodlandsmorevulnerabletowinddamage.

Light effects—Fungipreferentiallygrowwhentheskyiscloudyandarethereforeactivemainlyonshadedpartsoftheplantorinnon-irradiatedanglesoftheecosystem.Pathogenicfungiareadditionallyprotectedwhengrowingpartlyorcompletelywithinthehost’stissue(ManningandvonTiedemann1995).

Thegreatsignificanceoflightespeciallyinthenearultravioletband(UV-A)onfungalsporulationhasbeenrecognizedsincethefirststudieswereperformedonthisphenomenoninthe1960s.Humphrey(1941)reportsthatexposuretolightstimulatedsporulationin62of75speciesoffungitested;mostrequiredlightfortheinitiationofsporulation.Sporulationwasnotinhibitedinanyofthe417fungalstrainstestedwhenexposedtolight.However,enhancedUV-Bradiationmayincrease,decrease,orleaveunaffectedtheseverityofbioticdiseases.Aseriouscomparisonofthiscontradictoryinformationisnotpossiblesince,intheunderlyingstudies,therangesoflightqualities,lightintensities,andlightexposuresweretoolargeandtoovariableasweretheexperimentaldesignsandtimecoursesapplied(ManningandvonTiedemann1995).


Ifsomepartsofthediseaselifecyclearephotoperiodsensitive,populationsmightneedtoundergoextensiveadaptationtomakeuseofextendedseasonsintemperateareas(Garrettandothers2006).

UV-Bhaspositiveandnegativeeffectsonfungaldevelopment;itseffectondiseasesismainlythroughalteredphysiologyandmorphology(Chakrabortyandothers1998).

Air quality effects—Asnotedabove,increasedcarbondioxideintheatmosphereisgenerallycitedasbeingaprimaryfactorindrivingphysiologicalchangesinplantpopulations.Workingwithapasturelegumeandafungus(Coletotricumgloeosporioides)attwotimesambientcarbondioxideconcentration,Runion(2003)reportedanincreaseofvirulenceofthediseaseagainstresistantcultivarsofthelegume(nochangewithrespecttosusceptiblecultivars)andasignificantincreaseinfecundity(morepronouncedintheaggressivefungalcultivarsbeingtested).ChakrabortyandDatta(2003)focusedparticularconcernonwhetherthisincreasedfecundityatelevatedcarbon-dioxidelevelscouldrapidlyerodetheusefulnessofdiseaseresistance.Alteringthepredispositionofthehosttodiseasemaybethepredominanteffectofrisinglevelsofcarbondioxide(ManningandvonTiedemann1995).

Charkrabotoryandothers(1998)reportanincreaseofdiseaseseverityinresponsetoincreasedcarbondioxidefor6of10biotrophicfungiand9of15necrotrophicfungi;andobservethatpredictingeffectsforunstudiedpathosystemswillbechallenging,andevenmorechallengingwhenincludingthecombinedeffectsondiseasesandtheirhostplants.

Burdonandothers(2006)suggestthattheeffectofcarbondioxidemaybetoincreasetheefficiencyofcarbonfixationwitharesultantincreaseingrowthandimprovementinthecarbonstatusoftheplant.Thisincreasewouldleadtomorphologicalchangegenerallyexpressedasenhancedgrowth;thecombinedchangesinnutritionandmorphology,inturn,couldaffectthesuitabilityoftheplantashostmaterialforavarietyofdiseases.Thishavingbeensaid,theauthorscautionthatthereportedresearchonthesubjectislimitedandendthediscussionwiththisfurthercaution:“…thepredictabilityoftheimpactofthesefactorsasonwholecommunitiesisevenmoreuncertainwithbothindirectanddirecteffectsofvaryingmagnitudebeinglikely.”

MirroringthisconcernLemmenandWarren(2004)reportthatalthoughnumerousstudieshaveinvestigatedtheimpactsofelevatedcarbondioxideonforestgrowthandhealth,theresultsareneitherclearnorconclusive.

ManningandKeane(1988)concludethat“inatheoreticalsense,airpollutioncanincrease,decreaseornotaffectthe

courseofdevelopmentofadiseaseepidemic,”basedonnewandexistingobservationsaboutairpollutionandpestbehaviorincluding:

• Bacterialdiseasesaregenerallyinhibitedbysulfurdioxide,whichlimitslesionsizeandoftenincreaseslatentperiods.

• Fungaldiseaseshavebeenreportedtobeenhanced,inhibited,ornotaffectedatallbyairpollutants.

• Thelittlethatisknownabouttheeffectsofpollutiononrootdiseasesindicatesthatvirus-affectedplantsareusuallylessaffectedbyairpollutantsthanvirus-freeplants.

• AccordingtoJamesandothers(1980a),inoculatedstumpsofozone-stressedpines(Pinusspp.)weremorereadilyinvadedbyannosumrootdisease(causedbyHeterobasidionannosum).

• AccordingtoSkellyandothers(1983),ozonestressedeasternwhitepine(Pinusstrobus)intheBlueRidgeMountainsofVirginiaweremoresubjecttoLeptographiumrootdisease(causedbyVerticicladiellaprocera).

• AccordingtoMahoneyandothers(1985),loblollypineseedlingswithectomycorrhizae(Pisolithustinctorius)werenotadverselyaffectedbyozone,sulfurdioxide,oracombinationofboth.

• AccordingtoKeaneandManning(1987),ozonecausedsignificantdecreasesinectomycorrhizaeofwhitebirch(Betulapendula)andwhitepineseedlings.

Soil environment effects—Carbondioxideconcentrationinsoilisexpectedtobefarlessimpactingtodiseasesthanatmosphericcarbondioxide.Soilmicrofloraisroutinelyexposedtolevels10to20timeshigherthanatmosphericcarbondioxidelevels(Coakleyandothers1999;ManningandvonTiedemann1995).Colonizationandpersistenceofmycorrhizaeappearstobedependent,inpart,onthenutrientstatus(primarilynitrogen)andcarbondioxideconcentrationinsoil,althoughobservedresponsesdonotshowaconsistentpattern.Notmuchmorecanbesaidherebecausetheinfluenceofmycorrhizaeonplantdiseaseisstillnotwellunderstood.

Ozonedoesnotpenetratethesoilsurfaceandthereforeaffectsrootsonlyindirectlybyalteringphotosynthesis.Damagecausedbyseveraltreerootdiseasepathogensbecamemoreseverewhenthehostplantwasstressedbyozone(Fennandothers1990;Jamesandothers1980b,1982;Skellyandothers1983).


O’Neill(1994)presentsadetailedreviewofthepotentialeffectsofelevatedlevelsofcarbondioxideontherhizosphere(theregionofsoilthatisdirectlyinfluencedbyrootsecretionsandassociatedsoilmicroorganisms),observingthatecosystemsarelargelyconstrainedbytheratesatwhichsoilprocessesoccur.Muchmoredatawillbeneededtobegintheprocessofgeneralizedmodelingofeffectsontherhizosphere.

Effectsofsoilsaturationhavealreadybeenbrieflydiscussedabove.Boththeamountofwaterandtimingoffloodingaffectthedegreeofnegativeimpactoncoverplants.

Soilcharacteristics,nutrientavailability,anddisturbanceregimesmayprovetobemoreimportantthantemperatureincontrollingfutureecosystemdynamics(LemmenandWarren2004).Climateandvegetationinteracttodeterminethecharacteristicsoilsofanarea,anddifferentclimaticzonesarecharacterizedbydifferentsoiltypes—exceptwherethepresenceofunusualrock,suchasserpentine,resultsinuniquesoils(MalcolmandPitelka2000).

effects on host Biology

Littleisknownabouthowenvironmentaleffectsontreephysiologyinfluencetheinducibleresponsesthatarerelevanttopathogens(signalrecognition,generationofphytoalexinsandreactiveoxygenspecies,hypersensitiveresponses,callusgrowth,andsystemicacquiredresistance)(AyresandLombardero2000).

Carbondioxideisaprimaryinputtogrowthanddevelopmentofallplantlife,providingbothafertilizationeffectandanincreaseintheefficiencywithwhichplantsusewater.Thefertilizationeffectmaybeaffectedbytheavailabilityofwaterandothernutrients.Itmayalsodiminishafteraninitialperiodofadjustmentbytheplant.Increasedcarbondioxidelevelsmayalsotriggerchangesinthechemicalcompositionofvegetationsuchasaffectingthecarbon-to-nitrogenratioinleaves(Winnett1998).Positiveresponsetocarbondioxideappearstooccurunderawiderangeofnutrientavailability(Rogersandothers1994).Inaddition,Bazzazandothers(1994)stressthatthedifferentialresponsesofspeciestoelevatedlevelsofcarbondioxideindicatepotentialshiftsinthecompetitiverelationshipsamongplants.Partialclosureoftheguardcellsformingstomateshasbeenproposedasthemechanismbywhichplantsslowtranspiration(JonesandMansfield1970),whichinturnmaybeonemechanismofadaptiveresistancetoelevatedcarbondioxidelevels.

Otherfactorstoconsiderincludethefollowing:

• Insoils,somefungicanusecarbondioxideasanadditionalsourceofcarbon,whichisincorporatedinto

organicacidsandeventuallyenterstheKrebscycleasanadditionalenergysupply(ManningandvonTiedemann1995);thisincreasetendstoincreaserootgrowthmorethanabovegroundgrowth(Rogersandothers1994).

• Ozoneeffectsonplantdiseasesarehostmediated.

• TheprincipalmechanismforUV-Beffectsonplantdiseaseswouldbethroughalterationofhostplants(ManningandvonTiedemann1995).

• Host-pathogenrelationships,defenseagainstphysicalstressors,andthecapacitytoovercomeresourceshortagescouldbeimpactedbyrisesincarbondioxide(Rogersandothers1994).

• Duringwinterdormancy,directeffectsofclimateonthehostaregenerallylessimportantthanthoseinvolvingapathogen(LonsdaleandGibbs1994).

combined effects

Increasedsummertemperaturesanddroughtinesswouldbeexpectedtohelpshiftthedistributionsoffunginorthwardswithintherangeofpotentialhosts,oratleasttoincreasethegeographicrangeoverwhichtheybehaveaspathogens(LonsdaleandGibbs1994).

Fungiappeartobelargelytolerantofcurrentozonelevels.However,astrongnegativecorrelationexistsbetweenrainfallorrelativeairhumidityandphotochemicalozonegenerationintheatmosphere:onwetdaysthatareappropriateforfungalgrowthonplantsurfaces,ozonelevelsareusuallylow.Consequently,biologicallyharmfulconcentrationsofozoneareunlikelytocoincidewithgerminatingsporesoractivelygrowingmycelium(ManningandvonTiedemann1995).

Expectedincreasesingrowthfromelevatedcarbondioxidelevelswillalmostcertainlyaggravateproblemswithdiseases.However,thiseffectwouldlikelybeoffsetbygrowthreductionscausedbyincreasedozoneandUV-B(ManningandvonTiedemann1995).Becausecarbondioxidemaygreatlyalterecosystemstructureandfunction(BazzazandFajer1992),unmanagedforestecosystemsmaybeseriouslyimpactedbycarbondioxideactingincombinationwithdrought,comparedtointensivelymanaged,monoculturetreefarmswherespeciescompositionhasbeenaltered.Overalltheinteractionofcarbondioxideandtemperatureisnotwellunderstoodandtheexperimentaldatahavebeeninconsistent(Rogersandothers1994).

Athighertemperatures,anincreaseintheavailabilityofallmajornutrients(nitrogen,phosphorus,calcium,magnesium,potassium,andsulfur)canbeexpectedasaresultof


increasedwaterfluxesthroughsoilandhigherorganicmatterdecompositionrates,whichwouldincreasethecirculationofnutrientsinthesoil-nutritionsystem.Also,nutrientcirculationwouldincreasebecauseofhighergrowthratesofforestspeciesatincreasingatmosphericcarbondioxideconcentrationandwarmertemperature(Nilsonandothers1999).

Stressedtreesaremoresusceptibletoinsectpestsanddiseases(BroadmeadowandRay2005),enablingsomelevelofassessmentbyforestpathologistsandentomologists.However,firmprojectionsoffuturepestactivitycannotbemadeandconsiderablecautionshouldbeexercisedinextrapolatinganalysistoafutureclimate.Forsomeinsectsanddiseases,likelytrendscannotbepredictedevenonthebasisofexpertjudgment(BroadmeadowandRay2005).

Climatechangewilldirectlyinfluenceinfection,reproduction,dispersal,andsurvivalamongtheseasonsandothercriticalstagesinthelifecycleofadisease(CoakleyandScherm1996).Observedoutcomesincludemodificationsinhostresistance,alteredstagesandratesofdiseasedevelopment,andchangesinthephysiologyofhost-pathogeninteractions(Scherm2003).

eFFecTS oN ecoSySTemS

Becauseindividualspecieswillrespondtoclimatechangedifferently,ecosystemswillnotnecessarilyshiftascohesiveunits.Themostvulnerablespeciesareexpectedtobethosewithnarrowtemperaturetolerances,slowgrowthcharacteristics,andlimitingdispersalmechanismssuchasheavyseeds(LemmenandWarren2004).Howwellplantandanimalspeciesadapttoormovewithchangesintheirpotentialhabitatisstronglyinfluencedbothbytheirdispersalabilitiesandbythecharacteristicsandseverityofdisturbancestotheseenvironments.Nonnativeandinvasivespeciesthatdisperserapidlyarelikelytofindopportunitiesinnewlyformingcommunities(Joyceandothers2001).However,ifclimatechangecausesagradualshiftofcroppingregions,pathogenswillfollowtheirhosts(GoudriaanandZadocks1995)intolesschangednewcommunities.

Thepatternofdisturbanceimposedonalandscapebyaparticularbioticagentisdeterminedbothbythestructureandconditionofthelandscapeandbythecharacteristicsoftheagentanditsresponsivenesstoenvironmentalconditions(MamlstromandRaffa2000).Factorssuchaschangesinlanduseorincreasesinresistantstrainsofdiseasesmayunderlierangeexpansions(Harvellandothers2002).

Daleandothers(2001)pointoutthatmanydisturbancesarecascading.Forexample,insectinfestationsanddiseasespromoteforestfiresbycreatingfuels,andthefiresinturn

promotefutureinfestationsandinfectionsbycompromisingtheresistanceofsurvivingtreestoinsectsanddiseases.Invasivenonnativespeciesaresometimesabletomodifyexistingdisturbancesorintroduceentirelynewones.Underclimatechange,thesecompoundedinteractionsmaybeunprecedentedandunpredictable.Theyarelikelytoappearslowlyandbedifficulttodetectbecauseoftreelongevity.

Climatechangecouldrepresentanewformofdisturbancetounmanagedecosystemsandthuscouldprovidenewopportunitiesforinvasivespeciestoflourishanddisplacenativespecies.Animportantfeatureofmanyinvasivespeciesistheirdispersaleffectivenessandtheirhighreproductiverates(MalcolmandPitelka2000).Changesinphonologicalsynchronicityofhostsandnativepests,aswellastheirrelativeabundanceandphysiologicalcondition,mayaffectthefrequencyandconsequencesofoutbreaks(Malcolmandothers2006).

eFFecTS oN DiSTRiBuTioN oF SPecieS

Asclimateshifts,climaticallysensitivespecieswilleventuallydieout,andonlyasubsetofthepotentialpoolofincomingplantsmayactuallymigratesufficientlyquicklytokeepupwiththeshiftingclimate.Thus,plantcommunitiescouldbecomeprogressivelycomposedofthemoreadaptableandfastermovingspecies,especiallyifwarmingisrapid.Thischangeinplantcommunities,especiallytreecommunities,isofconsiderableconcern.Expansionofthewarm-temperaturemixed-evergreenforestsoftheSouthwouldbeattheexpenseofotherkindsofforests.Insomescenarios,partsoftheSouthbecomedrierandgrasslandsorsavannahsreplacethecurrentforest(MalcolmandPitelka2000).

TheforestareaimpactedbyinsectsanddiseasesintheUnitedStatesisapproximately45timesthatimpactedbyfire,withaneconomicimpactthatisalmost5timeslarger(Daleandothers2001).Ifthistrendcontinues,pestsanddiseasesarelikelytobetheprimarycauseofspecieschangeineasternforestsoverthenextfewdecades.Forecastingthetrajectoryofthosechangesisnearlyimpossiblebecausewecannotpredictwithanycertaintywhichpestsordiseaseswillbeestablished(Lovettandothers2006).Giventhecomplexitiesofclimatechange,andbioticresponsestoit,predictionofthefutureimpactofclimatechangeonemerginginfectiousdiseasesisdifficultexceptonabroadscale.Climatechangecanleadtotheemergenceofpreexistingpathogensasmajordiseaseagentsorcanprovidetheclimaticconditionsrequiredfornonnativediseasestoflourish(Andersonandothers2004).Becauseclimatechangewillallowplantsanddiseasestosurviveoutsidetheirhistoricranges,Harvellandothers(2002)haveprojectedanincreaseinthenumberofinvasivediseases.


The following discussion and analysis is excerpted with only very minor changes from Régnière and Bentz (2008) and provides an example for consideration of a pest present and destructive in the western United States which and its potential impact in the East and South under the influence of climate change.

The mountain pine beetle (Dendroctonus ponderosae) is a native insect of pine forests in Western North America. Although it has a broad geographical distribution, it has been historically confined in the United States, by the distribution of its pine hosts, and in the northern half of British Columbia, by the geoclimatic barrier of the Rocky Mountains. Since the early to mid-1990s, an outbreak has reached unprecedented levels in terms of acreage and number of pine trees attacked. Lodgepole pine (Pinus contorta) is being killed throughout its range, most notably in Colorado and British Columbia. The beetle is also causing very high mortality among whitebark pine (Pinus albicaulis) and limber pine (Pinus flexilis) at high elevations. Historical records from the past century suggest that these ecosystems have had pulses of infestation and mortality but not at the levels currently being observed. Since 2006, the range of infestation has expanded into the Peace River area of north-central Alberta. Climate change may well be involved in this recent northeastward and upward range expansion. Evidence of similar shifts in insect distributions is ample and mounting throughout the world, much of it convincingly linked to climate change.

The primary concern at this time is the likelihood that the infestation will continue spreading eastward into the pines of the Canadian boreal forest, eventually reaching the eastern provinces and threatening the pines growing on the Atlantic side of the continent and then spreading into the Southern United States. Because of its recent incursion to the edges of the Canadian boreal forest, mountain pine beetle is viewed as a potential invading species in eastern pine ecosystems.

Three well-understood links connect climate and mountain pine beetles and form the basis for the concern that changing climate (temperature and precipitation) has had—and will continue to have—a role in the recent outbreaks and range expansion of this insect.

1. A well-synchronized adult emergence pattern is a prerequisite for successful mass attack of healthy pine trees. Such highly synchronized emergence is most likely to occur where (and when) the insect has a strictly univoltine (one generation per year) life cycle.

2. Cold winter temperature is the major cause of mortality in mountain pine beetles. For more than 20 years, process-based models describing responses to temperature have been under development; they show that a hemivoltine life cycle (one generation every 2 years) entails exposure to two winters, leading to lower population performance.

3. Drought affects the ability of pine trees to defend themselves against insect attack.

Three model components are available to study the impact of weather on mountain pine beetle populations: a phenology model that predicts life stage-specific developmental timing, a cold-tolerance model that predicts probability of larval mortality resulting from cold temperature, and a drought-stress model that predicts fluctuations of tree susceptibility. All three models have been implemented within BioSIM to make landscape-scale predictions of mountain pine beetle performance under climate change scenarios. BioSIM is a generic modelling tool that uses available knowledge about the responses of particular species (usually pests) to key climatic factors to predict their potential geographic range and performance.

The phenology model is very good at predicting the portions of the continent where the insect has a high likelihood of being univoltine. This model predicts the northward and upward shift of infestation. Under a conservative climate change scenario, it also predicts that by the end of the 21st century, the area at risk will shift considerably northward, to a point that the insect may be maladapted over much of its current distributional range. The cold tolerance model suggests that winter survival is very low and will remain so in the foreseeable future throughout the boreal pine forests from Alberta to Ontario. Although drought stress is, and is predicted to be, more common in that same area, there is not a very large change in this risk factor predicted in the near future.

Thus, with our current understanding of the insect’s physiology and host plant interactions, the risk of seeing the mountain pine beetle spread across the northern forests of Canada into the eastern pine forests seems rather low. This prediction, of course, is contingent on failure of the insect to adapt (evolve) and change its thermal responses, and on a relatively stable distribution of pines over the time range under consideration.


Describingsimilareffectsforpestinsectsinclimatechangescenarios,Loganandothers(2003)indicatethatthereisahistorictrendtointensificationinallaspectsofoutbreakbehavior,basedonassessmentsofindividualspecies’responsestodate;thiscertainlycharacterizesmodelingworkwiththemountainpinebeetle(Dendroctonusponderosae),gypsymoth,sprucebeetle(Dendroctonusrufipennis),andsprucebudworm(Choristoneurafumiferana).

Waltherandothers(2002)linkclimatechangetochangesinavarietyofknownspringtimelife-cycleeventsinEuropeanorganisms(includingearlierannualbirdbreeding,migrantbirdarrival,theappearanceofbutterflies,chorusesandspawningofamphibians,andshootgrowthandfloweringofplants);thesechangesineventtimingsuggestalengtheningofgrowingseasonby8to16days.Andersonandothers(2004),citinggreyleafspot(Pyriculariagrisea)diseaseofcorn(Zeaspp.),suggestthattherangesofseveralimportantcropinsects,nonnativeplants,andplantdiseaseshavealreadyexpandednorthward.Theyalsonotethatautumnlife-cycleevents(leafcolorchangeandleaffall)arenotasclearlydefinedintheirresponsetotheextensionofgrowingseasonasspringtimeevents.

Plantshavehistoricallyrespondedtoclimatechangebymigrationandadaptation.Fragmentationandrateofseedlingestablishmentmayhindersomeplantpopulationsfromsuccessfulmigrationtohigherlatitudes.Persistenceofthesepopulationsmaydependheavilyonadaptiveevolution,butpredictedratesofevolutionaryresponsearemuchslowerthanthepredictedrateofclimatechange.Historicalclimatechangesweregenerallymuchslower(byoneormoreordersofmagnitude)thanthosepredictedforthefuture(EttersonandShaw2001).Thisobservationleadstoconcernthathistoricalresponsepatternstoclimatechangemaynotprovetobeeffectiveaspredictorsoffuturechange.

Addingtotheconcernsexpressedaboveisacriticalconsiderationthathasnotyetbeenemphasizedenough—climatechangecannotbeviewedinisolation;itseffectsonecosystemsmustbeconsideredinthecontextofarangeofhuman-causedimpactsonecosystems,suchasairpollution,waterpollution,habitatdestructionandfragmentation,andthenonnativespeciesthatthriveandhavetheirmostseriouseffectsinecosystemsalreadydisturbedbyhumanactivities(MalcolmandPitelka2000).

Manyunpredictable,unforeseenpestproblemsmayariseasaresultofchangingtemperatures,changingprecipitationregimes,orbothincombination.Previouslyminororinfrequentpestsmaybecomesignificantcausesoftreemortality.Somecurrentmajorpestsmaydeclineinimportance.Inadditiontonewnonnativeinvasivepestsarrivingfromoverseas,therangesofinsectsanddiseasesnativetoNorthAmericamayexpandor

contractdramatically.Becausethesechangesarelargelyunpredictableyetboundtooccur,landmanagersandscientistsinforestry-relateddisciplineswillneedtopracticeearlydetectionandmonitoringof“new”problemsandfollowupwithresearchandcreative,adaptivemanagementstrategies.

PAThoSySTemS

Thesubtlechangesinconditionsattributedtoclimatechangecanaffectplant-diseasedevelopment.Thesechangesarenoteasilydetermined,and,consequently,theabilitytoforecasthowdiseasechangesunderalteredgrowthconditionsisnotsimple(Seem2004).

Lessstablerelationshipstendtooccurinthesimplerecosystemsthatinitiallyexistinplantedforests,ofteninvolvingnewcombinationsofhostandpathogenspeciesthathavebeentransportedbeyondtheirnaturalgeographicranges.Insuchsituations,climatechangewouldlikelyencouragemajorchangesindiseaseincidenceandseverity(LonsdaleandGibbs1994).

Tree-diseaseproblemscannotbefullyunderstoodwithoutathoroughappreciationofthepartplayedbyenvironmentalfactors,particularlyclimate,asaprecursortofungalattack.Themanifestationofmanydiseasesoftenmerelyreflectsunfavorablesitefactors,thepresenceofthefungusbeingtheresultofanunhealthyconditionratherthantheprimarycauseofthetree’sdebility(Gilmour1960).

Duringunusualweathereventsorbiologicallyinducedstressperiods,thecompetitivedominantmaybethemostvulnerable.Itslargesizehasstretcheditslimitstocoordinateuptake,transport,storage,andphotosynthesis(ManionandLachance1992).

Thetimingofthestresseventisalsoveryimportant.Earlyseasonstressisfrequentlyovercomealthoughlaterstressorsarenotso,oftensimplybecauseofsufficienttimeremaininginthegrowingseason(LundquistandHamelin2005).

NonnativeinsectpestsanddiseasesposethemostseriousthreattotheforestsofeasternNorthAmerica.Thelitanyofpestanddiseaseintroductionsislong:chestnutblight(Cryphonectriaparasitica),Dutchelmdisease(Ophiostomaulmi),beechbarkdisease(Nectriacoccineavar.faginata),balsamwoollyadelgid(Adelgespiceae),hemlockwoollyadelgid(A.tsugae),dogwoodanthracnose(Disculadestructiva),andgypsymoth(Lovettandothers2006).

AccordingtoLovettandothers(2006),ecologistsneedadequateinformationinonlysixcategoriesofknowledgeaboutnonnativepestsandtheirhoststomakeroughpredictionsofthetypeandmagnitudeofpotentialecosystem


impacts.Pestinformationisneededconcerning:(1)modeofaction,(2)hostspecificity—suchasspeciesandageclass,and(3)virulence.Withrespecttothehost,theinformationneededis:(4)ecologicalimportance—positionorbio-productionvaluesinthesystem,(5)uniqueness,and(6)phytosociology—suchaspureversusmixedstands,effectivenessofregeneration.

Whenclimatechangehasasignificantanddirecteffectonplants,changesincompositionmayensue.Givendifferentialresponsesacrossplantspecies,thismayleadtorelativechangesincommunitycomposition.Whencoupledwithrangeextensionsorcontractionsofindividualspecies,theresultmaybeincreasedordecreaseddiversityofwholeplantcommunities.Diseasesofonehostspeciesmaythusbebroughtintointimatecontactwithnewhosts,althoughthelikelihoodofspatialmovementsnecessaryforthistooccurisperhapslowintheimmediatefuture;theymaybenefitfromincreasingoverlapofobligatealternatehostdistributions;ortheymaysuffersignificantreductionsinpopulationsizeasaconsequenceofallopatricdistributionsorincompletecongruenceinthedistributionofobligatealternatehosts(Burdonandothers2006).

Bolandandothers(2004)summarizeresearchonthepotentialimpactofclimatechangeonplantdiseasesandlist143plantdiseases,only18ofwhichareforesttreediseases.Despitethistheytabulatedataforclimatechangeeffectswithrespecttoforestpathosystemsunderthesecategories:primaryinoculumordiseaseestablishment,rateofdiseaseprogress,potentialdurationofepidemic,reasonsforeffects,andneteffectofthedisease.Althoughpredictingtheeffectsonthediseasesisrelativelyintuitivetoplantpathologists,theauthorsarguethatextendingtheintuitiveknowledgepathosystemsordiseasemechanismsrequiresmoreknowledgeabouthowthehost’sphysiologyandthusthehost-pathogeninteractionwillbeaffected.Theyalsociteaspecificneedforfurtherknowledgeabouttheeffectsofelevatedcarbondioxide,UVradiation,andgroundlevelozone,aswellastheeffectsofenvironmentalchangesoninsectvectorsofdiseases.

Aninterestingsidebartopathosystemsactivityisreflectedinthecapacityoffungitoperformtheircleanupfunction(woodyandleaflitterdecomposition)undertheinfluenceofclimatechange.Yin(1999)makesseveralpoints.First,thedecayrateofforestwoodydebrisisakeymissinglinkinourquantitativeunderstandingofcarbondynamicsandtheglobalcarbonbudgetofforests.And,inthecontextofglobalclimatechange,a2°CwarminginairtemperatureinJanuaryandJulywouldacceleratestemwoodydebrisdecay(indensityloss);accelerateddecaywoulddecreaseinthepresenceofincreasedprecipitation(andvice-versa);but,themagnitudeofincreasewouldbesmallerwhenadjustedforthedetrimentaleffectofelevatedcarbondioxideaspartofclimatechange.

Formanyfungaldiseasesthatrelyonbioticvectorsfordispersal,theeffectsofclimatechangeandweatheronthedevelopmentofoutbreaksorepidemicshavenotbeenstudiedindetail.Inareaswhereapathogenalreadyoccurs,weatherconditionsmayfavoroutbreaksofitsvectorsincertainyears,suggestingthatclimatechangecouldinfluencelong-termprevalenceofthedisease(LonsdaleandGibbs1994).Theintroductionofnewvectorspecies,changesinvectoroverwinteringandoversummering(Garrettandothers2006),andothereffectsofchangeoninsectsmayhaveimportanteffectsonpathogensurvival,movement,andreproduction(Garrettandothers2006).Pathogensthatrelyonvectorsmayseesignificantshiftsintheirdistributionorintensityifenvironmentalchangesaffectthebehaviororviabilityoftheirvector(Burdonandothers2006).

However,insomecircumstances,warmertemperaturescouldactuallyinhibitinsectactivityordisruptthebuild-upofpopulations.Enemiesofinsectpestswillalsobeaffectedbyclimatechange,buttheseeffectsareunknownandrequiremoreresearch.Ifwarmertemperaturespositivelyaffectpredatorsandparasitoids,naturalenemieswillexhibitgreatercontrolofpestspecies.Conversely,ifwarmertemperaturesdisruptordecreasepredatorandparasitoidpopulations,pestpopulationswillgrowmorequicklyandwillpersistathigherlevelsforlongerperiods.

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oTheR ReFeReNceS

Annosum Root Disease

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Asian longhorned Beetle

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Baldcypress leafroller

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Balsam Woolly Adelgid

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Brown Spot Needle Blight

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emerald Ash Borer

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Forest Tent caterpillar

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Fusiform Rust

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Gypsy moth

Elkinton,J.S.;Liebhold,A.M.1990.PopulationdynamicsofgypsymothinNorthAmerica.AnnualReviewofEntomology.35:571–596.

Gottschalk,K.1993.Silviculturalguidelinesforforeststandsthreatenedbythegypsymoth.Gen.Tech.Rep.GTRNE-171.Radnor,PA:U.S.DepartmentofAgricultureForestService,NortheasternForestExperimentStation.49p.

McManus,M.;Schneeberger,N.;Reardon,R.;Mason,G.1989.Gypsymoth.ForestInsect&DiseaseLeaflet162.Washington,DC:U.S.DepartmentofAgricultureForestService.14p.(availableathttp://www.fs.fed.us/r6/nr/fid/fidls/fidl-162.pdf).

U.S.DepartmentofAgriculture,ForestServiceandAnimalandPlantHealthInspectionService(USDAFSandothers).1995.GypsymothmanagementintheUnitedStates:acooperativeapproach.[UnnumberedRep.].Washington,DC:U.S.DepartmentofAgricultureForestService.Various[total1092p.]

hardwood Borer

Donley,D.E.;Accivatti,R.E.1980.Redoakborer.ForestInsect&DiseaseLeaflet163.Portland,OR:U.S.DepartmentofAgricultureForestService.7p.(availableathttp://www.fs.fed.us/r6/nr/fid/fidls/fidl-163.pdf).

Graham,S.A.1959.Controlofinsectsthroughsilviculturalpractices.JournalofForestry.57:281–283.

Hay,C.J.;Morris,R.C.1970.Carpenterworm.ForestPestLeaflet64.Washington,DC:U.S.DepartmentofAgricultureForestService.8p.(availableathttp://www.fs.fed.us/r6/nr/fid/fidls/fidl-64.pdf).

hemlock Woolly Adelgid

U.S.DepartmentofAgriculture,ForestService(USDAFS).2005.Hemlockwoollyadelgid.PestAlertNA-PR-09-05.NewtownSquare,PA:U.S.DepartmentofAgricultureForestService,NorhteasternArea,State&PrivateForestry.2p.(Also::http://na.fs.fed.us/spfo/pubs/pest_al/hemlock/hwa05.htm).

U.S.DepartmentofAgriculture,ForestService(USDAFS).2010.Hemlockwoollyadelgid[homepage].NewtownSquare,PA:U.S.DepartmentofAgricultureForestService,NortheasternArea.Variousp.[http://na.fs.fed.us/fhp/hwa/].

littleleaf Disease

Anderson,R.L.;Mistretta,P.A.1982.Managementstrategiesforreducinglossescausedbyfusiformrust,annosusrootrot,andlittleleafdisease.Agric.Handbk.597.Washington,DC:U.S.DepartmentofAgricultureForestService.30p.


Mistretta,P.1984.Littleleafdisease.ForestInsect&DiseaseLeaflet20.Washington,DC:U.S.DepartmentofAgricultureForestService.6p.(availableathttp://www.fs.fed.us/r6/nr/fid/fidls/fidl-20.pdf).

Nantucket Pine Tip moth

Berisford,C.W.1974.Comparisonsofadultemergenceperiodsandgenerationsofthepinetipmoths,RhyacioniafrustranaandR.rigidana.AnnalsoftheEntomologicalSocietyofAmerica.67:666–668.

Berisford,C.W.;Kulman,H.M.1967.InfestationrateanddamagebytheNantucketpinetipmothinsixloblollypinestandcategories.ForestScience.13:428–438.

Eikenbary,R.D.;Fox,R.C.1965.TheparasitesoftheNantucketpinetipmothinSouthCarolina.Tech.Bull.1017.Clemson,SC:SouthCarolinaAgriculturalExperimentStation.9p.

Eikenbary,R.D.;Fox,R.C.1968.ArthropodpredatorsoftheNantucketpinetipmothRhyacioniafrustrana.AnnalsoftheEntomologicalSocietyofAmerica.61:1218–1221.

Fettig,C.J.;Berisford,C.W.1999.NantucketpinetipmothphenologyineasternNorthCarolinaandVirginia:implicationsforeffectivetimingofinsecticideapplication.SouthernJournalofAppliedForestry.23:30–38.

Nowak,J.T.;Berisford,C.W.2000.Effectsofintensivemanagementpracticesoninsectinfestationlevelsandloblollypinegrowth.JournalofEconomicEntomology.93:336–341.

Warren,L.O.1985.PrimaryhymenopteransparasitesofNantucketpinetipmoth,Rhyacioniafrustrana(Comstock).JournalofEntomologicalScience.20:383–389.

Yates,H.O.,III;Overgard,N.A.;Koerber,T.W.1981.Nantucketpinetipmoth.ForestInsect&DiseaseLeaflet70.Washington,DC:U.S.DepartmentofAgricultureForestService.8p.(availableathttp://www.fs.fed.us/r6/nr/fid/fidls/fidl-70.pdf).

oak Decline

Oak,S.W.;Courter,A.2000.Modelingoakdeclineeffectsonforestcompositionandstructurechangeusingtheforestvegetationsimulator[Abstract].In:Anon.Proceedingsofthefirstjointmeetingofthenortheastandsouthwideforestdiseaseworkshops.Morgantown,WV:WestVirginiaUniversity.[Notpaged].

Oak,S.W.;Huber,C.M.;Sheffield,R.M.1991.IncidenceandimpactofoakdeclineinwesternVirginia1986.Resour.Bull.SE–123.Asheville,NC:U.S.DepartmentofAgricultureForestService,SoutheasternForestExperimentStation.16p.

Oak,S.;Tainter,F.;Williams,J.;Starkey,D.1996.OakdeclineriskratingfortheSoutheasternUnitedStates.AnnalsdesSciencesForestiere.53:721–730.

oak Wilt

Appel,D.N.;Billings,R.F.,eds.1995.Oakwiltperspectives:Proceedingsofthenationaloakwiltsymposium.CollegeStation,TX:TexasForestService,TexasAgriculturalExperimentStation,TexasAgriculturalExtensionService.217p.

Pine Reproduction Weevil

Corneil,J.A.;Wilson,L.F.1980.Palesweevil—rationaleforitsinjuryandcontrol.MichiganChristmasTreeJournal.Fall:16–17.

Grosman,D.M.;Billings,R.F.;McCook,F.A.;Upton,W.W.1999.Influenceofharvestdateandsilviculturalpracticesontheabundanceandimpactofpinereproductionweevilsinwesterngulfpineplantations.In:Haywood,James,D.,ed.Proceedingsofthetenthbiennialsouthernsilviculturalresearchconference.Gen.Tech.Rep.SRS–30.Asheville,NC:U.S.DepartmentofAgricultureForestService,SouthernResearchStation:565–568.

Speers,C.F.1974.Palesandpitch-eatingweevils:developmentinrelationtotimepinesarecutintheSoutheast.Res.NoteSE–207.Asheville,NC:U.S.DepartmentofAgricultureForestService,SoutheasternForestExperimentStation.7p.

Stevens,R.E.1971.Pinereproductionweevil.ForestPestLeaflet15.Washington,DC:U.S.DepartmentofAgricultureForestService.6p.(availableathttp://www.fs.fed.us/r6/nr/fid/fidls/fidl-15.pdf).

Southern Pine Beetle

Clarke,S.R.;Nowak,J.T.2009.Southernpinebeetle.ForestInsect&DiseaseLeaflet49.Portland,OR:U.S.DepartmentofAgricultureForestService.8p.(availableathttp://www.fs.fed.us/r6/nr/fid/fidls/fidl-49.pdf).

Price,T.S.;Doggett,C.;Pye,J.M.;Smith,B.1998.AhistoryofsouthernpinebeetleoutbreaksintheSoutheasternUnitedStatesbythesoutheasternforestinsectworkinggroup.Macon,GA:GeorgiaForestryCommission.72p.

Swain,K.M.;Remion,M.C.1981.Directcontrolofthesouthernpinebeetle.Agric.Handbk.575.Washington,DC:U.S.DepartmentofAgriculture.15p.

Texas leaf cutting Ant

Bennett,W.H.1958.TheTexasleaf-cuttingant.ForestPestLeaflet23.Washington,DC:U.S.DepartmentofAgricultureForestService.4p.(availableathttp://www.fs.fed.us/r6/nr/fid/fidls/fidl-23.pdf).

[Grosman,D.]n.d.Leaf-cuttingant.Webpage.CollegeStation,TX:TexasForestService.(Availableat:http://txforestservice.tamu.edu/main/popup.aspx?id=1187(Accessed:Jun.28,2010.)

Cherret,J.M.1986.Historyoftheleaf-cuttingantproblem.In:Lofgren,C.S.;VanderMeer,R.K.,eds.Fireantsandleaf-cutting-antsbiologyandmanagement.Boulder,CO:WestviewPress:10–17.

Chapter 16. invasive Pests—insects and Diseases

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