Managing Forests for Wildlife - Southern ResearchSome species, such as white-tailed deer and northern cardinals, are tolerant of a wide range of habitat condi-tions Conversely, other

Managing Forestsfor Wildlife

James G. Dickson’US Forest Service

Southern Research Station, Nacogdodws, TX

T. Bently WigleyNdond Council of the Paper Industry Jar Air und

Stream Improvement, Inc.Clemson University, Clemson, SC

wood ducks that winterextensively in southern bot-toms, nest throughout muchof forested North America.

And probably moreimportantly than use by indi-vidual animals, broad-scalelandscape habitat conditionsaffect wildlife communitycomposition and populationfunction of species. Forexample, very small pocketsof forest habitat may serveas sinks for forest interiorbirds, where mortalityexceeds productivity.

In this chapter we pres-ent some information about

habitat relationships and management options at a scalebroader than the stand level, such as discussion of edgeand streamside zones. But we treat wildlife habitat rela-tionships primarily at the stand level, which is the basicmanagement unit. We approach this by treating suitabil-ity of stand structure and composition for wildlife com-

Wildlife species and commu-nities are molded and inf-lu-enced by a variety of factors,including some abiotic con-ditions such as climate,topography, soils, and site.These conditions form thebasis for productive anddiverse southern forests andtheir wildlife communities.

These wildlife communi-ties are affected by habitatconditions at different scales,such as the landscape leveland the smaller, stand scale.Species are very different inthe scale of habitat that indi-vidual animals use. Forexample. some amphibians have very restricted move-ments and ranges. Conversely, some larger vertebratessuch as white-tailed deer have relatively large homeranges.

Some migratory species may use very distant anddifferent habitats at different seasons. For example.

x3

C .

Wide streamslde zones (A. US Forest SewIce) in southern forestsare heneflciai for a number of game (S. R. Gnffm) and nongamespecies such as the Acadian flycatcher (C. 8. Cottn//e, Cornell Labof Ormthology).

MANAGING F O R E S T S F O R W I L D L I F E 85

munities, and present information about how commonmanagement practices affect that suitability as wildlifehabitat for wildlife communities. Each species has dif-ferent habitat requirements, SO conditions or manipula-tions that favor some species likely will be negative forothers.

Forest and stand suitability for wildlife should beconsidered in regard to alternative land uses and alsohow they fit into the broader landscape context. Inrecent years pine plantations have increased in extent inthe South, there is much interest in pine plantations aswildlife habitat, and much of this chapter focuses onthose relationships.

EDGE

As noted, landscape composition is important to south-ern wildlife communities. One factor which influenceswildlife species is edge, or the juxtaposition of habitattypes. The extent of edge is often determined by standsize or shape. Small stands or complex-shaped standshave large edge to area ratios. Edge has long been rec-ognized as positive for many species (Leopold 1933).Most primary game species in the South thrive in forestedge habitat and in forest-field landscapes. For exam-ple, white-tailed deer and wild turkey thrive in forest-agriculture habitat mixes which are prime habitat fortheir year-round needs. Also, some other game birds,such as American woodcock and ruffed grouse, andsome other species fare well in patchy habitat.

But there is concern for some forest interior birds,particularly neotropical migrants (Dickson et al. 1993).These species may be absent from small forest frag-ments, probably due to lower reproductive success orsurvival in edge-dominated forests (Faaborg 1992).While edge-related declines in reproductive successhave been documented in fragmented forests in pre-dominantly agriculture landscapes, the effects of edgescreated by timber harvest in predominately forestedlandscapes is unclear (Dickson et al. 1993). Many for-est interior species remain abundant in managed forestsbut the status of their population viability is uncertain.

STREAMSIDE ZQNES

Streamside zones (SZ) are strips of riparian and/or othermature stands maintained along intermittent or perma-nent streams (Wigley and Melchiors 1994). SZ usuallyare recommended in silvicultural Best ManagementPractices to protect streams from potential impacts fromlogging of adjacent stands, such as excessive sediment,

nutrients, logging debris, chemicals, or water tempera-ture alteration.

SZ also help maintain wildlife diversity in managedforest landscapes. Because riparian forests often pre-dominate in SZ, they are very productive and often pro-vide unique habitat in landscapes dominated by morexeric forest types. SZ also may provide importantmature habitat attributes and may function as travel cor-ridors and enhance connectivity within landscapes(Burk et al. 1990). SZ research in the South has docu-mented habitat relationships for nongame birds, smallmammals, herpetofauna, wild turkey, squirrels, andwhite-tailed deer.

BirdsSome habitat features that SZ offer birds include largetrees and snags, multiple foliage layers, and open areasto forage along the land/water interface. Bird speciespresent in SZ depend upon habitat conditions of the SZand adjacent habitats. Thus SZ may s>lpport forest-inte-rior species, riparian associates, early-successionalspecies, and generalists (Murray and Stauffer 1995).

SZ width is a major consideration for many forestmanagers. Bird species richness usually increases withSZ or riparian zone width (Dickson et al. 1995a,Hodges and Krementz 1996). Different bird species,however, respond differently to increasing width. Forexample, Keller et al. (1993) found that the number ofneotropical migrants increased with riparian forestwidth, but the number of short-distance migrantsdecreased. and resident species were not affected.Forest-dwelling and forest-interior species have beenfound to be more common in wider strips (Dickson et al.1995a). However, data on reproductive success of forestinterior species are lacking in these narrow habitats.

Game SpeciesSZ also can be important habitats for game species. Ineastern Texas, Poteet et al. (1996) found that SZ travers-ing pine plantations were heavily used and an importantpart of deer home ranges during fall and winter. proba-bly due to hard mast availability. Telemetry data showthat SZ are heavily used by eastern wild turkeys, alsoprimarily during fall and winter iBurk et al. 1990).Streamside zones at least 50 yards in total width appearto be necessary to provide adequate habitat for gray andfox squirrels (Dickson and Huntley 1987).

Small MammalsMicrohabitat features within SZ such as dense vegeta-tion. fruits. seeds. down logs. and logging slash are

86 MANAGING FORESTS FOR WILDLIFE

important to small mammals (Dickson and Williamson1988). Wider SZ may support small mammal commu-nities associated with mature forests (Thurmond andMiller 1994). However, other studies have shown thatcharacteristics of small mammal communities such asrichness, diversity, and abundance can be similar acrossdifferent SZ width-classes, or even higher in narrowstrips (Dickson and Williamson 1988). Therefore, forsmall mammal communities, microhabitat featuresprobably are more important than SZ width.

HerpetofhunaObviously, SZ offer important habitat features for her-petofauna, such as pools of water, moist soils, downwood, and Ieaf litter. However, there are few data onthese relationships, and results appear to vary. In easternTexas, Rudolph and Dickson (1990) found the fewestamphibians and reptiles in narrow (less than 25 yardswide) strips and concluded that abundance of herpeto-fauna was positively related to closed-canopy condi-tions. But in Kentucky, Pais et al. (1988) found that her-petofaunal species richness was greatest in open,wildlife clearings while mature forest supported thefewest species. They concluded that herpetofauna rich-ness was most affected by biomass of nonwoody vege-tation and proximity to water.

ManagementRetention of SZ in southern forests is positive forwildlife communities. Generally, streamside zoneswider than about 50 yards total width appear beneficialfor forest interior species, several important gamespecies, and other species. Specific requirements ofsome species remain unknown.

Extent and management of SZ should be consideredin the context of economics and adjacent land use, aswell as site-specific factors, such as topography, adja-cent habitats, and stream width. Management of SZ,including silvicultural operations, could enhance habitatsuitability for many wildlife species. For example, hardmast-producing oaks, soft mast-producing shrubs. orcavity trees could be featured. Or species regarded aspests, such as Chinese tallow tree, could be controlled.

STAND STRUCTURE ANDCOMPOSITION

Within-stand structure and composition are importantfactors in habitat suitability for many species. Structuralfeatures. such as stand overstory, understory, leaf litter.snags, and down wood, may be important to different

Structure is important in determining habitat suitability of foreststands. This open stand is suitable for species associated withstand canopy as well as those associated with understory (US Fish& Wildlife Serwce).

MANAGING FORESTS FOR WILDLIFE 87

Oak mast is an important food for a number of species, such as white-tailed deer, wild turkey, black bear, chipmunk and gray squirrel. But acornproduction is quite variable from year to year (H. Williamson, US Forest Service).

range from several hundred pounds per acre to almostnone in other years (Rogers et al. 1990). The white-oakgroup produces acorns in 1 growing season and redoaks in 2 growing seasons. Therefore, a variety of oaksand other hardwood species such as black ,oum providediverse habitat and foods. But hardwood overstoriesand midstories intercept much sunlight, shading shrubsand limiting fruit production. Also, hardwood shadinglimits herbaceous ground vegetation (Blair andFeduccia 1977) and associated species.

HARVEST AND REGENERATION

Stand or tree harvesting can be a drastic habitat alter-ation (see Chapter 4, Defining the Forest). For example,bird species associated with forest canopy generallydecreased and birds associated with patchy and earlysuccessional habitat increased following harvest (Webbet al. 1977). Of course, response of vegetation to har-vesting depends on extent of tree. particularly oversto-ry, removal. The more overstory removed the more pro-found the vegetative response. change in habitat suit-ability for wildlife. and change in wildlife communitycomposition (Dickson 198 1). Single-tree selection har-vesting affects stands and wildlife communities theleast during each harvest. With this technique. standstructure remains mostly intact. However, uneven-agedmanagement of southern pines requires more frequent

harvest cycles and hardwood control. Clearcuttingalters habitat and wildlife communities the most. Withcomplete tree removal, forage and fruiting near theground is increased many fold over that in shadedunderstories (Halls and Alcaniz 1968, Blair andEnghardt 1976). Group selection, shelterwood and seedtree cuts are intermediate in effects on habitat andwildlife communities, depending on the extent of standremoval.

SITE PREPARATION

Site preparation includes measures conducted shortlybefore or after stand regeneration to reduce vegetationcompeting with pines. Moderate site treatment meas-ures that delay development or modify non-pine vege-tation can enhance vegetation diversity and wildlifehabitat, particularly for early-successional species(White et al. 1975). For example, in East Texas after 3growing seasons fruit production was lower on KG-bladed and chopped plots than on control or burnedplots (Stransky and Halls 1980). But measures thatseverely reduce vegetation may be negative for manyspecies of wildlife. Generally, the reduction of hard-woods in young stands favors herbaceous vegetationand species associated with that habitat type and disfa-vors the Inany species associated with the hardwoodcomponent of pine stands.

88 MANAGING FORESTS FOR WILDLIFE

STAND DEVELOPMENT

Some species, such as white-tailed deer and northerncardinals, are tolerant of a wide range of habitat condi-tions Conversely, other species have more specifichabitat requirements, and respond to changes in standstructure and composition as stands age (Buckner andLanders 1980, Dickson 1981). During the first year ortwo of development, stands usually are dominated bygrass-forb vegetation. At this stage young pine standsare suitable habitat for some bird species, such asmourning doves (Lay and Taylor 1943), eastern mead-owlarks (Johnston and Odum 1956) and prairie war-blers (Dickson et al. 1995). Grass-forb vegetation alsoprovides suitable brood habitat for newly-hatchedchicks of primary game birds: northern bobwhites, wildturkeys and ruffed grouse, which depend on and feedextensively on arthropods. Also, populations of herbiv-orous and granivorous small mammals, such as cottonrats and Peromyscus spp., thrive in early successionalhabitat (Atkeson and Johnson 1979).

Normally within a couple of years, rapidly growingvegetation invades young stands. Timing and character-istics of this vegetation depend on site quality, priorland use, and source of revegetation, as well as herbi-cide and other site preparation treatments. In the South,young pine stands less than about 8 years old normallyare characterized by diverse, lush herbaceous andwoody vegetation. Forage production often exceeds2,000 lbs per acre (Harlow et al. 1980), and fruit (softmast) is abundant. For example, in eastern Texas Halls

U s u a l l y t h e r e i s a n abunciancc ancl varict\/ o f

wilcllit’~ i n youn g brushy stands. White-tailc~l deer- t’:~rewell in this habitat with ~tbundant browse :111tl sol’t least

(Blymyer ;ml Mosby 1977). In this dense hal>irat LISLI~II-ly there is an ~kbunciar~ce 01- herbivorous sriIall i11~~iii1n;~ls(Umber and Harris 197-i. Atkson a11cl JO~IIKOI~ 1970).Also, there xe abundant birds (Co~tner. and Aclkisson1975. Dickson et 4. I c)% 1: typical heeding masonspecies include field spam~ws. yellow-breasted chats,w h i t e - e y e d vireos, prairie wxblers. ~111cl p;Gntecl andindigo buntings (Johnston and Oclum 1956. Dicksonand Segelquist 1979, Dickson et al. I995).

Usually there is an abundance and varietyof wildlife in young brushy stands (A. J.D u n n i n g , C o r n e l l L a b o f O r n i t h o l o g y ) .Forage and soft mast production usually ishigh in these rapidly developing stands(B. US Forest Service C. H. Williamson,).

As stands age and trees grow into the pole stage.suitability for wildlife changes. Some early succession-al species continue to use openings which have consid-erable hardwood or grass-forb vegetation. And somespecies associated with mature stands. such as yellow-billed cuckoos and red-eyed vireos in the canopies andhooded warblers in the understories. begin to inhabitstands with hardwood vegetation. In pine plantationsabout 7 to 10 years old or similar hardwood stands.pole-sized trees dominate the stand. canopies close. andshading by canopies drastically reduces ve:rtationbeneath the canopies and I‘ruit production of shrubs(Halls and Aicanit I%#). Generally, habital suilabiliryfor Lvildlife is reduced substantially. Usually there is lit-tle low vegetation . and bird iDickson and Segelqixl1979) a n d s m a l l ~na~~~~nal Imp~llationx (Akx~n XKIJohnson I979) decline. and habitat suitabiliry I’OI- deerand wild turkcvs dinlinihhes rr.2.. Miller et 31. IC)V)).

THINNING

Young, dense, closed-canopy stands have little value for wildlife(H. Williamson).

trees are removed to concentrate tree growth on theremaining crop trees. Tree removal opens up canopiesand allows light into the understory. This promotes non-pine vepetation growth and fruiting, which is positivefor many species.

As even-aged stands mature. some trees die andsmall openings develop. creatin g structural diversity.Also maturing trees produce mast. importnnt to a num-ber 01’ slxcies of wildlife. Generally suitability forwiltllil’e is hi$l in diverse mature stmds. especially(hose with openings. FOI- example. deer inhabit maturesrands as well as stands of other ages. Gray rind ~‘OXsq~~irrels usual ly are ~tbuncl~lnt in mature hardwoodst:lmis. And there are high densities of breeding birds.XIICII ;IS yellow-billed cuckoo. tufted titmouse. red-eyedvireo. and summer ~xiager in mature hardwood stands,ant1 Ilrown-Ileadecl nuthatch. pine warbler. and red-COCI;;KI~CI WOO~I~~CIW in mature pine stands (DicksonCl ,II. I’NS).‘

Logs and woody debris pro-vide important habitat for anumber of species of smallmammals, amphibians, andreptiles, such as the timberrattlesnake, which hibernatesin logs and also waits adjacentto logs for prey (C. Rudolph).

In stands designated for old growth, as standsapproach old-growth condition habitat suitabilitychanges. Tree fall creates openings and enhances standdiversity. Tree decay increases, which provides cavityand foraging substrate for cavity-using wildlife. Anddown material from trees provides structure on theground inhabited by small mammals, and a variety ofamphibians, and reptiles.

SNAGS AND DOWN WOOD

Snags, dead or partially dead trees, are used by andare important to a variety of wildlife species for nest-ing, roosting, foraging, perching, and other uses.Woodpeckers are primary cavity nesters that exca-vate cavities in snags. These cavities are used fornesting and roosting by primary cavity nesters andsecondary cavity nesters, such as great crested fly-catchers, wood ducks, and other species. includingsome mammals (Conner 1978).

Availability of cavities for nesting sites may limitsome populations, and leaving or creating snags 01artificial nest structures may accommodate somespecies. For example, in Arizona the number of cavitynesting birds declined by about half after conifer snagswere removed during timber harvest (Scott 1979). Inyoung pine plantations in the South. bird populationswere increased by creating snags using herbicides(Dickson et al. 1993).

Snags may result from natural phenomena such asinsects, disease, lightning, or other factors; or can becreated through girdling, herbicides, or other means.Dead snags do not compete with crop trees for space,nutrients, moisture. or light. Recommendations forsnag size and density for different species are present-ed by Evans and Conner (1979). But there may besome negative aspects of snags. They may be used asperches to search for prey by brown-headed cowbirdsand raptors. Also, snags may pose a safety hazard forworkers.

Artificial nest structures may accomodate cavity-nesting wildlife in local situations. For example, east-ern bluebirds successfully nested in artificial nestboxes in a young pine plantation (Hurst et al. 1979).But widespread application is prohibitive for all cavity-using species.

Down wood, or woody material on the ground fromdead limbs, snags. or logging debris, is an importantstructural feature. Wood on the forest floor in varyingstages of decay may be instrumental in forest nutrientcycling, supports a wide variety of invertebrates, and isimportant to some species of vertebrates. Logs mayharbor prey for some larger species, such as blackbears. Small mammal populations may be closely asso-ciated with woody material on the forest floor (seeChapter 26. Terrestrial Small Mammals). Species ofsmall mammals, such as Pero~ny~c~t.~ spp. and easternwoodrats. use woody material for protection from prey

i\/l.iN/\(ilN(i 1;Ol<l1\-l’S I-OR ~‘II.L)I.II-.E 91

Ohvioiisly. f ire has the potent ia l to k i l l ;tnimals.However. there is little evidence of significant direct

Prescribed burning has a long history in southern forests. It has been a major technique for the enhancement of wildlife habitat(US Forest Service).

92 MA N A G I N G F O R E S T S F O R W I L D L I F E

mortality of vertebrates from prescribed burning(Landers 1987); and what does occur probably isinsignificant on a landscape scale.

Some animals actually are attracted to the heat andsmoke of fires, or to the burns shortly thereafter.Raptors, such as red-tailed hawks, kestrels, otherhawks, and owls have been observed attracted to burnsin search of prey (Landers 1987). Wild turkeys andmourning doves are attracted to new burns in search ofexposed insects and seed. White-tailed deer are knownto congregate on recent burns and lick the ash, appar-ently to obtain minerals.

Also, although our knowledge of fire effects is lim-ited, arthropod populations and their interactions withvertebrates certainly are affected by fire (Landers 1987).It has been documented that parasites of wild turkey,northern bobwhite, and rabbits are reduced by burning.

Fire is commonly used to manage wildlife habitat inthe South. Generally fire consumes the forest floor litterand sets back succession; usually reducing smaller hard-woods in favor of pines and herbaceous vegetation. Fireeffects are quite variable because they involve conditionof the area before burning and suitability for a wide vari-ety of different communities or species; the intensity,periodicity, and seasonality of fires; landscape contextand unburned areas, and numerous interactions. Forexample, areas burned annually for northern bobwhitesare virtually devoid of hardwood shrubs, whereas areasburned occasionally with cool bums may be thick withhardwood sprouts. We approach this treatment bydescribing how fire may affect different forest stands orplants, and how that may affect different species ofsouthern wildlife. Readers interested in fire effects onparticular species are referred to appropriate chapters.

Prescribed burning normally is used in upland pinestands; mature pines are relatively fire resistant. Sincefire causes wounds in hardwood trees it is not normal-ly used in stands managed for quality hardwood timber.But fire affects hardwoods and their suitability forwildlife. Fire wounds on hardwood trees provideentrance for decay, that over time may become cavitiesused by animals such as tree squirrels. Severe fire maykill trees and create snags that are used by a variety ofcavity-using wildlife. But conversely, dead snags usedby cavity nesters may be consumed by fire. Firessevere enough to kill trees or cause snags to fall andproduce woody debris on the ground would favor avariety of small mammals such as Peromyscus spp.Fires that consume woody debris on the ground, suchas site preparation burns, would decrease area suitabil-ity for small mammals.

Prescribed fire is used for red-cockaded woodpeck-ers to reduce hardwoods and maintain a pine Savannahhabitat. The birds peck cavity trees to produce a resinflow around the cavity and down the tree bole. Fire mayignite the resin up the tree bole of cavity trees and mayeven burn out and gut the nest cavity. So surface fuelaround cavity trees may need to be raked away beforeburning.

Typically, frequent, intense, or growing season firereduces small hardwoods and shrubs. Numbers of smallmammals and rabbits probably are reduced with thecover reduction immediately after a fire. Birds associatedwith shrub-level vegetation and hardwood midstory, suchas northern cardinal, Carolina wren, hooded warbler, andKentucky warbler, probably would be reduced inresponse to shrub hardwood reduction (Dickson 1981).

This shrub-level reduction is accompanied by agrowth flush of herbaceous vegetation which usuallypersists for a few years. This grass-forb growth withabundant seed production favors populations of earlysuccessional breeding bird species, herbivorous andgranivorous small mammals, and provides importantbrood habitat for northern bobwhites, wild turkeys, andr&fed grouse. And the conditions maintained by burningshould favor other species such as the gopher tortoise,which burrows in sunlit sites and forages on herbaceousvegetation resulting from fire (Landers 1987).

There is some evidence that the consumption of fuelcan increase temporarily the nutrient content of post-fire vegetation, such as protein and phosphorus, whichgenerally is limited in the South. This increase in nutri-ent content and palatability of plants could benefit anumber of species, such as deer (Stransky and Harlow1981) and rabbits, whose reproductive success maydepend on forage nutrient quality (Hill 1972).

After a couple of years the post-fire herbaceousvegetation is gradually repiaced by hardwood sproutsand shrubs. This transition affects vertebrate communi-ties as detailed in the stand composition section of thischapter. Also, fruiting of shrubs recovering from fireand those benefitting from reduction of vegetative com-petition from fire increase. This fruit production bene-fits a number of fruit-consuming species, such as white-tailed deer, wild turkey, northern bobwhites, and someomnivorous furbearers, such as coyotes, foxes, opos-sums, and raccoons (Landers 1987).

HERBICIDES

Herbicides are used to control plants that are exotic.noxious, competitors with crop trees, or are otherwise

MANAGING FORESTS FOR WILDLIFE 93

undesirable. Growth of crop trees is enhanced throughthe reduction of competition (Autter and Miller 1998).Herbicides are applied at various times during a rota-tion such as during site preparation or thinning, andoften are effective for vegetation control. For example,mechanical site preparation involves high equipmentcosts and may not be suitable for all landowners orsites. Vegetation control using herbicides is increasing-ly common because of: (I) increased availability ofmore selective and environmentally compatible chemi-cals; (2) rising costs and less available labor for alter-native control methods; and (3) other considerations,such as liability, effects on productivity, and limitednumber of suitable days for burning (Miller and Witt1991).

Although there have been concerns about possibleenvironmental and human-health effects, forest chemi-cals generally are a minor source of water contamina-tion (Ice et al., 1998), and are generally not associatedwith cancers or genetic abnormalities in wildlife(USDA Forest Service 1984, Miller and Witt 1991).Acute and chronic doses affecting wildlife are wellabove those of normal herbicide applications inforestry, and chronic levels are not reached because ofthe low persistence of forest herbicides (Morrison andMeslow 1983). Herbicides usually degrade within daysor weeks, and they pose no significant toxic hazardwhen applied at recommended rates (Melchiors 1991).

But herbicides affect the structure and compositionof plant communities, and subsequently, wildlife habi-tat and associated wildlife communities. For example,Dickson et al. (1983, 1995b) found that herbicide-cre-ated snags increased the diversity and abundance ofbirds in young forests in eastern Texas. Increased com-plexity and abundance of understory vegetation fol-lowing herbicide application may result in increasedabundance of small mammals (McComb and Rumsey1982). Although few data are available, amphibianslikely respond to herbicide-induced changes in micro-climate such as humidity and temperature of the forestfloor.

Herbicide effects on plant community structure andcomposition, and wildlife habitat differ with the herbi-cide used and a host of other factors. For example, phy-totoxicity of tebuthiuron has been demonstrated to varywith soil texture, precipitation. and application rates(DeFazio et al. 1988). Application methods (banded,broadcast spray, pellets. injection) also can be impor-tant. Obviously, target-specific application, such asinjection or banded spraying, will have less impact onplant communities than broadcast methods.

Usually, woody vegetation is reduced and herba-ceous vegetation is increased following herbicideapplication (Hurst and Palmer 1988, DeFazio et al.1988). McComb and Hurst (1987) report that somewildlife foods, such as fruiting from shrubs, can beadversely affected by herbicide application, and some,such as grass seed, can be enhanced by it.

Increasing pine growth through herbicide applica-tion can decrease the time until the overstory canopycloses and understory cover is reduced from shading.Dalla-Tea and Jokela (1991) observed that &year-oldpine plantations receiving total vegetation controlintercepted about 60% of photosynthetically activeradiation compared to about 30% for plantationsreceiving no vegetation control.

In mid-rotation or mature forests, herbicides can beused to achieve specific structural or compositionalobjectives for wildlife. For example, herbicides can beused to reduce overstory cover, increase cover in thelower foliage levels, or alter the litter layer (McComband Hurst 1987). Snags for wildlife can be createdusing herbicides, however herbicide-created snags usu-ally deteriorate and fall in several years in the humidSouth (Dickson et al. 1995b, Cain 1996).

Even though herbicides alter plant communities,those effects often are apparent for only a few growingseasons (Hurst and Blake 1987, Copeland 1989).Miller and Chapman (1995) concluded that differencesoccurred in plant and associated animal communitiesfollowing treatment with hexazinone, imazpyr, andpicloram-+triclopyr, but those differences were short-lived, and treatment-related differences generally wereno longer evident at 5 years post-treatment.

FERTILIZATION

Forest fertilization with nitrogen or phosphorous isincreasingly common for managers seeking to increasetree growth and yield in pine and hardwood forests(Jokela and Stearn-Smith 1993). Fertilizers are com-monly applied at the time of stand establishment and atmid-rotation. Of course, productivity gains vary withsoils, application timing and rates, and other factors.

Fertilization with nitrogen has been shown toimprove first-year survival of pine seedlings by asmuch as 15% (Irwin et al. 1998). In pine stands, appli-cations of nitrogen and phosphorous produce larsrgrowth responses than applications of either elementalone. With fertilization in young stands, rapid treegrowth reduces the time until canopy closure and short-ens the rotation.

94 MANAGING FORESTS FOR WILDLIFE

Most investigations of how fertilization affectswildlife have focused on responses of deer forage. Onmany sites in the South, nutrient content and digestibil-ity of wildlife forage are limited (Blair et al. 1977).Although understory vegetation is affected by factorssuch as overstory and other conditions (Conroy et al.1982, Blair 1982), biomass and nutrient content ofunderstory vegetation generally increase following fer-tilization (Dyess et al. 1994, Haywood and Thill 1995,Hurst et al. 1982, Wood 1986). Also, studies haveshown that diversity and fruit production of selectedplant species groups are highest on fertilized sites(Camp0 and Hurst 1980). Although plant communityresponses to fertilization generally are positive, theyusually are temporary, lasting only 2-3 growing seasons(Wood 1986). Furthermore, gains in biomass and nutri-ent content may be mitigated by decreased time untilcanopy closure.

CONCLUSION

There are abundant and diverse wildlife communitiesinhabiting southern forests. These communities and thespecies comprising them are largely determined byhabitat characteristics at the landscape level and thesmaller, stand scale. Natural processes, such as plantsuccession, and the wide variety of human activitieswhich affect landscape composition and stand structure,play a large role in determining the composition andstatus of vertebrate communities of southern forests.Broad measures, such as the retention of streamsidezones, benefit a number of species, and specific meas-ures, such as species restoration, can be employed toaddress particular conservation concerns.