John D. Williams, Department of Rangeland Resources, Oregon ... installed and monitored for 2 winters and 1 summer to determine if runoff and erosion ...
Winter Logging and Erosion in a Ponderosa
Pine Forest
in
Northeastern Oregon John D. Williams, Departmentof RangelandResources,Oregon StateUniversity,Corvallis,OR 97331 and John C. Buckhouse, Departmentof RangelandResources,OregonStateUniversity, Corvallis, OR 97331.
ABSTRACT. Treesare oftenharvestedin smallwoodlotsfor the dual purposeof generatingrevenueand expandingor enhancingwoodlandpasture for livestockand wildlife.Followingsuchan effort,in a two-part studywe comparedtherunoffand erosionpotentialin harvestedand nonharvested sites.The treeharvestwas conducted onsnowandfrozensoilandusedprescribedskidtrails.Inthefirst part of thestudy,runoffplotswere installedand monitoredfor 2 wintersand 1 summerto determineif runoffand erosionresultingfrom natural precipitationeventsoccurred from eitheroftwotreatments; a harvested siteor a comparable nonharvested site. In thesecondpart of thestudy,simulatedrainfall wasappliedto a separatesetof runoffplotsto determine endpointinfiltrationcapacityand to makeprojectionsof infiltrationand erosionresponseto anticipated livestockgrazing.Rainfall wasappliedto eachplot at threesubsequent levelsof groundcovermanipulation: undisturbedvegetation,clippedvegetation,and vegetationand organicsoil horizon removed. No runoff or sedimentproductionwas recordedbetweenSeptember1986 and December 1987 in either harvestedor nonharvested treatments in theplotsmonitoringresponse to naturalrainfall.In addition,runoffandsediment productiondidnotoccurasa resultof simulatedrainfallin eithersiteregardless of thegroundcovertreatment. The sameresultwas obtainedwhenrainfall was appliedfor an extendedperiod and at an increasedrate of application.Thelackof runoffcanbeattributedto siteconditions,especiallythewell-developed biomassin the uppersoilhorizons,andthemethodandseasonoflogging.lf thetreeharvestprocedures are repeatedin similar sites,similarresultsmaybe expected.West.J. Appl.For. 8(1): 19-23.
Theeffects oflogging onthehydrology andsoilstability of
Heede (1984, 1987) in Colorado and Arizona. Similar re-
a forestedwatershedcan be numerous.Road building, tree
searchhas not beenreportedin the literaturefor ponderosa pineforestsof the northwestern UnitedStates. Simulatedrainfall studieshavebeenconductedon many rangelandsof the western United States (Thurow 1991). However,few suchstudieshavebeenconducted in theponderosapine forestsof the Northwest.Buckhouseand Gaither (1982) and Gaither and Buckhouse(1983) testedpotential sedimentproduction andinfiltrationratesin a ponderosa pine forestin northeastern Oregon.However,theirresearchdidnot examinehydrologicresponse to purposefulmanipulationof thesesystems,e.g., the disturbanceof litter and understory
falling and removal,and slashburningcompactthe soil, removeprotectivecover,andcanleadto accelerated erosion (Dymess1965). Surfaceflow anderosionon skidtrailsoften resultfrom removalof groundcoverby loggingon thedeep permeablesoilsof northeastern Oregon(Helvey andFowler 1979). The soil lossfrom runoff on skid trails can be great;
Heede (1960)reported 6.36m3of soilwashed froma 277m long skid trail in the year following harvest.Revegetation alonemaynotbeenoughto preventthisproblem(Helvey and Fowler 1979). There have been few small plot studiesof runoff and erosionresultingfrom naturalprecipitation eventsin ponderosapineforests.The onlysimilarresearch wasconducted by NOTE: Submitted asTechnicalPaperNo.9691,OregonAgricultural Experiment Station,Corvallis.The authorsgratefullyacknowledgesupportand fundingfromtheEasternOregonAgriculturalResearch Center,Bumsand Union,Oregon.JohnD. Williamsis currentlyGraduateResearchAssistant, Departmentof RangeScience,Utah StateUniversity,Logan,Utah 843225230.
growth. The methodandseasonof harvestandtheresultingdisturbance are crucial considerations for soil and water conserva-
tion.Loggingonsnowandfrozensoilis onepossiblemethod of reducingthe impactof the harvest.The objectiveof this studywasto determinewhetherrunoffandsedimentproduction from natural rainfall events or simulated rainfall differed
between harvested (on snow-covered frozen soil) and nonharvested sites.
WJAF 8 (1) 1993 19
Methods
ceptedfor computedChi-squaredanalysis(Steeland Torrie 1980).
Descriptionof Study Site The studywasconductedon the Hall Ranch,a part of the EasternOregonAgriculturalResearchCenter(EOARC) at Union, Oregonin the southwestern foothillsof the Wallowa Mountains(43ø12'N, 117ø53'W). The elevationat the site is 1060 m.
The climateis a dry midlatitudesemi-aridclimategroup controlledby tropicalmassesproducingwesterlywindswith polar air massescreatingoccasionalpolar winds.Basedon monthlymaximumandminimumrecordsfrom 1963to 1987, the averageannualair temperatureat the researchsite was 7.7øC;for 3 monthsof theyearthemeantemperature isbelow freezingandonlyJulyis typicallyfrost-free.Annualpotential evaporationrangesfrom 650 mm to 700 mm (Strahlerand Strahler1983). Stormsmaybe eitherconvectionalor frontal.
Theaverageannualprecipitation from 1963to 1987was600 mm. Snow depthaverages230 mm from Octoberthrough March. A weather station was located within 50 m of the
researchsite and consistedof recordingand standardrain gaugesandmaximum/minimum thermometers. The recordinggaugemeasured 6-hrintensities. In addition,standard rain gaugeswereplacedat eachplot. The largeststormrecordedin the last40 yr at the Union
meteorological station was26mmh-1.Theestimated return period forthenextlargest storm, 19mmh-1is13to20yr.The maximumprecipitationrate at the researchsite duringthe
study period was17mm6h-1fromatotal of1206-hrperiods of precipitation.The largest6-hr accumulationduringthe sameperiodat EOARC was9 mm. The study was conductedin a ponderosapine (Pinus ponderosa)/snowberry (Symphoricarpos albus)plant communitytypecommonin northeastern Oregon,easternWashington,and adjacentportionsof Idaho (Riegel 1992). Two siteswereharvestedafterwhichtreedensityaveraged1 stem
per68 m2 (Site1) andonestemper132m2 (Site2). In both sites,treeswereselectivelyremovedby rubbertired skidders usingpredetermined skid trails duringthe winter of 1986 while snowcoveredthegroundandsoilswerefrozen.Before removal,thetreeswerelimbedandcutto commercialsaw-log length; all limbs were left on site and the tree tops were removedandpiled outsideof the treatmentarea.Smaller, excesstreeswerefelled in July andAugust1986 andleft in place. The following sitecharacteristics weremeasuredwithin eachloggingtreatment;meansfor precipitation persediment collectionperiod,total accumulated precipitation,slope,aspect,groundcover(Daubenmire1959),canopycover(Jones and Campbell1979), potentialsolarradiation(Chan et al. 1986), the depthof the organicsoil horizon,bulk density (BlakeandHartge1986),andpenetrometer ratings(Davidson 1965).A one-wayANOVA wasusedto testfor differences
The soil within the studysiteis a Tolo series(medialover loamy,mixed,frigidTypicVitrandepts)andoccurson2% to 35% slopes.It is a well-drainedsoil,andtheaverageavailable water holdingcapacityis 320 mm (Dyksterhuisand High 1985).
ExperimentalDesign Borderedrunoff plots (Williams and Buckhouse1991) were installedin August 1986. At this time, no evidenceof harvest(e.g., tracks,trails,or otherwisedisturbedsoil), remained from the previouswinter's harvestactivities.Plots werepositionedto excludeslashpiles,rockoutcroppings, and trees.All plotconstruction trafficwasoutsideof theplots.Plot border installation disturbance was limited to 10 mm within
eachplot dueto borderinstallation.The plotswere 1 x 5 m, with a collectiontroughat the bottomwhich carriedrunoff into a collection bucket. Had runoff occurred,it would have
been measuredusing a 1000 ml graduatedcylinder and subsequently filteredto determinesedimentproduction.Hypotheseswere designedto testfor differencesin runoff and sedimentproductionbetweenharvestedand nonharvested sitesand differentlevelsof understorydisturbance(undisturbed,clipped,andorganicsoilhorizonremoved). Hydrologicanderosionresponses to naturalprecipitation weremeasuredin 30 plotswith similarslope(20 + 3%) and aspect;half of which were locatedin Site 1 and adjacent nonharvested site,respectively.Collectionbucketswereexaminedfor accumulatedrunoff monthly from September 1986throughMay 1987,aftereverystormfromJunethrough September,andonceagainmonthlythroughDecember1987 Simulatedrainfall was appliedto 12 plots with similar slope(30 + 2%) and aspect;6 eachin Site 2 and adjacent nonharvested site,respectively. Threeinfiltrometerrunswere madeontoeachplot in a sequence of groundcoverdisturbances:(1) undisturbed understory vegetation,(2) understory vegetation onall plotsclippedto a 25 mm stubbleheightand theclippingsremoved,and(3) remainingvegetationandthe organichorizonwereremovedby shovelandall loosebiomassremovedfromtheplotsleavingbaremineralsoil.Rainfall was simulatedfor 28 min. on eachplot usingan overhead sprinklersystemconsistingof threesprinklerheadsdistributingwaterin arectangular patternwithanaveragedeliveryrate
of29mmhr-l.Rainfall intensity wasmeasured byraingauges at eightplaceswithineachplot. Ten dayselapsedbetween eachinfiltrometerrun to allow the soil profile to drain. The plots were coveredwith plastic for that period to prevent uncontrolledwetting and possibleunrecordedsurfaceflow andsedimentproduction.Infiltration runswereinitiatedonto dry soil to duplicateconditionswhich occurwith the first stormin fall followinga summerdry period. Results
between sites for each of the above characteristics with the
exceptionof coverclassdatawhichweretestedusinga Chisquaredstatistic.Fisher'stwo-tailexacttestwasusedto test cover classdata where expectedfrequencieswere not ac-
20 WJAF 8 (1) 1993
Observationsof 41 plots to measurerunoff and erosion resultingfrom naturalprecipitationor simulatedrainfallwere recorded.No runoff or erosionwere observedat any time
Table 1. Tests for difference
between means of site
characteristicsin natural precipitationplotsmeans. Means
Characteristic
Harvested
Difference
Nonharvested
between means
Precipitation(mm) Canopycover(%) Slope(%) Aspect(ø) Groundcover(%)
370 39 21 101.7 99
305 61 21 99.3 99
Yes* Yes* No* No* No*
36
71
Yes
Organichorizon(mm) Potentialsolar(x)
Discussion
There was no ranoff or sedimentproductionon either
Yes
harvested or nonharvested sites. Because this outcome is
1.07 0.73
0.96 0.90
No* No*
contraryto our expectations,we will now examinethe site conditionsand why they are conduciveto high infiltration capacitiesacrossall sites.
No*
Nonharvested
Yes 0.11
0.06
Yes
(Kgcm-2)
Hortonianrunoff will occuronly whenthe rainfallrate exceedsthe infiltrationcapacityof the soil. Gaither and Buckhouse (1983) reporteda potentialinfiltrationrateof 60
mmhr-l in a similar ponderosa pineforestin northeastern
* indicates significant differencebetweentreatment variances, thus conclusion maynotbevalidP < 0.05.
Units: millimeters (mm), kilograms perhectare (kgha-1),percent (%), degree(ø),probabilityof diffuseradiation(x), gramspercubiccentimeter
(gcm•3), and kilograms percentimeter squared.
depthof organichorizon,andpotentialdiffusesolarradiation were significantly different between harvested and nonharvested sitescontaining thenaturalprecipitation plots. Althoughtherewasnot a significantdifferencein soilbulk densitybetweensites,there was a significantdifference betweentheupperandlowerhorizonswithinthenonharvested site(Table 1). Chi squareanalysisof vegetationdatashowed thatcurrentyearsforb andgramminoid growthandthe forb component varied between the harvested site and the nonharvested sitein whichthenaturalprecipitation plotswere Table 2. Tests for difference between means of site
characteristicsin simulatedrainfall plots. Means Harvested Nonharvested
Oregon.The rateof naturalprecipitationat the researchsite duringthestudyperioddidnotreachthehistoricalmaximum rate recordedat the nearbyUnion meteorological station. Evenif therainfallintensityattheresearch siteweretwicethat
ofthe40yr maximum recorded atUnion(--52mmh-l),it is
duringthe studyin eitherharvesttreatment(Site 1 or Site2) or corresponding nonharvested plots. Becausemeasurable runoffor sedimentproductionwasnot recorded,statistical analysiswasnotrequired. Precipitation(to reachthe forestfloor), canopycover,
Characteristic
There were no significantdifferencesbetweenthe measuredcharacteristics of the sitescontainingthe simulated rainfallplots(Table2).
0.40
Harvested 100 mm vs 450 mm 100 mm vs 450 mm Penetrometer
harvested site.
0.64
Bulk density (gcm © 100 mm depth 450 mm depth
located.An examination of theoriginaldata(Williams 1988) indicatethe growthandforb componentweregreaterin the
Difference between means
doubtfulthatit wouldexceedtheinfiltrationcapacityateither of the harvestedor nonharvestedsites.In addition,the simu-
latedrainfallin this researchdid not approachthe potential
infiltration capacity. Itranged from20to47mmh-1across the plots and averaged 29mmh-1,roughly 14mmper28min. run. However,this wasin excessof the 40-yr maximumstorm intensities (26 mmh-1),whichgivessomeindication whatthe response to a largenaturaleventmighthavebeen. Ground cover, live and dead biomass, and rocks that
protectmineralsoilfromdirectimpactof raindrops hasbeen citedin numerous studies asoneof themostimportant factors controllinginfiltrationcapacitiesandrunoff(Thurow1991). Groundcoverin thisstudyrangedfrom77%to 100%withan averageof 98%. At all sitesbaregroundwasthe resultof rodentactivity.If soilhadbeenexposedby theharvestduring the winter of 1985-86, it had overgrownby June 1986. Furthermore, understory vegetation onall siteswascomposed of greater than50%gramminoid species resulting in a subsurfacesoilhorizonwitha well-developed fibrousrootcomponentin variousdegrees of decomposition. Manyofthegrasses and forbs found at the site are rhizomatous and contribute to
Slope(%) Groundcover(%) Organichorizon(mm)
30 96 48
30 99 67
No No* No*
Bulk density (gcm -3) 100mm depth 450 mm depth
0.95 0.94
0.89 0.93
Harvested 100
No No* No*
mm vs 450 mm
Nonharvested 100 mm vs 450 mm Penetrometer
No 0.26
0.27
No
(Kgcm-2) * indicates significant difference between treatment variances, thus conclusionmaynot be valid P < 0.05.
Units: millimeters (mm), kilograms perhectare (kgha-1),percent (%), degree (ø),grams percubic centimeter (gcm -3),and kilograms per centimetersquared.
infiltrationandsoilstabilization byreducing raindrop impact. Because of thenearcomplete coverandintactbelowground biomass, thesurface wasprotected fromraindrop impact,and the soil structure wasretainedthusmaintaining conditions necessary for highinfiltrationrates. Thedepthof theorganichorizonplaysanimportant rolein infiltrationcapacityby maintaininga porousinterfacebetweenthe atmosphere andmineralsoil.Betweenthe natural precipitationplots,the organichorizonin the nonharvested sitewassignificantlydeeperthanin theharvestedsite.However,thishadno apparent effectontheinfiltrationcapacity, becauseall precipitation notevaporated from plantandsoil surfaces infiltrated intoall sites.Theorganichorizonwaswell developed inbothsitescontaining thesimulated rainfallplots, WJAF 8 (1) 1993 21
averagingabout55 mm.Thislayeralonehadthepotentialfor absorbing20 mm of rainfall (Clary andFfolliott 1969). There were no differencesin bulk densitybetweenharvestedor nonharvested sitesfor eithersetof plots.Increased
capacityof thesitebyincreasing therateof application across an entireplot. A singlerun wasmadethatcontinueduntil the
bulk densityresultsfrom activitiesthat break down the soil structure,crushingpore space,which in turn can lead to
min., no surfaceflow wasproducedoutsideof the localized flow in theupperrighthandcomerof theplot. Thislackof measured surfaceflow andsediment production atteststo the residualsoilstructure andwell-developed rootmassin thesoil profile.
decreasedinfiltrationcapacity.Bulk densitytypically increaseswith soildepth.Thiswasthecasein thenonharvested sitein which the naturalprecipitationplotswere locatedand in bothsitesof simulatedrainfallplots.However,therewasno differencebetweenbulk densityat the two depthsin the harvestedsite in which the naturalprecipitationplots were located.This may indicatean increasein bulk densityin the upperpart of the profile, apparentlythe resultof harvest activities.There was a large variationin the data from the harvestedsitewhichmay be attributedto serendipitous location of a numberof plotson skidtrailsor wheretreesfell. As notedpreviously,by the time positionsfor the plots were chosen,all signsof theseactivities,suchas bermsfrom soil displacement,were gone.But sincethere was no runoff in eithersetof plots,the degreeto whichbulk densitymayhave beenincreasedappearsnottohavebeendeleterious to infiltration capacities.This supportsthe contentionof Sniderand Miller (1985) that loggingdoesnot alwaysseverelyalter a site.Generally,the soilhad a low bulk densityandwas well drained, which is characteristicof the Tolo soil series.
The surprisingoutcomewas that after all vegetationand looseorganicmaterial was removedand simulatedrainfall appliedto baresoil,no surfaceflow occurred.Rainfall strik~ lng a baresoilsurfaceis generallyacknowledged to dislodge soil particles,creatingsplasherosionwhich plugs the soil poresand eventuallyleadsto surfaceflow. When not protectedby a vegetativecover,theTolo soilseriesisproneto rill and gully erosion(Dyksterhuisand High 1985). The lack of runoff anderosionmay be explainedby the minimal disturbanceto the soil structure.With only the vegetationand organichorizonremoved,and assumingthat the site originallyhad a potentialinfiltrationcapacityof 60
mm hr-1, thentheconditions of soilstructure, textureand antecedent moisturemay stillhavebeenadequateto maintain a higherrateof infiltrationthanthe naturalor appliedrateof rainfall. A secondexplanationis thatthe sizeandvelocityof the simulatedraindropswere not great enoughto have the kineticenergyrequiredto dislodgesoilparticles.Thusinfiltrationwouldhavecontinuedto becontrolledby soilstructure and antecedentsoil moisture.Finally, it is doubtfulthat the soil profile approachedsaturationin eithernaturalor simulated parts of this studybecausethe Tolo seriesis a welldrainedsoil,andthepotentialevapotranspiration of thisarea exceedsprecipitation.In thenaturalprecipitationplots,runoff mighthaveoccurredwith a rainon snowandfrozensoilevent. This, however,did not occurduringthe periodof study. The likelihood that surface flow would have occurred if the
watersupplywas exhausted.A total of 84 mm of rainfall was
applied atanaverage rateof39mmhr~1.After2 hrand10
Conclusion
No runoff or sedimentproductionwas observedunder eitherharvested (onsnowcover,frozensoils,anddesignated skidtrails)or nonharvested conditions resultingfrom either naturalprecipitationor simulatedrainfall. Furthermore,no runoff or sediment resulted from simulated rainfall from
either harvestedor nonharvested plots subjectedto three differentlevelsof groundcoverdisturbance the first year followingharvestonthisnortheastern Oregonponderosa pine site.
Theseresultsaresimilarto thoseof Hart (1984), whereless than 1% of the simulated rainfall became runoff. We believe these results are due to the harvest method and the weather
conditionsduringthe studyperiod. Thiseffortsupports previousfindingsthatrunoffin undisturbedforestedsystemsis rare and shouldnot occurwhere loggingsystemscreateminimalon-sitedisturbance (Heede 1987).Thesefindingsshowtheimportance of well-planned tree harvestto preservebelowgroundroot structureand or-
ganicmatteras well as soil structurein the initial year followingharvest. If timberharvests invegetation community typeswith similarsiteconditions aremodeledaftertheloggingpractices(on snowcover,frozensoils,andprescribed skidtrails)usedin this study,thechancesfor runoff and soil erosionin the year following harvestwill be diminished. Finally, the lack of runoff from the clippedplotssuggests livestockgrazingthatdoesnotsignificantly compactthesoil or createextensivebareareasmaybepossiblewithoutsevere erosion risk.
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WJAF 8 (1) 1993 23
