Effects of Rubber-Tired Cable Skidder on Soil Compaction ...

Originalscietificpaper–Izvorni znanstveni rad

Croat. j. for. eng. 34(2013)1 123

EffectsofRubber-TiredCableSkidder

onSoilCompactioninHyrcanianForest

BarisMajnounian,MegdadJourgholami

Abstract – Nacrtak

The use of skidders equipped with rubber tires is a well accepted practice for the extraction of timber from the forest, but the application also causes considerable environmental problems. The aim of the study was to evaluate the effects of different slope gradient, number of machine passes on skid trails and soil depth on soil compaction. The study was designed as an experi-ment with the factors including slope gradient, soil moisture, and soil depth on various skid trails and with different number of machine passes. The effects of four slope classes (flat, 10%, -10% and -20%), three soil depth classes (5, 15 and 25 cm), and different compaction levels based on various number of machine passes (0, 1, 5, 8, 10, 15, 20, 25 and 30) were evaluated. A Timberjack cable skidder was used and the study location was in the Kheyrud Educational and Research Forest located in the Hyrcanian forest in northern Iran. The increased number of machine passes increased soil bulk density, but the highest rate of compaction occurred after the initial few passes. Uphill skidding increases soil compaction more than downhill skidding. The increases in bulk density were still significant at the maximum sampling depth of 20–30 cm. Soil bulk densities at 5, 15 and 25 cm depth averaged 35, 22 and 17% higher than densi-ties of undisturbed soil.

Keywords: soil compaction, soil bulk density, rubber-tired cable skidder, Hyrcanian forest.

1. Introduction – UvodForestsoils,ingeneral,aresusceptibletocompac-

tionastheyareloosewithhighorganic-matter,andaregenerallylowinbulkdensity,highinporosity,andlow in strength (Froehlich et al. 1985;Kolkaa andSmidt2004).Theimpactofskiddingoperationsonfor-estsoilscanbedividedintothreemajorcategories:soilprofiledisturbance,soilcompactionandsoilpuddlingandrutting(Rabetal.2005).Whenamechanicalloadisappliedtothesoil,soil

particlesarerearrangedclosertogetherresultinginin-creasedbulkdensity(massperunitvolume)(Cullen1991;Eliasson2005;Graceetal.2006),reductionofthetotalporosityassociatedwithareductionofmacro-pores(GayosoandIroume1991;Gomezetal.2002;Aresetal.2005),increaseinsoilstrength;exceptforsoilwithlowbearingcapacities(Hornetal.1994),decreasedin-filtrationcapacity(Hornetal.1994,2004),decreasedgaseousexchangeandsoilaeration(Hornetal.1994),anincreaseinresistancetopenetration(Ampoorteretal.2007),decreaseinsaturatedhydraulicconductivity

(GreacenandSands1980;Hornetal.1994;Graceetal.2006),andincreasedmicroporeproportion(KolkaaandSmidt2004).Oneofthemajorimpactsofharvestingoperationsissoilprofiledisturbance.Soildisturbanceisusuallydefinedintermsofmixingand/orremovaloflitterandsoil,whichmaychangethephysical,chemicalorbiologicalpropertiesofsoil(Rabetal.2005).Depend-ingontheequipmentused,thesurfacesoilsarevari-ouslymixed,buriedorinverted.Duringtimberharvestingthedegreeofsoilcompac-

tiondependsonvariousfactorsincluding:siteandsoilcharacteristics(AdamsandFroehlich1984;Ampoorteretal.2007)suchassoiltexture(Froese2004;Rohandetal.2004),soilmoisture(Johnsonetal.2007),thenumberofmachinepasses(Eliasson2005;Šušnjaretal.2006;Ampoorteretal.2007;EliassonandWasterlund2007;Wangetal.2007)andharvestingsystem.Inaddition,themachinecharacteristicsaffectingthedegreeofsoilcompactionincludetypeofmachine(Šušnjaretal.2006;Wangetal.2007),massofvehicleandload(Rab1996;Saarilahti2002;Šušnjaretal.2006;Hornetal.2007),type,numberofwheelsandinflationpressureofthe

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124 Croat. j. for. eng. 34(2013)1

tires(Ziesak2006),amountofloggingslash(WronskiandMurphy1994;EliassonandWasterlund2007).Acoupleofstudiesreportedbyseveralresearchersshowthatoneofthecriticalfactorsaffectingthedegreeofsoilcompactionisthenumberofmachinepassesoveraspecificpoint.Thesestudiesshowthatmostcompac-tionoccursduringthefirsttenpassesofavehiclewiththemostoccurringinthefirstthreepasses.Subsequentpassesgenerallyhavelittleadditionaleffect(Ampoort-eretal.2007).Mostcompactionoccurredaftertheinitialfewpasses(MatangaranandKobayashi1999),butbulkdensityalsoincreasedsignificantlyaftermorethan3passes(GayosoandIroume1991;Eliasson2005;Elias-sonandWasterlund2007).MatangaranandKobayashi(1999)foundthatthebulkdensityincreasedmarkedlybythefirstandsecondpassofthetractor,butdidnotchangeafterthefifthpass.Fewstudieshavedocumentedslopegradientof

traileffects(longitudinalandtransversalslopeoftrail)ontheextentanddegreeofsoilcompactionanddis-turbance.Kragetal.(1986)showedthatduringtimberharvesting,slopesteepnesshadastrongereffectthanseasonofloggingonsoildisturbance.Understeepter-rainconditions,themachineslippedcontinuouslyandremainedinagivenplaceforalongerperiodoftime,puddlinganddraggingthesoil(GayosoandIroume1991).SidleandDrlica(1981)foundthattheslopedidnotsignificantlyaffectbulkdensity,buttheyconclud-edthatitcanbeanimportantfactorinthepotentiallevelofcompaction.Jamshidietal.(2008)foundthattherewasnodetectabledifferenceincompactionbe-tweenmachineskiddingonflattrailsandtrailswithlongitudinalgradientortransversalslope.Compactedlayersareoftenfoundatdifferentsoildepths.How-ever,thedeeperlayersofmanysoilsarecompactedfurtherafterafewpasses.Thevaluesofthesoilbulkdensitymostlydependonthequantityoforganicmat-ter.Inthesurfacehorizons,thesoilbulkdensityislow,andaswiththeincreaseofdepth,organicmatterisrapidlydecreased,thebulkdensityincreasesinsub-soil(FroehlichandMcNabb1984).Increasesinorgan-icmatterreducesoilcompactibility(Kozlowski1999).Astrongincreaseinbulkdensityismostdistinctintheupper20cmofthesoil,sincetheexertedpressureismaximalatthesoilsurfaceanddeclineswithincreas-ingdepthasthetotalpressureisspreadoutoveranenlargingarea(GentandMorris1986;Ampoorteretal.2007).Johnsonetal.(2007)notedthatsoilcompac-tionwasgenerallylimitedtoskidtrailsandtopsoillayers(<30cm).EliassonandWasterlund(2007)re-portedthatanincreasednumberofmachinepassagesincreasedsoildrydensityintheupper20cm.TheHyrcanianmountainous forest innorthern

Iranisrichinbiologicaldiversity,withendemicand

endangeredspecies,andadiverserangeofeconomicandsocialconditions.IntheHyrcanianforest,afewstudieshavebeencarriedoutabouttheeffectsofforestoperationsonsoilcompactionandbulkdensity.Jam-shidietal.(2008)measuredthechangesinbulkden-sityinthetop10cmofsoilfollowingmachineandanimalskiddingintheHyrcanianforest.Theyfoundthattheaveragesoilbulkdensityinthetracksofma-chineskidtrailswassignificantlygreaterthanthesoildensity outside the tracks, but the increase in bulk densitywasnotsignificantontheanimaltrails.Theextentoftheseveredisturbancefromground-

basedharvestingsystemsvariesdependingonslopeandsteepterrain,althoughtheeffectsofslopeonsoildisturbanceandbulkdensityhavereceivedlessatten-tion.Thespecificobjectiveswereto:quantifytheex-tentoftrailareaandwinchingline(disturbancearea)throughouttheharvestunit,tocharacterizeandestab-lishthethresholdlevelsforthemachinetrafficwithrespecttobulkdensityandslopegradientordirectionofskiddingforthreedifferentsoildepths.

2. Materials and methods – Materijal i metode

2.1 Study site – Područje istraživanjaAbout65%oftheHyrcanianforestsarelocatedin

mountainousareaswithterrainslopeofmorethan27%(Fig.1),whereforestlandsarenotreadilyacces-

Fig. 1 Proportion of the Hyrcanian forest area based on terrain slopeSlika 1. Udio nagiba terena šumskih zemljišta Hirkanijske šume (Golestan)

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Croat. j. for. eng. 34(2013)1 125

siblewith ground-based logging equipments. Thecableyardingtechnologiesarestillundevelopedinthisforestarea.TheresearchwascarriedoutincompartmentNo.

220,whichislocatedinNamkhanehDistrictwithinKheyrudEducationalandResearchForestintheHy-rcanianforestofnorthernIran(Fig.2).Thealtituderangesfrom1000to1135mandtheforestliesonasouthwesternaspect.Theaveragerainfallrangesfrom1420to1530mm/year,withtheheaviestprecipitationoccurringinthesummerandfall.Theaveragedailytemperaturerangesfromafewdegreesbelow0°C in December, January,andFebruary,andup to+25°C duringthesummer.Thisareaisdominatedbynaturalforestscontainingnativemixeddeciduoustreespeciessuch as Fagus orientalis Lipsky, Carpinus betulus L.,Acer velutinum Boiss.andAlnus subcordata.Themanage-mentmethodismixedun-evenagedhighforestwithsingleandgroupselectivecuttingregime.Thesoilofthestudysiteisclassifiedasabrownforestsoil(Alfi-

sols)andwell-drained.Thetextureofthesoilrangesfromsiltloamtoloamy.Treestoberemovedwerefelled,limbedandtopped

motor-manually.Felled treeswerebuckedandpro-cessedwith chainsaws into logs, sawn-lumber andpulpwood.Thelogsof5–15meterlengthwereextract-edbyrubber-tiredskidderstotheroadsidelandings.Thefuelwoodwasextractedbymules.Also,insteepterrain that could not be reached by skidders, logs were processedtosawn-lumberandthenhauledbymules.Animportantstrategyistolimittrafficondesignatedskid trails, hence, landings and skid trails were clearly flaggedonthegroundbeforeharvesting.Theintensionwas to require the skidder to stay on the skid trail and winchlogsonthetrail.Downhillanduphillskiddingtothelandingwasplannedwithoutanyexcavationandtheskiddingoperationsweredoneonnaturalground.Theextractiondistancestotheroadsidelandingwas780m.Theskidtrailsloperangesfrom0to35%.Table1presentssomecharacteristicsofthestudysite.

Fig. 2 Location of study site within the Hyrcanian ForestSlika 2. Područje istraživanja

Table 1 Characteristics of the study siteTablica 1. Značajke istraživanoga područja

Area, ha

Površina, ha

Tree per ha

Broj stabala po ha

Volume, m3/ha

Obujam, m3/ha

Total removed trees

Ukupno posječeno stabala

Total volume of removed trees, m3

Ukupni drvni obujam, m3

DBH of removed trees, cm

Raspon prsnih promjera posječenih stabala, cm

17 173 504270

(10 tree/ha – 10 stabala/ha)872.3 (32 m3/ha) 20–135

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2.2 Experimental design and data collection Plan istraživanjaFellingofmarkedtreeswascarriedoutinMarch

andskiddingoperationsweredoneinAugust2008.Atthetimeofharvesting,weatherconditionswereverydryandwarmformorethan5weeksandtheseconditionsremainedconstantduringskiddingopera-tions.Fig.3presentsthe4WDTimberjack450Crub-ber-tiredskidderusedinthestudy.Thismachineisnormally an articulated, four-wheel-drive vehicleweighing10.3ton(55%onthefrontand45%ontherearaxle)withenginepowerof177hp(132kW)andenginemodelof6BTA5.9.Itisequippedwithabladeforlightpushingofobstaclesandstackingoflogs.Theskidderwasfittedwith24.5–32tiresinflatedto220kPaon both front and rear axles, and it had a ground clear-anceofapproximately0.6mwithoverallwidthof3.1m.Timberbunchingwascarriedoutbythewinchin-stalledintherearpartoftheskidderfromthestumpto the skidder and one end of the round wood was draggedontheground.Inthestudyareas,theaverageloggedvolumeineachpasswas3.5cubicmeters(1and3logs,respectively).Twelvesamplingtransectswereselectedatdiffer-

entslopegradientsalongthedesignatedskidtrailforbulkdensitymeasurements(Fig.4).Organichorizonswereremovedfromthesoilsurfacepriortodensitymeasurements,sothatdepthreadingswerereferencedtothemineralsoilsurface.Inordertoensurethatthemeasurementsweremadeinthesameplaceafteracertainnumberofpasses,wehaveputthepaintedsticksinthecenterofskidtrails.Thepaintedsticksindicatedthecentersoftheexperimentalskidtrailsattheskidtrial,sothatthemachineswouldfollowthe

sametracksatsubsequentpasses.Beforeskidding,fourslopegradientswereestablishedintheskidtrailwith3replicationsindisturbedareasat0–10cmsoilprofiledepth,andthedifferentlevelsofcompactionwereappliedbyvaryingthelevelsofmachinetraffic:0(undisturbed),1,5,8,10,15,20,25and30machinepasses.Apassimpliesadrivebackandforththese-lectedtrail.Fourslopegradientsofskidtrailwere0(flattrail),10%,–10%and–20%.Also,priortoanyskiddingoperationsandafter20machinepasses,bulkdensitywasmeasuredatthisfourslopegradienttrail(flattrail,10%,–10%and–20%)atthe5cm,15cmand25cmsoilprofiledepthsinwheelrut(AandB)andcontrolsamplepoint(Fig.4)ontheadjacentskidtrail

Fig. 3 Timberjack skidder, equipped with rubber-tires while extract-ing timberSlika 3. Skider Timberjack prilikom privlačenja drva

Fig. 4 Sketch of study layout for soil samplingSlika 4. Shema rada za uzimanje uzoraka tla

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(C).Thesoilsamplecoreswereobtainedfromthelay-ersofthemineralsoilusingathinwalledsteelcylin-der,40mmlongand56mmindiameter,insertedintothesoilbyahammer-drivendevice.Afterextractingthesteelcylinderfromthesoilwithminimaldistur-bance to thecontents, thesoil coreswere trimmedflushwiththecylinderendandextrudedintoaplasticbagfortransportingittothelaboratory.Sampleswereweighed on the day they were collected and again af-terovendryingat105°Cfor24htodeterminewatercontentandbulkdensity.Inordertodeterminetheextentofdisturbancefrom

skidderoperations,disturbedwidthsweremeasuredat25mintervalsalongtheskidtrails.Skidtrailsoildisturbancewasclassedas:A-horizonpuddledandmixedwithforestfloororganicdebris,andsomeA-horizonremovedandtherestmixedwithB-horizon.Alsolandingareasweremeasuredinthecompartment.Log winching, however, cause the excavation of the line betweenstumpsnearthevehicle,hence,fordetermin-ingthisdisplacement,totallengthandwidthofwinch-inglinesinbothsidesoftrailsweremeasured.

2.3 Statistical analysis – Statistička obrada podatakaTheexperimentaldesignwasafactorialarrange-

mentoftreatmentsconductedinacompletelyran-domizeddesign.Generallinearmodeling(GLM)wasappliedtorelatebulkdensityandrutdepthtoma-chinepasses,slopegradient,anddepthinrelationtotheskidtrails.Post-hoccomparisonofmeanswasper-

formedusingDuncan’smultipledesigns tomean-basedgroupingwitha95%confidencelevel.AnalysisofvarianceofthedatawasconductedinSPSS(release15.0)toidentifydifferencesbetweenbulkdensityval-uesoffourslopegradientsinskidtrails.TreatmenteffectswereconsideredsignificantifP<0.05.Soilbulkdensitybeforeandafterskiddingoperationswascom-paredusingindependentsamplest-test.Also,one-wayANOVAwasperformed.

3. Results – Rezultati

3.1 Soil disturbance – Oštećenje tlaA detailed survey of the harvested unit following

extractionwithacableskidderindicatedthat5.8%ofthetotalarea(17ha)wascoveredwithskidtrailsandanadditional0.8%oftheunitwasoccupiedbythelanding(Table2).In this study,ground-basedwinchingof timber

fromthefellingsitetotheskidderhadsubstantialef-fectonsoildisplacementthatoccupied0.9%ofthetotalarea.Withthewholeloadlyingontheground,duringwinchingitremovedandpushedalayerofsoilinfrontofitself.Finally,inthisstudy7.5%ofthehar-vestingtotalareawasdisturbedandcompacted.Thedisturbancewidthofthetrailwassignificantlyinflu-encedbytransversalslopegradientsoftrails.There-fore,thehighertransversalslope,thewideristhetrailwidth.Therewerethreemainskidtrailsintheharvestareawithatotallengthof1971meters.Theaverage

Table 2 Compartment disturbance area due to rubber-tired skidder operationTablica 2. Oštećenje tla nastalo pri radu skidera

Factor

Mjesto

Trail length, m

Duljina vlake, m

Trail average width, m

Prosječna širina vlake, m

Disturbed area, m2

Oštećena površina tla, m2

Landing area, m2

Pomoćno stovarište, m2

Winching line, m

Duljina privitlavanja, m

Line width, m

Širina traga privitlavanja, m

Winching disturbed area, m2

Površina tla oštećena skupljanjem drva, m2

Total disturbed area, m2

Ukupno oštećena površina tla, m2

Trail 1

Vlaka 1324 4.8 1555.2 1150 241 0.32 77.12 –

Trail 2

Vlaka 21387 5.1 7073.7 – 3752 0.34 1275.68 –

Trail 3

Vlaka 3260 4.95 1287 180 380 0.29 110.2 –

Total area

Uk. površina1971 – 9916 1330 4373 – 1463 12709

Area, %

Površina, %– – 5.8 0. 8 – – 0.9 7.5

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was5meters,andsooccupied5.8%ofthetotalarea.4373metersofwinchlinedisturbancewasrecordedwithanaveragewidthof0.315metersforatotalof0.9%ofthearea.

3.2Soilcompaction:influenceofslopesandmachine passes – Zbijanje tla: utjecaj nagiba terena i broja prolazaka vozilaTable3showstheanalysisofthesoilbulkdensity

datainfluencedbymachinepassesandslopegradient

forthecableskidder.Theresultsshowedthatmachinepassesandslopegradient,andtheinteractioneffectsofmachinepasses×slopegradientwereallsignificantvariables(P<0.05).Theindependentsamplest-testindicatedthatskid-

dinghadastatisticallysignificanteffectonthebulkdensityofsoilontrailsbeforeandaftermachinepassesineachtrailwithdifferentslopegradientsandbyinde-pendentsamplest-testandDuncan’stest(b).Thevaluesaremean.Differentletterswithineachslopetreatmentshowsignificantdifferences(P<0.05)(Fig.5).Theresultsshowthatbulkdensitysignificantly

increasedasthenumberofmachinepassesincreased(Fig.6).Regardlessoftheslopegradient,thedegreeandlevelofcompactiondifferedamongtrailslopeus-ingDuncan’smultiplerangetest(Fig.7andTable4).InTable4,foreachsoilintervalmeansarecomparedagainsteachotherafterANOVAusingDuncan’stest.Valuesaremean.Thedifferencebetweenvaluesinacolumnfollowedbydifferentsuperscriptsissignifi-cant at P<0.05.Intheotherhand,generally,trailswithfourslopes

showasimilartrendofincreasingsoilbulkdensitywithincreasingamountsofmachinepasses.Inflattrail,thebulkdensityinthetop0–10cmofsoil(1.06g/cm3)in-creasedby5%after1pass,19%after5passes,25%after8passes,31%after15machinepasses.Intrailwitha10%slopeoruphillskidding,thesoilbulkdensityin-

Table 3 Analysis of variance (ANOVA) for the effect of number of machine passes (NP) and slope gradient (SG) on bulk density in 0–10 cm soil depthTablica 3. Analiza varijance za prolazak vozila (NP) i nagib terena (SG) na dubini tla do 10 cm

Source

Izvor podataka

Sum of Square

Zbroj kvadrata

df

Mean Square

Srednja kvadratna vrijednost

F-value

F vrijednost

P-value

P vrijednost

NP 1.77 8 0.221 829.34 0.00

SG 0.17 3 0.058 216.36 0.00

NP × GS 0.06 24 0.003 9.67 0.00

Fig. 5 Average bulk density (a) and its relative changes before and after skidding in each slope gradient of the trail and by independent samples t-test and Duncan’s test (b)Slika 5. Prosječne vrijednosti (a) i relativne promjene gustoće tla nakon privlačenja drva (b)

Fig. 6 Relationship between the increase of bulk density (%) and machine passesSlika 6. Odnos povećanja u gustoći tla (%) ovisno o prolasku vozila

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creasedby19%after1pass,43%after5passes.Subse-quentincreaseofthenumberofpasses(upto30turns)didnotincreasethebulkdensitysignificantly.Highlevelofincreaseinbulkdensityoccurredafter5ma-chinepassesandadditionalincreaseofpassesdidnotincreasethebulkdensitysignificantly.Intheareawith-10%,bulkdensityincreasedby9%after1pass,25%

after5passes,34%after8turnsandintrailwith-20%slope,by9%after1pass,22%after5passes,29%after8turnsand34%after10passes.Inflattrail,thehighestrateof compaction, asbulkdensity increased, tookplaceduringthefirst15passesby1.37g/cm3.Intrailwith10%slopegradient,incontrast,highincreasewasobservedinbulkdensity(1.44g/cm3)anditoccurred

Fig. 7 Relationship between the increase of bulk density and machine passes on different slope gradientsSlika 7. Odnos povećanja u gustoći tla s prolaskom vozila na vlakama različitih nagiba

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after5machinepasses.Also,indownhillskiddingwith–10%and–20%,bulkdensitieswereincreasedsignifi-cantlyafter8and10machinepasses,respectively.Then,soilbulkdensityfor–10%and–20%was1.41and1.41g/cm3,respectively.Bulkdensityinthe10%trailshowedthehighestvalueincomparisonwithotherslopegradientsofthetrail(Fig.5).Skiddingoperationsalongflattrailhadthelowestcompaction(Duncan’s).

3.3Soilcompaction:influenceofslopesandsoildepths – Zbijanje tla: utjecaj nagiba terena i dubine tlaTable5showstheanalysesofthesoilbulkdensity

dataas influencedbyposition, slopegradientanddepthafter20machinepasses.Theresultsshowedthatposition,depth,slopegradient,andtheinteractionef-fectsofposition×slopegradientandposition×depthwereallsignificantvariables(P<0.05).GeneralLinear

Model (GLM) indicated twosignificant interactionterms,andnamelyposition×slopegradient(p<0.01)andposition×depth(p<0.01).Itcanbenoticedthatbulkdensityvaluesofcontrolsamplepoints(nopass)infourslopegradientsareclearlylessthancompactedvalues.Theinteractionbetweenpositionanddepthwasalsosignificant.Averagepre-harvestbulkdensitiesforthreesoil

depthclasses,0–10cm,10–20cm,and20–30cmwere1.06g/cm3,1.27g/cm3,and1.42g/cm3,respectively.After20machinepasses,bulkdensity increased indepthundertheskidtrailsinallslopegradientsoftrails,butthemajorincreaseoccurredinthetopofthesoilprofileat0–10cm.Inflattrail,bulkdensityin-creasedby30%in0–10cmdepth,by20%in10–20cm,andby17.5%in20–30cm,after20machinespasses.Intrailswitha10%slope,theincreaseinbulkdensityforalldepthswassignificantlyhigherascompared

Table 4 Mean bulk density values (± standard deviation) as influenced by machine passes and slope gradientTablica 4. Srednje vrijednosti gustoće tla (± vrijednost standardne devijacije) pod utjecajem prolazaka vozila i nagiba terena (SG)

SG (%)Number of machine passes – Broj prolazaka vozila

0 1 5 8 10 15 20 25 30

-10 1.08±0.01a* 1.17±0.01b 1.33±0.01b 1.42±0.02b 1.42±0.01b 1.43±0.01b 1.43±0.02b 1.44±0.02b 1.44±0.02b

-20 1.05±0.03ab 1.14±0.01c 1.27±0.02c 1.34±0.01c 1.39±0.03b 1.39±0.02c 1.4±0.01c 1.4±0.02c 1.41±0.01c

0 1.06±0.03ab 1.11±0.01d 1.25±0.02c 1.31±0.02c 1.34±0.02c 1.37±0.02c 1.38±0.01c 1.39±0.01c 1.39±0.01c

10 1.03±0.01b 1.22±0.01a 1.46±0.02a 1.46±0.02a 1.47±0.01a 1.47±0.03a 1.47±0.01a 1.48±0.01a 1.48±0.01a

Table 5 Analysis of variance (ANOVA) for the effect of sample position, slope gradient, and depth on bulk density in skid trialsTablica 5. Analiza varijance (ANOVA) podataka nagiba terena, dubine tla, gustoće tla i mjesta uzimanja uzoraka na traktorskim vlakama

Source

Izvor podataka

Sum of Square

Zbroj kvadratadf

Mean Square

Srednja kvadratna vrijednost

F-value

F vrijednost

P-value

P vrijednost

Slope – Nagib terena 0.012 3 0.004 3.78 0.02

Position – Položaj 1.611 1 1.611 1528 0.00

Depth – Dubina tla 1.035 2 0.518 491 0.00

Slope * Position

Nagib terena * Položaj0.021 3 0.007 6.59 0.00

Slope * Depth

Nagib terena * Dubina tla0.003 6 0.001 0.48 0.82

Position * Depth

Položaj * Dubina tla0.046 2 0.023 21.7 0.00

Slope * Position * Depth

Nagib terena * Položaj * Dubina tla0.001 6 0.00 0.21 0.97

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withthoseobservedintrailswith–10%,–20%slope,andflattrail.Fig.8showshowtherelativechangeinbulkdensityvariedwithslopetrailinsoildepth.Intrailwith10%slope,bulkdensityincreasedby42%in0–10cmdepth,by28%in10–20cm,andby20%in20–30cm,after20machinepasses.Theindependentsamplest-test indicated that skidding had a statisti-callysignificanteffectonthesoilbulkdensityontrailsbeforeandaftervehiclepassesinsoildepth(p<0.05).Deeperinthesoilprofile,differencesbetweencontroland the treatments in four slope gradient becamesmaller.Thehighestlevelofincreaseinbulkdensitywasfoundin the trailwith10%slopegradientbe-tweencontrolandthetreatments.Forthesoilbulkdensitysamplesinfourslopegra-

dient,one-wayanalysisofvariance (ANOVA)andDuncan’stestwereusedtoseeifthereweresignificantdifferences(P<0.05)betweenthesoildepths.Inflattrailbeforeandafterskidding,bulkdensityincreasedsignificantlyinalldepths(Fig.9),buttherewerenosignificantdifferencesbetweensoildepthsat10–20cmand20–30cmintrailswithuphill(10%)anddownhill(–10%and–20%)slopegradient.Withrespecttothebulkdensityvaluesfordifferenttrails,smallervaluesweregenerallyobservedcomparedwithuphillanddownhillskiddingforflattrail.However,apeakcanalsobeseeninthedepthintervalof20–30cm.Also,10%trailresultedinthehighestbulkdensityvaluesforalldepths,whileflattrailshowedthesmallestde-greeofcompaction.

4. Discussion – Rasprava

4.1 Soil disturbance – Oštećenje tlaOncethesamplingmethodwasestablished,the

soil disturbance survey was both quick and easy to complete.Inthisforestwhereskiddingiscommon,theskidtrailpatternisdistributedunevenlybecauseofterrainsteepness.Usingadifferentsamplingmethodin this situation did not result in an exactly accurate surveyandhadmanyoverestimations.Comparedtootherstudies(FroehlichandMcNabb1984;Rabetal.2005;Šušnjaretal.2006),soildisturbanceinthisstudyoccupiedlessthan8percents.ThisagreedwithElias-son(2005)whofoundthatsoildisturbancewillbeaf-fectedbyseveralfactorssuchaswheelslip,vibrationandnumberofvehiclepasses.

4.2Soilcompaction:influenceofslopesandmachine passes – Zbijanje tla: utjecaj nagiba terena i prolaska vozilaTheresultsshowthattheaveragebulkdensitysig-

nificantlyincreasedaftertheoperationofrubber-tiredskidders.However, indifferentslopegradientper-centages, the increased bulk densities were statisti-callydifferent.Theresultsofmoststudieswerecon-sistent with our results (Sidle and Drlica 1981;FroehlichandMcNabb1984;GayosoandIroume1991;Eliasson2005;Šušnjaretal.2006;Ampoorteretal.2007;EliassonandWasterlund2007;Hornetal.2007;Jamshidietal.2008).Also,Hornetal.(2007)showedthateachstressappliedatthesoilsurfaceisalwaystransmittedthree-dimensionallyandcausesnotonlysoilcompactionbutalsosheareffects.Theresultsshowthatbulkdensitysignificantly

increasedwiththeincreaseofvehiclepasses.Ingen-eral,trailswithfourslopesshowasimilartrendofincreasingsoilbulkdensitywiththeincreasingnum-berofvehiclepasses.Formosttreatments,thehighestrates of increase in bulk density were achieved in the first5to15vehiclepasses.Beyond15vehiclepasses,therewasusuallyverylittleincreaseinbulkdensity(MatangaranandKobayashi1999).Intheflattrail,theskidderoperatorusedthewholewidthoftheroadinsteadoftravelinginthesamewheeltracks.Impactsofthefrequencyofvehiclepassesonsoilcompactionshowedsimilarresultsinmanyresearches(SidleandDrlica1981;GayosoandIroume1991;Ampoorteretal.2007;Jamshidietal.2008).ThisagreedwithWangetal.(2007)andHornetal.(2007)whobothclaimedthatsubsequentvehiclepassesincreasedthesoilcom-pactionatalesserextentuntilthereislittleornomorecompactionassociatedwithfurthervehiclepasses.

Fig. 8 Average decrease in bulk density with soil depth on skid trails of four slope gradientsSlika 8. Prosječno smanjenje gustoće na različitoj dubini tla

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Inthisstudy,flattrailshadthelowestbulkdensity,thetrailswith-10%and-20%slopegradient(downhillskidding)hadintermediatebulkdensityandthetrailswith10%slopegradient(uphill)hadthehighestcom-paction.Thisresultcanbeexplainedbasedontheun-evenloaddistributionbetweenthedownhillandup-hilltiresoftheskidder(Jamshidietal.2008).Anotherreasonforlowerbulkdensityatthedownslopetrack

Fig. 9 Mean bulk density depending on different sampling placesSlika 9. Srednje vrijednosti gustoće tla ovisno o mjestu uzimanja uzorka

mightbethedraggingofthelogsonorclosetothistrack.Draggedbehindtheskidder,thelogsandespe-ciallythelogheadsmighthaverippedandloosenedupthesurfaceofthehighlycompacteddownslopewheeltrack(Jamshidietal.2008).However,GayosoandIroume(1991)statedthatthismaybeaconse-quenceof theproblemthat theskiddermight facewhenlogginginsteepterrains.Undertheseconditions

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thevehicleslippedcontinuouslyandremainedinagivenplaceforalongerperiodoftime,puddlinganddragging the soil. In uphill skidding, rubber tiresslippedonsurfacesoil,thenthiswheelslippage,thevibrationappliedandshearstrengthcausedtheexpo-sureofmineralsubsoil,whichhashigherdensitythansurfacelayer.Also,highersoilcompactionintheup-hillskiddingcanbeexplainedbythehigherloadoftheskidderrearaxle.Intheotherhand,uphillskid-dingresultedinseverdisturbanceandcompactionininitialvehiclepass,howeverbulkdensityinthiscondi-tionhadthehighestamountincomparisontodown-hillskiddingandflatskidtrail.Also,Jamshidietal.(2008)foundthattherewasnodetectabledifferenceincompactionbetweenvehicleskiddingonflattrailsandtrailswithlongitudinalgradientortransversalslope.Theyconcludedthatthedifferentsiteconditionsandskiddingfrequenciesmighthaveaffectedtheimpactsofthedifferentgradients/slopes.

4.3Soilcompaction:influenceofslopesandsoildepths – Zbijanje tla: utjecaj nagiba terena i dubine tlaTheresultsshowedthataveragepre-harvestbulk

densities significantly increased as soil depth in-creasedforallslopegradients.Thewheelortrackslipdirectlyaffectedthesoilstructureandalteredphysicalsoilpropertiesdowntodeeperdepths.Intheotherhand, the values of the undisturbed soil bulk density mostlydependsonthequantityoforganicmatter,andincreasingsoildepth;theorganicmatterrapidlyde-creases,andthebulkdensityincreasesinsubsoil.Intheuppersoil,biologicalactivity(rootsandanimals)can act to reduce resistance and soil bulk density while atlowerdepthssoiltexture,gravelcontentandstruc-turemayincreasesoilresistanceandsoilbulkdensity(GreacenandSands1980;AdamsandFroehlich1984;Froese2004;Johnsonetal.2007).Inthisstudy,withincreasing soildepth the compaction level also in-creased,which is in agreementwith the results ofotherresearchers(GreacenandSands1980;SidleandDrlica1981;GentandMorris1986;GayosoandIroume1991;Aresetal.2005;EliassonandWasterlund2007;Johnsonetal.2007).Theresultsshowthatdeeperinthesoilprofile,differencesbetweencontrolandthetreatmentsinfourslopegradientbecamesmaller.Thehighest level of increase in bulk density was found in thetrailwith10%slopegradient(uphill)betweencon-trolandthetreatments.Inflattrail,bulkdensityin-creasedsignificantlyinalldepths.Thisisrelatedtotheratherhomogeneousweightdistributionoftheskid-deronflatskidtrails.Compactioneffectismostdis-tinctintheupper20cmofthesoil,sincetheexertedpressureismaximalatthesoilsurfaceanddeclines

withincreasingdepthasthetotalpressureisspreadoutoveranenlargingarea.Thus,anincreasegener-allyoccursespeciallyintheuppersoillayers(GreacenandSands1980).Itcouldalsobesuggestedthatthebearingcapacityofthesoil(maximumloadwithoutsoilstructurefailure)growswithincreasingbulkden-sity.Inthiswaythesurfacelayerisprotectedagainstfurthercompactionwhentraffic iscontinued(Am-poorteretal.2007).

5. Conclusion – ZaključakAccordingtoourfindings, itmaybeconcluded

thatthehighestrateofcompactionoccurredaftertheinitialfewpassesandreducingthenumberoftripsmadeoverthesametrailhadnoeffectinreducingsoilcompaction. In theotherhand, subsequentvehiclepasseswillresultindiminishingextrasoilcompaction.Hence,evenonepassisalreadysufficienttoinduceastrongincreaseinbulkdensity.So,skiddingopera-tionsshouldbelimitedtopre-plannedskidtrails,be-causevehicletrafficawayfromskidtrailscansignifi-cantlyaffecttheincreasingofthesoilbulkdensity.Theresultsofthisresearchconfirmedthatpreplanningofskid trails and directional felling will reduce ground disturbance.Slopegradienthasasignificanteffectonsoilcompaction.Basedontheresults,itcanbecon-cludedthatuphillslopegradientsontrailsshouldbeaslowaspossible,particularlywhenvehiclesaretrav-eling loaded.The studyshowed that the skid trailslopeandvehiclepasseshadasignificanteffectonsoilcompaction.Severecompactionofsoiladverselyaf-fectsthegrowthofplantsbyacombinationofphysicalsoil changesandplantphysiologicaldysfunctions.Skiddingoperationsshouldbeplannedwhensoilcon-ditionsaredrysoastominimizesoilcompaction,butifskiddingmustbedoneunderwetconditions,theoperationsshouldbestoppedwhenthevehicletrafficcreatesseversoilcompaction.Thedistancebetweenthesetrailsmustdependonthelengthofthefelledtreeandmayrangebetween50and70mdistanceinordertoreducethewinchingdistance.Theimpactoffellingoflargetreesisanothersourceofcompactionbutthisaspecthasnotbeenstudiedinthisresearch.

Acknowledgements – ZahvalaThispaperisoneoftheresultsofaresearchproject

thatwascarriedoutintheperiod2010–2012intheHyrcanianforestinnorthernIran.TheauthorswouldliketoacknowledgethefinancialsupportofIranianNationalScienceFoundation(INSF)fortheresearchprojectNo.88001084.

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Sažetak

Utjecaj broja prolazaka kotačnoga skidera na zbijanje tla

Upotreba je kotačnih skidera vrlo česta za privlačenje drva iz šume, ali pritom vozilo negativno utječe na okoliš. Cilj je istraživanja bio ispitati kako različiti nagibi terena (odnosno traktorskih vlaka), broj prolazaka vozila po trak-torskoj vlaci i dubina tla utječu na zbijanje tla. Istraživano je zbijanje tla na četiri nagiba traktorskih vlaka: ravan teren, nagibi od +10 %, -10 %, -20 %; na tri različite dubine tla: 5, 15 i 25 cm te s obzirom na broj prolazaka vozla po vlaci: 0, 1, 5, 8, 10, 15, 20, 25 i 30 (slika 7). Uzorci su tla uzimani unutar traktorske vlake i izvan nje (slika 4) svakih 25 m duž vlake kako bi se vidio utjecaj natovarenoga vozila na tlo. Istraživanje je provedeno u Nastavno-po-kusnom šumskom objektu Kheyrud, koji se nalazi unutar Hirkanijske šume u sjevernom Iranu, a drvo je privučeno skiderom Timberjack. Traktorske su vlake zauzimale 5,8 % ukupne površine istraživanoga područja (17 ha) uz do-datnih 0,8 % površine potrebne za pomoćno stovarište. S povećanjem broja prolazaka vozila povećala se i gustoća tla, ali je ipak najveće zbijanje tla ustanovljeno u prvih nekoliko prolazaka vozila. Privlačenje drva uzbrdo (+10 % nagi-ba terena) više je zbijalo tlo (slike 5 i 6) nego privlačenje drva nizbrdo (nagibi terena -10 % i -20 %). Povećanje je gustoće tla i na dubini od 20 do 30 cm bilo značajno (slika 8). Gustoća je tla na dubini od 5, 15 i 25 cm bila veća za 35, 22 i 17 % od gustoće tla na netaknutom tlu (slika 9). Kako bi se smanjilo zbijanje tla, potrebno je privlačiti drvo po unaprijed planiranim i za to predviđenim traktorskim vlakama te usmjereno obarati stabla kako bi se smanjilo kretanje vozila po šumskom bespuću jer već i nakon prvoga prolaska vozila dolazi do povećanja gustoće tla i njegova zbijanja. Također, privlačenje se drva treba odvijati u uvjetima suhoga tla kako bi se smanjila oštećenja na šumskom tlu.

Ključne riječi: zbijanje tla, gustoća tla, kotačni skider, Hirkanijske šume

Received(Primljeno):February12,2012Accepted(Prihvaćeno):Jaqnuary11,2013

Authors’address–Adresa autorâ:

Prof.BarisMajnounian,PhD.e-mail:[email protected],PhD.*e-mail:mjgholami@ut.ac.irUniversityofTehranFacultyofNaturalResourcesDepartmentofForestryandForestEconomicsP.O.Box:31585–431KarajIRAN*Correspondingauthor–Glavni autor