Original scientific paper Croat. j. for. eng. 37(2016)2 319 A Methodological Approach Exploiting Modern Techniques for Forest Road Network Planning Andrea Laschi, Francesco Neri, Niccolò Brachei Montorselli, Enrico Marchi Abstract A well-developed road network allows all forest activities, including wood harvesting, fire- fighting and recreational activities. However, forest road construction and maintenance in- volve economic and environmental costs. For these reasons, forest road network planning is a fundamental phase of forest management, maximising the benefits and reducing costs and impacts. Thanks to modern technologies in data collection both for terrestrial and forest char- acteristics, new methods and tools have been developed to improve and facilitate road planning. The aim of this study was the development of a Decision Support System for helping manag- ers during forest road network planning, exploiting Multi-Criteria Analysis, an Analytic Hierarchy Process and Geographic Information Systems. Three steps characterised the study: Þ an in-depth survey of the existing forest road network Þ an accessibility evaluation, based on a commonly applied Italian definition, taking into account the morphological characteristics of the land Þ an estimation of the accessibility requirements through the analysis of experts’ opin- ions, defined as Road Needs Index, based on different factors These phases were applied to a forest property located in northern Italy, and some improve- ments were proposed simulating a manager’s approach during planning. The results showed interesting features in accessibility evaluation, which identified three different classes of ac- cessibility, represented in a map. The estimation of Road Needs Index assigned a class regard- ing road requirements to each forest management unit: »low«, »medium«, »high« and »very high«. This information was merged, becoming a useful tool to identify the forest areas with the highest problems in relation to the forest road network. Keywords: forest management, GIS, Analytic Hierarchy Process, accessibility, road needs, Decision Support System roads allow access to remote areas in case of natural hazards (Enache et al. 2013) and are a fundamental in- frastructure in extinguishing forest fires (Hayati et al. 2012). Construction characteristics should be different, depending on the kind of machines that are expected to run on different road branches. In particular, width, slope and radius of curvature are the most important elements for forest roads that can limit vehicles traffic- ability (i.e. dimensions and payload of vehicles). The quality of roads is related to building and maintenance quality, in terms of both techniques and materials, and it can vary during road lifespan (Kiss et al. 2015). Con- 1. Introduction A sustainable perspective of forest management cannot ignore careful and accurate forest road network planning (Çalişkan 2013, Hippoliti 1997, Hippoliti 1976). A forest road network traditionally ensures ac- cess to forests and grazing lands, allowing forest op- erations and other productive activities. In the last decades, the increasing importance of the multi-func- tionality of forests has highlighted the key role of forest road management for tourism and recreational tasks (Gumus et al. 2008, Chirici et al. 2003). Moreover, forest
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Originalscientificpaper
Croat. j. for. eng. 37(2016)2 319
A Methodological Approach Exploiting
Modern Techniques for Forest Road Network Planning
Andrea Laschi, Francesco Neri, Niccolò Brachetti Montorselli, Enrico Marchi
Abstract
A well-developed road network allows all forest activities, including wood harvesting, fire-fighting and recreational activities. However, forest road construction and maintenance in-volve economic and environmental costs. For these reasons, forest road network planning is a fundamental phase of forest management, maximising the benefits and reducing costs and impacts. Thanks to modern technologies in data collection both for terrestrial and forest char-acteristics, new methods and tools have been developed to improve and facilitate road planning. The aim of this study was the development of a Decision Support System for helping manag-ers during forest road network planning, exploiting Multi-Criteria Analysis, an Analytic Hierarchy Process and Geographic Information Systems. Three steps characterised the study:
Þ an in-depth survey of the existing forest road networkÞ an accessibility evaluation, based on a commonly applied Italian definition, taking into
account the morphological characteristics of the landÞ an estimation of the accessibility requirements through the analysis of experts’ opin-
ions, defined as Road Needs Index, based on different factorsThese phases were applied to a forest property located in northern Italy, and some improve-ments were proposed simulating a manager’s approach during planning. The results showed interesting features in accessibility evaluation, which identified three different classes of ac-cessibility, represented in a map. The estimation of Road Needs Index assigned a class regard-ing road requirements to each forest management unit: »low«, »medium«, »high« and »very high«. This information was merged, becoming a useful tool to identify the forest areas with the highest problems in relation to the forest road network.
Keywords: forest management, GIS, Analytic Hierarchy Process, accessibility, road needs, Decision Support System
roads allow access to remote areas in case of natural hazards (Enache et al. 2013) and are a fundamental in-frastructureinextinguishingforestfires(Hayatietal.2012).Constructioncharacteristicsshouldbedifferent,dependingonthekindofmachinesthatareexpectedtorunondifferentroadbranches.Inparticular,width,slopeandradiusofcurvaturearethemostimportantelementsforforestroadsthatcanlimitvehiclestraffic-ability(i.e.dimensionsandpayloadofvehicles).Thequalityofroadsisrelatedtobuildingandmaintenancequality,intermsofbothtechniquesandmaterials,anditcanvaryduringroadlifespan(Kissetal.2015).Con-
Þacompleteknowledgeoftheactualconditionsofeachroadsegmentintheentirenetworkex-amined,bothintermsofconstructioncharacter-istics and maintenance conditions
developmentofaDecisionSupportSystem(DSS).Inthelastfewyears,thissystemhasmadepossibleanorganisedandintegratedoverviewofrelevantparam-etersrelatedtoforestfunctions,helpingforestmanag-ersindecisionprocesses(VacikandLexer2014).Inthiscontext,consideringthehugenumberofvariablestobeconsideredtorepresentthemaininterestsrelatedtoforestmulti-functionality,theapproachofaMulti-CriteriaAnalysis(MCA)isrecommended(Çalişkan2013,Sacchellietal.2013).Moreover,theAnalyticHi-erarchyProcess(AHP)(Saaty1980)hasbeen,andcon-tinuestobe,oneofthemostcommonDSSsindefiningthepriorityofdifferentparametersconsidered,orga-nisingtheminahierarchy(Çalişkan2013).Further-more,GeographicalInformationSystems(GISs)playakeyroleinmanaginganddisplayingterrestrialdataforspatial forestplanning(ZekiBaskentandKeles2005)andspecificallyalsoinforestroadplanning(Na-jafiandRichards2013,Hayatietal.2012,MohtashamiandBergkvist2012,Dean1997).Theseapproachesandtechnologiesarewidelyusedinforestplanningunderasustainableperspective(DuceyandLarson1999,Mi-ettinenandHämäläinen1997)withahugenumberofstudiesbasedonmulti-criteriaandhierarchicalap-proaches,alsoonthespecifictopicofforestroadplan-ning(Pellegrinietal.2013,Ghajaretal.2012,SamaniandHosseiny2010).Becauseof the integrationbe-tween terrestrial data and information included in the forestmanagementplan, a valuable roadnetworkplan,whichtakesintoaccountthemostimportantas-pectsofroadmanagement,canbedeveloped.Withsuch information, it is possible tomake informedchoicesinroadmaintenance,enhancementandbuild-ing.Tosummarise,short-termneedsshouldnotbethemaininfluenceintheconstructionofaforestroad,butthe interventionshouldbe integrated inmid/long-termplanning,tomaximisetherelatedfunctionalityandeconomicbenefits,minimisingtheenvironmentalimpacts.TheaimofthisworkwasthedevelopmentofanMCAintegratingGISandAHPtoobtainaDSSwithreliableinformationregardingaccessibilityandroadneeds,inacasestudyareainnorthernItaly.Moreover,anevaluationoftheobtainedresultswasperformed;the results were used in simulating a forest manager’s interpretationandidentifyingweaknessesintheroadnetwork.Hypothesesforenhancementandimprove-mentsintheanalysedforestroadnetworkwerede-finedandsuggestedtothemanagers.
2. Materials and methodsThestudyareawasPaneveggioforest,analpine
tionsandtheidentificationofcriticismswereaddedtothe form and then to the dataset. All of the collected informationwasimplementedonaGISplatform(bothArcGIS9.3andQGIS2.10softwarewereused)andashapefilewithup-to-dateinformationforeachroadwasobtained.Roadswererepresentedaslines,mergedbynodesineachroadintersection.ADigitalTerrainModel (DTM) and orthophotographswere helpfulduringgraphicrepresentationofforestroadstocorrecttheerrorsinaccuracymadebytheportableGPSdur-ingthefieldsurvey.Becauseofthedimensionalchar-acteristicscollected, itwaspossible toclassifyeachroadfollowingtheItalianclassificationsuggestedbyHippoliti(1976),whichisrelatedtothekindofma-chinethatcoulddriveontheroad.CharacteristicsoftheroadsarereportedinTable1.
All of the collected information was organised in a specificgeo-referreddatabase.Thetotallengthandroaddensity(m ha–1) were calculated.
sibilitywasdevelopedbymeansofGIS,thanksalsototheinformationcollectedandorganisedinthefirststepofthiswork.Firstofall,itwasnecessarytodefinethecriteriaofforestaccessibilityinrelationtoforestroads.Themethodbasedontheaccesstime,suggest-edbyHippoliti (1976),was applied indetail. Thismethodhasbeenappliedinotherstudies(Grigolatoetal.2013,CavalliandGrigolato2009,Chiricietal.2003),becauseitisfunctionalinmountainouscondi-tions, and it takes into consideration terrain slopevariations.Hippoliti(1976)definedthreedifferentac-cessibilityclassesbasedonthetimerequiredforafor-estworkertomakearoundtriponfootfromthenear-estroadtoagivenpointintheforest.Thistimewascalledthe»accesstime«.Hippolitiassumedanaveragewalkingspeedforaworkerinforestof4km h–1onflatterrain,andawalkingspeedof400ma h–1onsteepterrain,wheremaisthedifferentiallevellinginmetres.Whentheaccesstimeisupto30minutes(forgoinginthemorningandcomingbackattheendofworkday),theareaisclassifiedas»served«,whilewhenitisbe-tween30minutesandtwohours,itis»barelyserved«.Whenaworkerspendsmorethantwohoursreachingtheworksite,theareaisconsideredas»notserved«bytheforestroadnetwork.Thisconceptwasintro-ducedinthe‘70s,whenthemanpowerpriceinItalywas»verylow«.Nowadays,consideringthecostofmanpower,itisnoteconomicallyviabletospendtwohourstoreachtheworksite.Forthatreason,inthisworkHippoliti’sapproachwasmodifiedintimerang-es,reducingthemaximumaccesstimetoonehourfor
Table 1 Road classification following Italian standards
Road for trucks Road for tractorsMain Secondary
Road width
Minimum 3.5 m 3.0 m 2.5 m
Prevalent 5–6 m 4–5 m 3–4 m
Slope
Optimum 3–8% 3–8% 3–8%
Max. average 10% 12% 14%
Max. for short stretches 14% 18% 20 (25)%
Max. counter slope* 10% 12% 14%
Minimum curvature radius in hairpin turns
10 m 7 m 5 m
* counter slope is defined as a grade that is opposite to the general running grade of a road, i.e. the slope of the road section/s that tractors or trucks have to cover loaded
A. Laschi et al. A Methodological Approach Exploiting Modern Techniques for Forest Road Network Planning (319–331)
allydrawnstartingfromeachroadbranchandcon-sideringaltitudegaps(100mfor»served«and200mfor»barelyserved«areas).Oncethedraftaccessibilitymapwasmade,afieldsurveypermittedcorrectionofthemapidentifyingnaturalbarriersthatimpedeac-cesstosomeareas,e.g.cliffsanddeepgullies.Finally,theresultsweremanuallyreportedonaGISplatformtoobtainadigitalmap,comparablewiththeresultsofthe other methods.
2.2.2 »Method A« travel timeThiswas thefirstGIS approachapplied in this
Þa»weight«wasgiventoeachpixel,whichwasdetermined as the ratio between the maximum distance (dmax)onflatterrain(1000m)andthehorizontal distance (Df(p%))correspondingtothe maximum differential levelling (dmax) (»served«=100m,»barelyserved«=200m)onaterrainwiththeslopeofthepixeltakenintoaccount.Finally,theformulasforweightcalcu-lationwerethefollowing:
Þstartingfromthevectorfileoftheforestroadnetwork,arasterfilerepresentingpresence/ab-sence of roads was created
Þstartingfromtheroadraster(presence/absence)andthecost-mappreviouslycreated,applyingthe distance limits as maximum cost (1000 m and2000mfor»served«and»barelyserved«areas,respectively),theCostDistancetoolwasapplied defining the »served« and »barelyserved«areas
considerHippoliti’sdefinitionofaccessibility.Itwasimplemented tocompareaquickmethodwith theothermodelsdescribed.Itsimplydrewabufferatafixeddistancefromeachroadbranch.Severalexam-plesofthisaccessibilityevaluationhavebeendevel-opedinotherstudies,consideringdifferentdistancesinrelationtothetypeofmachinesandtechniquesap-plied.Somestudiessetauniquelimitvalue,e.g.300mwithoutslopeconsiderations(Bååthetal.2002),and3kmbutlimitedtothefirstslopeclass(max.20%)(López-Rodríguez et al. 2009).Moreover, in otherstudies,differentclasseswithavaryingdistancewereconsidered,comparingbufferswithin150,200and250metresfromtheroad(Penteketal.2008).Inthisstudy,twobufferswereapplied,thefirstinarangeof100 m from the road and the second in a range of 300m.Thefirst corresponds to the »served«area,whichwasidentifiedwiththeoperativedistancegen-erally considered for extraction with tractor andwinch.Thesecondonewasassumedasthe»barelyserved«area,whichcorrespondstotheoperativedis-tancesofalightweightcable-yarder.
2.3 Evaluation of forest road needsThankstothepreviousanalysis,theaccessibility
degreeforallforestmanagementunitswasavailable.Thiswasimportantinformation,butitneededtobeintegratedwithanotheranalysis, inatypicalMCAperspective,toobtainacompletesetofinformationusefulforroadsmanagement.Inparticular,itwasfun-damentaltosupportaccessibilityinformationwiththereal needs of roads for each forest management unit. The »needs of roads« (or »needs of accessibility«)aimedtoidentifytheaccessibilityrequirementsindif-ferentareas,concerningdifferentcharacteristicsoffor-estmanagementunitsand the relatedsilviculturalprescriptionsapplied.Effectively,forestlocatedatanaltitude close to theupper tree line,with low treegrowthandmanagedunderaprotectiveperspective,generallyrequiresaloweraccessibilitylevelthanoth-erslocatedinamorefertilearea,withhighyield,andmanagedunderaproductiveperspective.Inthiscon-text, aGIS-basedmethod for evaluating the forestneedsintermsofaccessibilitywasdeveloped.Itwasassumedthatforestoperationswouldbetheforest-relatedactivitiescharacterisedbythehighestaccessi-bility requirements, comparedwith other servicesprovidedbytheforest,andactivitiescarriedoutinsideit.Therefore,themethodologywasdevelopedconsid-eringfactorsrelatedtoforestproductivity.Ontheba-sisofPaneveggio’sforestmanagementplan,asetofdata was chosen as factors useful for determining the forest-roadneeds.Threecategorieswereidentifiedasmore suitable than the others considering their reli-abilityandtheimpactonthisstudy:growingstock(GS),sitefertilityclass(FC)andproductivepotentialindex (PPI) for high forests. Other factors were dis-cardedforspecificreasons,e.g. theannualvolumeincrement,whichshouldbeagoodindicatorcharac-terisingaforestmanagementunitintermsofproduc-tivecapacity.Inourcase,theincrementinformationpresentedsomeout-of-scalevalues,presumablyat-tributable tomistakes in reporting,whichdid notguaranteeagoodreliabilitylevel.Inparticular,thethreecitedfactorswerechosenbecause:
GS norm FC norm PPI normRNI w GS w FC w PPI= ´ + ´ + ´ (7)
where wGS,wFC and wPPI were the weights obtained for GS,FC and PPI,respectively.TheresultwasamapofthePaneveggioforestinwhicheachpixelwasclassifiedinrelationtoaccessibility
developedtoevaluatethecorrespondencerate.Inpar-ticular,themapswereoverlappedandcompared,iden-tifyingthepercentageofpixelswiththesameaccessibil-ity class assigned (correspondence) and the others,wherethemodelassigneddifferentclasses.Theresultsshowed that correspondences of 83.1%, 87.2% and51.5%werecalculatedformethodsA,BandC,respec-tively,using»MethodH«asthereference.
3.3 Evaluation of forest road needsThe AHP results defined the values for the
»weights«tobeusedintheRNIcalculation.Inpar-
Fig. 1 Paneveggio forest road network
Table 3 Surface distribution in accessibility classes identified by means of four analysed methods
»Served« »Barely served« »Not served«
»Surface« % ha % ha % ha
»Method H« 56.2 1574 20.0 562 23.8 667
»Method A« 54.7 1534 21.2 594 24.1 675
»Method B« 60.2 1689 21.4 599 18.4 515
»Method C« 26.8 750 34.2 960 39.0 1093
A. Laschi et al. A Methodological Approach Exploiting Modern Techniques for Forest Road Network Planning (319–331)
326 Croat. j. for. eng. 37(2016)2
Fig. 3 Results of »Method B« applied to Paneveggio forest
Fig. 2 Results of »Method A« applied to Paneveggio forest
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Croat. j. for. eng. 37(2016)2 327
ticular, theelaborationofexperts’answersshowedthat themost important factorwas theGS,with aweightof45%,whileweightsof30%and25%weredetermined for FC and PPI,respectively.Thefinalfor-
mulaappliedtoeachforestmanagementunitincal-culating the RNIwas:
SummarisedinformationonRNI distribution of thetotalsurface,alsoinrelationwiththecurrentac-cessibilityresults,isreportedinTable4.Fig.6givesagraphicalrepresentationoftheRNI
Table 4 Forest area distribution based on RNI. For each RNI class, the distribution of the area in each of the current accessibility classes is shown
Total
At-present accessibility class
»Served«»Barely served«
»Not served«
Road
Nee
ds In
dex
»Low«ha 75.7 0.0 22.4 53.3
% 2.7 0.0 0.8 1.9
»Medium«ha 765.2 185.0 238.3 341.9
% 27.3 6.6 8.5 12.2
»High«ha 1202.5 857.7 274.7 70.1
% 42.9 30.6 9.8 2.5
»Very High«ha 759.6 644.7 64.5 50.4
% 27.1 23.0 2.3 1.8
Fig. 4 Results of »Method C« applied to Paneveggio forest
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328 Croat. j. for. eng. 37(2016)2
Fig. 5 Results of »Method H« applied to Paneveggio forest
Fig. 6. Distribution of forest management units in classes depending on RNI
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curvaturesandslope;only6%ofroadscouldallowthetransitofheavytrucks.Thisinformationshouldsug-gest the enhancement of the main forest roads to im-proveandrationalisewood transportbymeansofheavytrucksinsteadoftractorsandtrailers.Theslopeisacrucialfactorinaccessibilityestimation.Inmoun-tainousareas,theslopeheavilyinfluencestheacces-sibility(CavalliandGrigolato2009)andstronglyaf-fectstheloggingsystemandcostsofforestoperations(Hippoliti1997).Inthisstudy,theaccessibilityanalysisaddedessentialinformationregardingtherationalityinforestroadsdistributionaroundtheforestproperty.Comparingtheappliedmethods,»MethodC«showedtheworstperformance,intermsofcorrespondence,incomparisonwith resultsobtainedby»MethodH«,whichwastakenasthereference.»MethodsA«and»B«hadsimilarresponses;»MethodA«obtainedbet-terresultsthan»MethodB«consideringthegeneralsurfacepercentageallocatedtothethreedifferentcat-egories,whichwereverysimilarinvalueto»MethodH«.Ontheotherhand,»MethodB«showedbetteraccuracy than »MethodA«, considering the corre-spondenceinpixelallocation.Thissimilaritywasex-pected,consideringthesimilarapproachusedinthetwomethods.However,accuracywasconsideredasthemainobjectiveinidentifyingthebestmethodfor
accessibilityestimation,and»MethodB«hadthebet-terperformanceinthissense.Itshoweda»high«rateof»served«managementunitsinPaneveggioforest(about60%ofthetotal)andalimited»notserved«area(18%).Inthiscontext,introducingtheevaluationoftherealneedsofforestroadsindifferentareas,especiallyregarding»barely«and»notserved«areas,couldgiveanaddedvaluetotheroadsplanningprocessaccord-ingtothemulti-criteriaapproach.AsreportedinTable4,»notserved«areasmainlyreferredtoforestmanage-mentunitswitha»low«or»medium«RNI,whileonlyalimitedareawith»high«and»veryhigh«needswas»notserved«.Regarding»barelyserved«managementunits,therewasareasonablerateofforestwith»me-dium«and»high«RNI.Inthiscase,anenhancementoftheroadnetworkshouldimproveaccessibilitycon-ditions,optimisingproductivityinforestoperations.RegardingthethreefactorsanalysedintheAHP,tech-niciansfocusedtheirmaininterestongrowingstock(weight:45%),whichisafactorinfluencingshort-termdecisions.Fertilityclasshadanintermediateweight(30%),thushighlightingtheattentionofforesttechni-ciansalsoonlong-termaspects,whiletheproductivepotentialindex(25%)receivedaquitelowweight.Inpractice,RNIanalysistookintoaccountabalancedmix of information aimed both to short and long-term
Fig. 7 Proposals for two new forest roads
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330 Croat. j. for. eng. 37(2016)2
approachesforforestroadnetworkplanning.How-ever,themethodcouldbeimprovedthroughtheim-plementationofmore,ordifferent,factors;inparticu-lar,theincrementsofvolumeshouldbeconsideredwhenavailabletoobtainarepresentativeparameterrelatedtostandproductivity.Moreover,inRNIanaly-sis,differentsolutionsoralternativescouldbeimple-mentedtooptimisethemethodsdependingonman-agement priorities. In the case of special needs,specificfactorscouldbeintroducedintotheRNI cal-culation formula,enlarging theanalysis to specifictopics.Anexampleofthatwouldbetheuseofindica-torsregardingwildfirerisk,ortourismpointsofinter-est.Inthesecases,theRNIanalysiscouldgiveusefulinformationinadditiontotheordinaryneeds,nor-mallysatisfiedwhentheroadnetworkisfunctionalforforestoperations.
improveforestroadnetworkplanningwasdevelopedandappliedtoaforestproperty.MCAandAHPcrite-riawereappliedbymeansofGIS,exploitingterres-trialinformationandforestcharacteristics.Thestateandaccessibilityrequirementsinaforestareahavekeyrolesinoptimisingroadnetworkmanagement.Theanalysisdevelopedinthisstudycouldbearealaddedvalueformanagersduringplanning.Inpar-ticular,theexaminedmethodsfacilitateobjectivefor-estroadplanning,whichpermitsoptimisationofre-sourcesandavoidsthebuildingofauselessroadand/oroversizedroadnetwork.Enhancementoftheforestroadnetwork,throughwell-definedimprovements,guaranteesthecorrectmanagementoftheforest,al-lowingalloftheforestservices,suchaswoodproduc-tion, hydrogeological protection, tourism use andhabitatconservation.Inpractice,awell-plannedandwell-realisedroadnetworkmaximisestheefficiencyofallforestactivities,minimisingthecosts,botheco-nomically and environmentally. The approachde-scribedandachievedinthisstudyperfectlyfitinthisperspective,reportingfundamentalinformationuse-fulforsustainablemaintenanceanddevelopmentoftheforestroadnetwork.
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