Chemical Changes Induced by pH Manipulations of Volcanic ... · Chemical Changes Induced by pH Manipulations of Volcanic Ash-Influenced Soils Page-Dumroese, Ferguson, McDaniel, and

1��USDA Forest Service Proceedings RMRS-P-44. 2007

In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. Volcanic-Ash-Derived Forest Soils of the Inland Northwest: Properties and Implications for Management and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.

Deborah Page-Dumroese and Dennis Ferguson are Research Scientists at the Rocky Mountain Research Station, U.S. Forest Service in Moscow, ID; Paul McDaniel and Jodi Johnson-Maynard are faculty in the Department of Plant, Soil, and Entomological Sciences, University of Idaho, Moscow, ID.

Abstract Datafromvolcanicash-influencedsoilsindicatesthatsoilpHmaychangebyasmuchas3unitsdur-ingayear.Theeffectsofthesechangesonsoilchemicalpropertiesarenotwellunderstood.OurstudyexaminedsoilchemicalchangesafterartificiallyalteringsoilpHofash-influencedsoilsinalaboratory.Soilfromthesurface(0-5cm)andsubsurface(10-15cm)mineralhorizonswerecollectedfromtwoNationalForestsinnorthernIdaho.Soilcollectionsweremadefromtwoundisturbedforeststands,apartialcut,anaturalbrackenfern(Pteridium aquilinum[L.]Kuhn)glade,anapproximately30-year-oldclearcutinvadedwithbrackenfern,anda21-year-oldclearcutinvadedwithwesternconeflower(Rudbeckia occidentalisNutt.).Eitherelementalsulfur(S)orcalciumhydroxide(Ca(OH)2)wereaddedtothesoiltomanipulatepH.After90daysofincubation,pHrangedfrom3.6to6.1forbothNationalForestsandallstandconditions.TotalC,totalN,andextractablebasecations(Ca,Mg,andK)weregenerallyunaffectedbypHchange.AvailablePincreasedaspHdroppedbelow4.5forbothdepthsandallsoiltypes.NitratewashighestatpHvaluesgreaterthan5.0anddecreasedaspHdecreasedindicatingthatnitrificationisinhibitedatlowerpH.Contrarytonitrate,potentiallymineralizableNincreasedaspHdeclined.TotalacidityandexchangeablealuminumincreasedexponentiallyaspHdecreased,especially intheuncutandpartialcutstands. Datafromthis laboratorystudyprovidesinformationontheroleofpHindeterminingtheavailabilityofnutrientsinash-capsoils.

Chemical Changes Induced by pH Manipulations of Volcanic

Ash-Influenced SoilsDeborah Page-Dumroese, Dennis Ferguson, Paul McDaniel, and

Jodi Johnson-Maynard

Introduction

Innorth-centralIdaho,someforestsarecharacterizedbyconiferregenerationproblemsdespitefavorableclimaticconditions(udicmoistureandfrigidsoiltemperatureregimes).Foreststandsatmid-elevationsaremostatriskaftertimberharvestorotherdisturbancebecausetheyarequicklyinvadedbybrackenfern(Pteridium aquilinum[L.]Kuhn),westernconeflower(Rudbeckia occidentalisNutt.),andpocketgophers(Thomomys talpoides).ThesesitesarecollectivelyknownastheGrandFirMosaic(GFM)andarenamedforthedominantconifer,grandfir(Abies grandis[Dougl.exD.Don]Lindl.),thatoccursinamosaicpatternwithshrubandforbcommunities(Ferguson1991a;Fergusonandothers,thisproceedings).

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Page-Dumroese, Ferguson, McDaniel, and Johnson-Maynard Chemical Changes Induced by pH Manipulations of Volcanic Ash-Influenced Soils

TimberharvestingbeganintheGFMinthe1960sanditsoonbecameevidentthatregenerationproblemsexisted.Woodyvegetationisstillinfrequentonmanyofthesesites30yearsafterclearcutting,evenwithrepeatedplantings(FergusonandAdams1994).Clearcutstandswerequicklyinvadedbyforbs(predominatelybrackenfernandwesternconeflower)androdents.Theallelopathicpotentialofbothbrackenfernandwesternconeflowerhasbeenwelldocumented(Stewart1975;FergusonandBoyd1988;Ferguson1991b).Inadditiontoinvadingforbs,pocketgophersalsocausesubstantialseedlingmortality (Fergusonandothers2005).Competition for light,moisture, andnutrientswithin theGFM ishigh.Whilethecombinationofcompetition,pocketgophers,andallelopathycontributetothearrestedstateofsecondarysuccession(FergusonandAdams1994),thesefactorsdonotappeartoentirelyexplainreforestationfailures.

Soils throughout the GFM are strongly influenced by volcanic ash in thesurfacehorizons.Theashwasdepositedapproximately7,700yearsagowhenMt.Mazama erupted (Zdanowicz 1999). Volcanic ash-influenced soils haveuniqueparentmaterialsandsecondarymineralassemblagesthat,ingeneral,arenotaswellunderstoodasthoseinothermineralsoils.Volcanicash-influencedsoilsareclassifiedaseitherallophanicornonallophanic,dependingontherela-tiveabundanceoforganicmatterandinorganicshort-range-orderminerals(Shojiand others 1993). Nonallophanic soils have more organic matter, lower pH,higherlevelsofKCl-extractablealuminum(Al),andlowerlevelsofcalcium(Ca)relative toallophanicsoils (Shojiandothers1993).LowsoilpHmay increaseconcentrationsofextractable(potentiallyplantavailable)Al,leadingtoAltoxic-itytowoodyvegetation(Dahlgrenandothers1991).Clearcuttingandintensiveutilization(wholetreeharvesting)offorestbiomassmayacceleratesoilacidifica-tionprocesses(Ulrichandothers1980;NoskoandKershaw1992).Inadditiontoacidificationfromharvestactivities,vegetation-inducedacidificationappearstooccurunderbrackenfernandwesternconeflowerplantcommunities(Johnson-Maynardandothers1997).Theseacidifiedvolcanicash-influencedsoils,whicharehighinexchangeableAl,mayreleaseAlintosoilsolutionatlevelstoxictowoodyvegetation(AndereggandNaylor1988).

Twosoil factorshavebecomeaconcerninGFMforestopenings.First,soilpH drops below 5.0 after harvest operations and the subsequent invasion ofbrackenfernandwesternconeflower(figs.1and2).AtthispH,AlcanreachtoxiclevelsandlowsoilpHcaninhibitgrowthofsomeseedlingspecies(NoskoandKershaw1992).Second,thereareseasonalpHfluctuationsof2-3pHunitsthatarenottypicallyfoundinbulkmineralsoilunlessheavilyimpactedbyacidrainor,occasionally,harvestactivities(Mrozandothers1985;Braisandothers1995;Alewellandothers1997).WinterpHvaluesaveragearound6,butdropbelow4duringthegrowingseason.TheseseasonalpHfluxescouldbecorrelatedwithinputsofacidlitterfrombrackenfernandwesternconeflower,increasingrootrespirationduringthegrowingseason,ordecreasesinsoilmoisturecontent.Inaddition,thesetwospecieslikelytakeuphighamountsofnutrientsfromthesoil,whichmayalsocontributetoacidconditions(Gilliam1991).ManyfactorsinfluenceforestsoilpH(forexample,precipitation,nutrientexchange,andsoilage),butharvestactivitycanparticularlyinfluenceit (StaafandOlsson1991).AlthoughforestharvestingcanlowerpH,subsequentinvasionbybrackenfernandwesternconeflowerappearstocontributetoandmaintainlowpHrelativetoundisturbedforestsoils.

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Chemical Changes Induced by pH Manipulations of Volcanic Ash-Influenced Soils Page-Dumroese, Ferguson, McDaniel, and Johnson-Maynard

Figure 2—Average soil pH at 2.� cm for the Clearwater National Forest fern-invaded clearcut (unpublished data collected as described in Ferguson and Byrne 2000). The bold line is 1997 and the thin line is 199�.

Figure 1—Average soil pH at 2.� cm for the Nez Perce National Forest coneflower-invaded clearcut (from Ferguson and Byrne 2000). The bold line is 1994, which was a dry growing season. The thin line is 199�, which was a wet growing season. Dis-continuous parts of the line are from removal of the pH probe during the driest part of the growing season. Soil pH at this site was assessed in situ using pH probes (model �1�, IC controls Orangeville, Ontario, Canada) buried 2.� cm below the mineral soil surface.

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TheslowforestregenerationprocessintheGFMhasdecreasedmanagementoptionsforfuelreductionsandbiomassproduction,biodiversityofnativefloraandfauna,andaestheticvaluesinandneartheseareas.LowsoilpHanditscyclicnatureover a growing seasonmaybealtering soil chemistry, nutrient cyclingprocesses, and preventing establishment of woody vegetation. Consequently,ourobjectivewastoartificiallyalterpHofash-influencedforestsoilsfromtheGFMbyadditionsofsulfur(S)orcalciumhydroxide(Ca(OH)2)tobetterevaluatepotentialin situ chemicalchangeswithinthesesoils.

Study Site Description ___________________________________________Twostudysites,oneontheClearwaterNationalForestandoneontheNez

PerceNationalForestofnorth-centralIdaho,wereselectedtoprovideanorth/southrangeofplantcommunitycovertypesforsoilcollection.TherearethickerdepositsofvolcanicashinthenorthernpartoftheGFMwherethesesoilsareclassifiedasAndisols.InceptisolsdominateinthesouthernpartoftheGFMwhereashdepositsare thinnerandmorehighlymixed.Bracken ferndominates forbcommunitiesinthenorthernpartoftheGFMandwesternconeflowerdominatesinthesouthernpart,althoughbothspeciesoccurtogetherthroughouttheGFM.Table1listsstudysitelocations,vegetationtypes,andsoilclassifications.

ClearwaterNational Forest soil sampleswere collected in 1994near EaglePoint(elevation1,400m,easternaspect,20percentslope,T40N,R7E,S35).Thedominantsoilfeatureofthisstudyareaisapproximately60cmofMt.Mazamavolcanic ashunderlainwith colluviumor residuumderived from fine-grainedigneousrock.Toassesstheimportanceofvegetationcommunitystructure,soilsampleswerecollectedfromadjacentareaswithsimilarslope,aspect,andpar-entmaterial, butdifferent vegetationcover. Soil sampleswere collected fromtheundisturbed forest (46m2ha–1basal areaofoverstory), apartial cut (ap-proximately30m2ha–1ofoverstoryremaining),anaturallyoccurringbrackenfernglade(presentwhentheadjacentareaswereharvested),anda~30-year-oldbrackenfern-invadedclearcut(invadedbybrackenfernandwesternconeflowerafterharvestingbetween1965and1968).

NezPerceNationalForestsoilsampleswerecollectedin1994atDogleg(eleva-tion1,740m,southernaspect,5percentslope,T31N,R6E,S34).Thedominantsoilfeatureisapproximately40cmofMt.Mazamavolcanicashunderlainwithdeeplyweatheredmicaschist(Sommer1991).Vegetationtypesatthissitewereundisturbedforest(45m2ha–1basalareaofoverstory)anda21-year-oldwestern

Table 1—Location, vegetation type, and soil classification of study sites.

National Forest Vegetation type Soil classification‡

Clearwater Undisturbed forest Typic HapludandNez Perce Undisturbed forest Vitrandic CryumbreptClearwater Partial cut Typic HapludandClearwater Natural bracken fern glade Alic FulvudandClearwater �0-year-old bracken fern-invaded clearcut Alic HapludandNez Perce 21-year-old western coneflower-invaded clearcut Vitrandic Cryumbrept‡ Clearwater National Forest soil classifications from Johnson-Maynard and others (1997)Nez Perce National Forest soil classifications from Sommer (1991).

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coneflower-invadedclearcut(invadedbywesternconeflowerandbrackenfernafterharvestingin1973).Vegetationtypeswereadjacenttoeachother,havingsimilarslope,aspect,andparentmaterial.Therewerenonaturalwesternconeflowergladesdatingtopre-harvestactivitiesandnopartialcutstandsinthevicinity.

Methods _______________________________________________________

Field Collection Methods

Ineachforestandvegetationtype,mineralsoilwascollectedfromthe0-5cmand10-15cmdepths.Soilsampleswerebrought to theUSDAForestService,MoscowLaboratory,airdried,andpassedthrougha2-mmsieve.InitialpHwasmeasuredelectrometricallyina2:1water:soilsuspension.

Laboratory Methods

DependingoninitialsoilpH,wechosefivetreatmentstoraiseorlowersoilpHinanattempttoestablisharangeofpHvaluesfrom3.5to6.0.Foreachvegeta-tiontypeanddepth,Satratesof0.45,0.90,1.80,2.70,or3.6gkg–1orCa(OH)2atratesof0.45,0.90,or1.80gkg –1wereaddedtoprovidearangeofpHvalues.Inaddition,therewasacontrol(nochemicaladded)foreachvegetationtypeandsoildepth.EachSorCa(OH)2soiladditionrateandthecontrolfromeachvegetationtypewasreplicatedthreetimes.Soilwasplacedin655cm3plastictubeswithnylonscreenoverthebottomopeningstopreventsoilloss.

Soilwaterpotentialwasbroughtto–0.033MPabytheadditionofdeionizedwater.Thetubeswererandomlylocatedonagreenhousebenchandincubatedatadaytimetemperatureof25°Candanighttimetemperatureof18to20°CuntilthepHstabilized(90days).Whensoilwaterpotentialdroppedbelow–0.10MPa,additionaldeionizedwaterwasaddeduntilthesoilreachedfieldcapacity.AfterpHstabilized(unchangedfor5days),soilwasairdriedforchemicalanalyses.FinalpHwasmeasuredasdescribedaboveaftertheincubationperiod.

Totalcarbon(C)andnitrogen(N)wereanalyzedinaLECOinductionfurnaceoperatedat1050°C(LECOCorp,St.Joseph,MI).Totalacidityandexchange-ableAlwereextractedwith1NKCl (BertschandBloom1986).Exchangeablecalcium(Ca),magnesium(Mg),andpotassium(K)wereextractedusing1NNH4Cl(Palmerandothers2001).CalciumandMgwereanalyzedbyatomicabsorptionspectroscopy,andKwasanalyzedbyflameemission.Nitrate-N(NO3-N)wasdeterminedonmoistsamplesusing1NKClextractandanAlpkemRapidFlowAnalyzer(Mulvaney1996).PotentiallymineralizableN(PMN)wasestimatedus-ingthe7-dayanaerobicincubationtechniqueonmoistsamples(Powers1980).Extractablephosphorus(P)wasdeterminedusingeithertheBray1method(forsampleswithapH<6.0)ortheOlsenmethod(forsampleswithapH>6.0)(Kuo1996).Organicmatterwasdeterminedbyweightlossaftercombustionat375°Cfor16h(Ball1964).

Statistical Analyses

RegressionequationsweredevelopedusingPROCMIXEDinSAS(Littellandothers1996),atthe0.05significancelevel,andLSMEANSwasusedtocomparevegetationtypeswithinsoildepths.WhenanalyzingresultsforCa,weexcluded

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treatmentstoraisesoilpHbecausetheCa(OH)2wouldhaveartificiallyelevatedCalevels.Transformationsofvariableswereexploredtoachievehomogeneityoferrorvariance,normalityandindependenceoferrorandblockeffects,andtoobtainadditivityofeffects(Littellandothers1996).

Results and Discussion ___________________________________________

Soil pH Changes

FieldstudiesintheGFMindicatethatsubstantialpHfluxesoccurthroughouttheyear(figs.1and2)(Fergusonandothers,thisproceedings).ResultsofourcontrolledstudyconfirmourinitialobservationthatchangesinvegetationtypeinfluenceforestsoilpH(table2).BeforetreatmentwithSorCa(OH)2,the0-5cmsoilpHwaslowestinthenaturalbrackenfernglade(5.0)andfern-invadedclearcut(4.7)ontheClearwaterNationalForest,intermediateontheNezPerceNationalForestundisturbedarea(5.4)andconeflower-invadedclearcut(5.4),andhighestontheClearwaterNationalForestundisturbedforest(6.3)andpartialcut(6.4)(table2).SoilpHatthe10-15cmdepthfollowedthesametrends.AftertreatmentwithSorCa(OH)2and90daysofincubation,finalpHvaluesrangedfrom3.6to6.1(table2).MostpHchangesoccurredwithin45daysofstartingtheincubationperiod,butthelowestpHvalueswereachievedafter85days.

Interestingly,untreatedsoilsfromtheClearwaterNationalForestundisturbedandpartialcuttreatmentsexhibitedadeclineinsoilpHduringincubationinthegreenhouse.Forexample, theinitialaveragepHintheundisturbedforestwas6.3,butattheendoftheincubationperiod,thehighestpHvaluewas5.4.This“natural”decreaseintheabsenceofvegetationandbioticprocessesissimilartothepHdecreasesshowninfigures1and2.Inthesetwofigures,winterpHvaluesaveragearound6,butdropbelow4duringthegrowingseason.TheseseasonalpHfluxesmaybedrivenbyinputsofacidlitterfrombrackenfernandwesternconeflower.Inaddition,thesetwospecieslikelytakeuphighratesofnutrientsfrom

Table 2—Initial and final soil pH ranges after treatment with S or Ca(OH)2.

National Forest Vegetation type Initial pH Final pH range - - - - - -0-5 cm depth- - - - - - - -Clearwater Undisturbed forest �.� �.7 - �.4Nez Perce Undisturbed forest �.4 �.� - �.�Clearwater Partial cut �.4 �.� - �.0Clearwater Natural bracken fern glade �.0 �.7 - �.0Clearwater �0-year-old bracken fern-invaded clearcut 4.7 �.7 - �.�Nez Perce 21-year-old coneflower-invaded clearcut �.4 �.� - �.� - - - - - - 10-15 cm depth - - - - - -Clearwater Undisturbed forest �.� �.� - �.�Nez Perce Undisturbed forest �.� �.� - �.�Clearwater Partial cut �.2 �.� - �.2Clearwater Natural bracken fern glade 4.9 �.9 - �.1Clearwater �0-year-old bracken fern-invaded clearcut 4.� �.7 - �.1Nez Perce 21-year-old coneflower-invaded clearcut �.� �.� - �.1

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thesoil,whichmayalsocontributetoacidconditions(Gilliam1991).AlthoughforestharvestingcanlowerpH,subsequentinvasionbybrackenfernorwesternconeflowerappearstocontributetoandmaintainlowpHrelativetoundisturbedforestsoils.However,thelaboratorydataindicatesthatsomepHchangeswithinthesesoiltypesarepossibleevenwithoutvegetationfacilitatingthechange.

Carbon and Nitrogen

ThereweresignificantdifferencesintotalCconcentrationamongthevegetationtypes(table3).SoilCconcentrationwashighestunderthefern-invadedclearcutatbothdepths (11.27percent0-5cmdepth;10.00percent10-15cmdepth).TotalCwas lowestat the10-15cmdepthwhereconiferswerepresent (bothundisturbedforestsandpartialcut).Thesoilsthatsupportthehighestvegetationturnoverrates(brackenfernandwesternconeflower)hadsimilarCconcentrationsatbothdepths,whilevegetationtypeswithconiferspresenthadabouttwiceasmuchCinthesurfacesoilcomparedtothe10-15cmdepth.

Thefern-invadedclearcuthasapproximately390g/m2ofbrackenfrondbiomassaddedtothesoilannually(Znerold1979).OntheClearwaterNationalForest,rhizome and fine root biomass in the fern-invaded communities averaged4000g/m2(Jimenez2005);inthenaturalglade,rhizomeandfinerootbiomassaveraged3200g/m2.ItisnotsurprisingthatthisvegetationtypehashigherCcon-centrations.WeexpectedthatthenaturalbrackenferngladewouldhaveasmuchCasthefern-invadedclearcut,butthiswasnotthecase.Thenaturalbrackenferngladesoilappearstobeatanintermediatepointbetweentheundisturbedforestandthefern-invadedclearcut.TheseresultsaresimilartoCandNdatacollectedfromnearbysiteswithintheGFM(Johnson-Maynardandothers1997).Oneex-planationmaybethatthenaturalbrackenferngladehasreachedasteadystate.

Table 3—Mean C, N, Ca, Mg, and K in the control treatment, by vegetation type and depth. Each mean is an average of three replications.

National Vegetation Forest type Carbon Nitrogen Calcium Magnesium Potassium

- - - - - - percent - - - - - - - - - mg/kg - - - 0-5 cm depthClearwater Undisturbed forest �.�0 a‡ 0.40 a 12.21 d 1.12 b 1.�4 bNez Perce Undisturbed forest 7.�7 b 0.74 c 14.1� e 1.14 b 0.99 aClearwater Partial cut �.2� a 0.�� a 7.�� b 0.74 a 0.99 aClearwater Natural bracken fern glade 7.9� b 0.�1 b �.�� a �.29 d 2.77 cClearwater Bracken fern-invaded clearcut 11.27 c 0.�9 bc �.70 a 2.�4 c 2.�9 cNez Perce Coneflower-invaded clearcut �.17 a 0.�� a 9.1� c 0.92 a 1.02 a 10-15 cm depthClearwater Undisturbed forest �.17 a 0.24 a �.41 c 0.74 d 1.22 cNez Perce Undisturbed forest �.90 b 0.22 a �.�� c 0.41 a 0.71 bClearwater Partial cut �.�� ab 0.2� a �.79 b 0.49 c 0.71 bClearwater Natural bracken fern glade �.90 c 0.4� c 4.2� b 1.�� e 2.20 eClearwater Bracken fern-invaded clearcut 10.00 d 0.�7 d 2.72 a 0.77 d 1.�0 dNez Perce Coneflower-invaded clearcut �.27 c 0.�4 b �.�� c 0.4� b 0.4� a‡ Within soil depth, means followed by different letters are significantly different (p = 0.05) using LSMEANS.



Becausebrackenfernproduceshighlevelsofallelopathicchemicals(FergusonandBoyd1988),itisperhapsbecomingautotoxic(GliessmanandMuller1978),whichresultsinlessfrondbiomass(naturalglade678g/m2;fern-invadedclearcut916g/m2(Jimenez2005))andlessorganicCincorporatedintothesoil.Thesetwotypesofbrackenfernstands(naturalgladeandinvadedclearcut)mayalsobeatdifferentlifecyclestages(Atkinson1986).

HighersoilCconcentrationsinthefern-invadedclearcutareconsistentwiththedevelopmentofnonallophanicsoilcharacteristicsfollowinginvasion(Nanzyoandothers1993;Johnson-Maynardandothers1997;Dahlgrenandothers2004).IncreasedlevelsofCinthebrackenfernsites,ascomparedtoundisturbedsoils,may increase the potential for preferential formation of Al-humus complexes(Dahlgrenandothers1993).

ForestsitesinvadedbywesternconeflowermaintainedmoderatelevelsofCthroughoutthesamplingdepths.Atthe10-15cmdepththeconeflower-invadedclearcuthadnearlytwiceasmuchCastheundisturbedforestsoil(table3).Car-bonwasdistributeddeeperinthesoilprofileintheconeflower-invadedclearcutthanonthebrackenfernsites.Thismaybebecausetheconeflower-invadedsitehadgreatersurfaceandsubsoilmixingcausedbypocketgophers(FergusonandAdams1994)orbecauseofslightlylesssurfacevolcanicashdeposition(Sommer1991).

Foreachvegetationtype,therewasgenerallymoreNinthe0-5cmdepththaninthe10-15cmdepth,withtwonotableexceptions.Boththefern-invadedclearcutandtheconeflower-invadedclearcutsoilshadasmuchNinthe10-15cmdepthasthesurfacesoil.Thisislikelycausedbythelargeannualinputsofforbbiomassthatusuallyoccurinnewlyinvadedclearcuts(Attiwillandothers1985).

RegressionanalysesshowedthattotalCandNwereunchangedafteralteringpH.Thisresultwasnotunexpectedsincewedidnotaddorganicmatter.

Base Cation Concentrations

Basedonthecontrolsamples,vegetationtypedoesinfluencesoilCa,Mg,andKconcentrationsinthesevolcanicashsoils(table3).Forbothsoildepths,theferngladeandthefern-invadedclearcuthadsignificantlymoreKandMgthansoilsfromundertheothervegetationtypes.Incontrast,Cacontentwasgreatestinsoilsunderbothundisturbedforests.

Regressionanalysisshowedthatbasecationconcentrations(Ca,Mg,andK)didnotchangeasaresultofpHchanges(datanotshown).OurresultsdifferfromthoseofMohebbiandMahler(1988)whofoundastrongcorrelationbetweenpHandcationconcentrationafterartificiallychangingpHinaloessalsoil.Intheirstudy,aspHincreased,bothKandMgdecreased;however,CasharplyincreasedfrompH5to7.ItalsoincreasedafterpHdroppedbelow3.5.Itisunusualthatsoilconsistingofvolcanic-ashinfluencedmaterials,whichhaveavariablecharge,didnotshowamarkedreductionintheretentionofexchangeablebaseswithdecreasingpH.Thisindicatestheremaybeenoughpermanentchargemineralstomaintainbaseconcentrations.Intheferngladeandthefern-invadedclearcut,soilsmaybedevelopingpropertiestypicalofnonallophanicAndisols(Johnson-Maynardandothers1997).

LackofpH-drivenchangesincationconcentrationinourstudymayberelatedto high organic C content of the ash-influenced soil (Shoji and others 1993).Theoretically,oncethesesitesareharvested,substantiallossesofbasiccationsare

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possible.Bothlossofnutrientsfromabovegroundpools(Boyleandothers1973;Federerandothers1989)andincreasedleachinglosseshavebeenreportedafterharvesting(Hendricksonandothers1989).However,cationsmayberedistrib-utedintonew,immediateregrowthofbrackenfernorwesternconeflowerafterharvestingandnotlostfromthesite(Johnsonandothers1997).

Available Phosphorus

Phosphorus(P)amountsvariedsignificantlyamongvegetationtypesandsoildepths.ThemeanvaluesforPinthecontroltreatmentareshownintable4.ThelargestPmeansareinthe0-5cmdepthundertheundisturbedforests(NezPerceNationalForest3.17μg/gandClearwaterNationalForest3.03μg/g).Thefernglade(2.73μg/g)andfern-invadedclearcut(2.20μg/g)wereintermediateinP,andthelowestmeanswereintheconeflower-invadedclearcut(1.87μg/g)andpartialcut(1.70μg/g).

RegressionanalysesshowedthatPincreasedwithdecreasingpH.ResponseofsoilPwassimilaratbothsoildepths;therefore,regressionequationsareshownonlyforthe0-5cmdepth(table5).Thevegetationtypeshadsimilarresponse

Table 4—Mean P, potentially mineralizable N (PMN), nitrate (NO�-N), aluminum (Al), and total acidity in the control treat-ment, by vegetation type and soil depth. Each mean is the average of three replications.

National Vegetation Forest type P PMN NO3-N Al Total acidity

µg/g - - - - - - mg/kg - - - - - - - - - - - -cmol/kg - - - - - 0-5 cm depthClearwater Undisturbed forest �.0� c‡ 100.41 b �7.7� a 0.17 a 0.2� aNez Perce Undisturbed forest �.17 c �0.1� ab 172.01 b 0.22 a 0.41 abClearwater Partial cut 1.70 a 14.9� a 10�.1� a 0.�4 ab 0.�� bcClearwater Natural bracken fern glade 2.7� c 7.�� a 2�0.07 bc 0.�4 b 0.7� cClearwater Bracken fern-invaded clearcut 2.20 b ��.�2 ab 24�.99 c 1.14 c 1.77 dNez Perce Coneflower-invaded clearcut 1.�7 ab 2.14 a 97.�1 a 0.2� a 0.�4 ab 10-15 cm depthClearwater Undisturbed forest 1.�0 c �.�� a 24.0� a 0.1� a 0.�1 aNez Perce Undisturbed forest 2.10 d ��.�� a ��.�1 a 0.�1 ab 0.9� abClearwater Partial cut 1.40 b 2�.04 a �1.�� ab 0.�0 a 0.�1 aClearwater Natural bracken fern glade 1.�0 b �.97 a 1��.94 c 1.�� b 1.70 bClearwater Bracken fern-invaded clearcut 2.�� e 192.�0 b 127.4� bc �.�� c 4.22 cNez Perce Coneflower-invaded clearcut 0.9� a 29.�1 a 47.�1 ab 0.21 a 0.�1 a‡ Within each soil depth, means followed by different letters are significantly different (p = 0.05) using LSMEANS.

Table 5—Regression equations for 0-� cm depth (bold lines on figs. �, �, and �).

Y= exp (βo +β1*pH) and Y, βo, and β1 take on the following values:

Definition Dependent(Y) βo β1

P concentration PHOS 2.�7�9 –0.��12Potentially mineralizable N PMN 10.449� –1.44�7NO�-N concentration NO�-N –7.14�2 2.2212KCl-extractable Al ALUM 10.�40� –2.2�14Total acidity ACID 9.9�7� –2.0�2�



surfaces(fig.3).SoilfromtheClearwaterNationalForestundisturbedforesthadthehighestavailablePwhenpHdroppedbelow4.0.Bothhumusandallophanecontentinvolcanicash-influencedsoilsaffectPavailabilityandthehighlevelofCinthefern-invadedclearcutsoilmaybesorbingP(Wada1985).Theseresultsarequitedifferentfromtheloessalsoilsthathaveastronglinearincreaseinavail-ablePaspHincreases(MohebbiandMahler1988).Forvolcanicash-influencedsoils,thepHdependencyofphosphatesorptionishighestbetweenpH3and4,andgenerallydecreaseswithincreasingpH(Nanzyo1987).Thisisespeciallytrueforallophanicash-influencedsoilsascomparedtononallophanicash-influencedsoils(Nanzyoandothers1993).

Insoilsconsistingofweatheredvolcanicash,Psorptionisamajorsoilfertilityproblem(AndreggandNaylor1988).Inmostmineralsoils,organicmatterisanimportantreservoirforP.However,inmanyvolcanicash-influencedsoils,organicmatterprotectsPfromsorption(Moshiandothers1974).Thisappearstobethecaseforthesesoilsaswell.

Figure 3—Regression equations for available P concentration (µg/g) of the 0-� cm depth as affected by pH manipulation by vegetation type. The bold line is the regression for all vegetation types.

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Potentially Mineralizable N and Nitrate-N

PotentiallymineralizableN(PMN)concentrationsvariedwidelyamongveg-etationtypesandsoildepths(table4).Forexample,inthecontrolsoilforthe0-5cmdepth,PMNrangedfromalowof2.14mg/kgintheconeflower-invadedclearcutto100.41mg/kgintheundisturbedforestontheClearwaterNationalForest.AmountsofPMNatthe0-5cmsoildepthwaslowinthefernglade,butintermediateinthefern-invadedclearcut.

Nitrate-N(NO3-N)alsovariedamongvegetationandsoildepths.Thelargestmeansatthe0-5cmdepthforthecontrolsoil(table4)wereinthefern-invadedclearcut(246.99mg/kg)andfernglade(230.07mg/kg),andthelowestmeanwas87.73mg/kgintheundisturbedforestsoilfromtheClearwaterNationalForest.MeansforNO3-Natthe10-15cmdepthwerelowerthanthe0-5cmdepth,butthetrendsweresimilar.

AnalysesshowedthatPMNconcentrationsdeclinedrapidlyassoilpHincreasedabove5.0and,incontrast,soilNO3-NconcentrationincreasedrapidlyabovepH5.0,exceptintheferngladeandfern-invadedclearcutwherethischangeinNformoccurredbelowpH4.5(fig.4a-f).WhilethesoilsinbothundisturbedforestsandthepartialcutforestsexhibitedathresholdlevelofpH5.0forsub-stantialchangesinthequantityofavailableN,thetwositeswithbrackenfernvegetationtypesandtheconeflower-invadedclearcuthadsteadychangesinNaspHincreased.Bothsoildepthshavesimilarregressioncurvesforeachvegetationtype;therefore,onlythe0-5cmsoildepthisshown(table5).

The sharpdecline inPMN from theseash-influenced sites isdifferent fromthenorthernIdaholoessalsoils,whichhadasignificantincreaseinPMNaspHincreasedfrom3.0to7.0(MohebbiandMahler1988).Thismayindicateadiffer-enceinorganicmatterconcentrationfromloess-grasslandareastoash-forestedareas,andsuggeststhatorganicNinvolcanicash-influencedsoilsmaybefairlyresistanttomicrobialdecompositionbecauseoftheAl-organiccomplexesthatareformed(Shojiandothers1993).

Whilesoilfrommostofthevegetationtypesshowacrossoverinrelativeabun-danceofPMNandNO3-NaroundpH5.0,thebracken-ferndominatedvegetationtypeschangebelowpH4.5.IncreasedNO3

-NanddecreasedPMNathigherpHvaluesisconsistentwithresultsofacidrainandsoilnutritionstudies(Schier1986;Marx1990).NitrogenmineralizationoftenincreaseswhensoilpHisraised(MontesandChristensen1979),butoccasionallyhasbeenshowntodecrease(AdamsandCornforth1973).NitrificationisalsopHsensitiveandgenerallyincreasesaspHisraisedfromveryacidtomoderatelyacid(Robertson1982).Inthisstudy,theclearcutsinvadedwitheitherbrackenfernorwesternconeflowerlikelyexhibitthisNchangeeachyearaspHchanges(BinkleyandRichter1987).

Aluminum and Total Acidity

KCl-extractableAl (whichreflectsexchangeableAl)and totalacidityvariedsignificantlyamongvegetationtypesandsoildepths.Meanvaluesinthecontroltreatments are shown in table4.Aluminumand total acidity are significantlyhigherintheferngladeandfern-invadedclearcut,forbothdepths.MeanAlandacidvaluesaregenerallyhigherinthe10-15cmdepthsoilascomparedtothe0-5cmdepth.

19� USDA Forest Service Proceedings RMRS-P-44. 2007


Figure 4—Soil NO�-N and PMN concentration (mg/kg) in the 0-� cm depth as affected by pH manipulation, by vegetation type (a) Clearwater National Forest, undisturbed, (b) Nez Perce National Forest, undisturbed, (c) Clearwater National Forest, partial cut, (d) Clearwater National Forest, bracken fern glade, (e) Clearwater National Forest, bracken fern-invaded clearcut, (f) Nez Perce National Forest, coneflower-invaded clearcut.

(a) (b)

(c) (d)

(e) (f)



RegressionanalysesshowedthatAlwashighlycorrelatedwithchangesinpH(table5)inallvegetationtypes.AluminumincreasedexponentiallywhenthepHdecreasedbelow4.5(fig.5).Both0-5cmand10-15cmdepthshadsimilarcurves;therefore,onlythe0-5cmsoildepthregressionlinesareshown.Volcanicash-influencedsoilscontainhighlevelsofAl-containingmaterialsthatcanundergodissolutionunderacidic(lessthatpH5.0)conditions(Tisdaleandothers1993).Inthesesoils,verylittleexchangeableAlwasdetectedabovepH5.0.BasedoncontinuoussoilmeasurementsofpH(figs.1and2),soilsunderbrackenfernandconeflowervegetationhaveapHbelow5.0eachgrowingseason.SoilpH5.0isgenerallyconsideredtobethecriticalpointforAltoxicitytowoodyvegetation(Wolt1994).

Ingeneral,woodyplantspeciesappeartobemoretolerantofAlthanagricul-turecrops(McCormickandSteiner1978;Ryanandothers1986),andthereisconsiderablevariationinAltoleranceamongtreespecies(McCormickandSteiner1978;Steinerandothers1984;ArpandOuimet1986;Hutchinsonandothers1986;Schaedleandothers1989;Raynalandothers1990).Aluminumtoxicityalterstreerootanatomy,whichfirstoccursintheroots(Hutchinsonandothers1986;Schaedleandothers1989;McQuattieandSchier1990;NoskoandKer-shaw1992;Schier1996).TheresultofAltoxicityisimpairedrootdevelopment,resultinginreducedrootlengthandformationofashallowrootsystem.Athigh

Figure 5—Exchangeable Al concentration (cmol/ kg) in the 0-� cm depth as affected by pH, by vegetation type. The bold line is the regression for all vegetation types.

19� USDA Forest Service Proceedings RMRS-P-44. 2007


Allevels,mitosisisalmostcompletelyinhibited.Leamy(1988)notedthatinvol-canicash-influencedsoils,Altoxicitymayoccuratconcentrationsof2cmol/kgsoil,andthisvalueisusedasathresholdinSoilTaxonomyforidentifyingthoseAndisolsinwhichAlphytotoxicitymayoccur(SoilSurveyStaff2003).Aluminumlevelsfoundinthislaboratorystudyaremuchhigherthan2cmol/kgwhenpHdecreasedbelow5.0andindicatesastrongpotentialforAltoxicityintheseash-influencedsoilsaspHvaluesdecline.

ThevariousstudiesonAltoxicityintreespeciesaredifficulttocomparebecauseofdifferent studymethods,unitsofmeasure,growthmedia, lengthofexperi-ments,andageoftrees(Schaedleandothers1989;NoskoandKershaw1992).However,oneimportantfindingisthatyoungseedlingsaremoresensitivetoAltoxicitythanolderseedlings.Forexample,Schier(1996)foundthatAlconcentra-tionsof0.32mM/linhibitedrootbiomassinnewlygerminatedredspruce(Picea rubens)seedlings,whilethethresholdwas2.1mM/lin1-year-oldseedlings.ItseemsreasonabletoassumethatconiferseedgerminatingonGFMsitescouldbeimpactedbylowconcentrationsofAl.Aluminumtoxicity,allelopathiccom-pounds,andcompetitioncouldcombinetoeliminatethenaturalestablishmentoftreesandotherwoodyplantspeciesonthesesites.

Regressionanalyses for totalacidity followed thesame trendasextractableAl(fig.6),andonlythe0-5cmsoilregressionlinesareshown.Theregressionequationfortotalacidityisshownintable5.Mostoftheacidityinthesesoils

Figure 6—Total acidity (cmol/kg) in the 0-� cm depth as affected by pH manipulation by, vegetation type. The bold line is the regression for all vegetation types.



occursasAl.TherelationshipbetweenexchangeableAlandtotalacidityisnotunusual sincemost of the exchangeable acidity is derived fromAl andHontheexchangesites(BinkleyandRichter1987).Changesinexchangeableaciditygenerallyoccuroveralongperiodoftimeandareduetoacidificationthroughweathering,leaching,cationuptake,oratmosphericdeposition(Richter1986).RapidchangesinacidityoccuroccasionallybyotherH-ioninputs.IntheGFM,bothbrackenfernandwesternconeflowervegetationhavethepotentialtoinputH-ionsviaorganicacidproductionoradditionsofhighamountsoforganicCthroughyearlyvegetationcycles.

Summary ______________________________________________________Analysis of unaltered soil samples supporting undisturbed grand fir forest

andbrackenfern/westernconeflowerplantcommunitiessuggeststhatchemicalpropertiesofGFMforestsoilarealteredthroughinvasionofsuccessionalplantspeciesaftertimberharvestorotherdisturbance.Changesinsoilconditionsaresimilartoadepthof15cm.SeasonaldecreasesinsoilpHunderbrackenfernandwesternconeflowervegetationtypesmostlikelycauseareleaseofexchangeableAlatlevelstoxictowoodyvegetation.HighlevelsofC,exchangeableAl,andtotalacidityunderthesetwovegetationtypesmayalsobefacilitatingalocalizedconversionoftheseash-influencedsoilsfromallophanictononallophanicAndis-ols.ForestedsoilsintheGFMarecapableofexhibitingthesesamecharacteristicsoncedisturbed.

Resultsofthisstudyalsoprovideinsightsintothechemicalchangesthatmayoccurinvolcanicash-influencedsoilsaspHfluctuates.Mechanismsthatcon-tributetoforb-dominatedsecondarysuccessionalplantcommunitieshavebeenidentified.Forexample, theapparentchangeinNbetweenPMNandNO3-Nhasimplicationsindeterminingwhichspeciescangrowonthesesites,asdoestheexponentialincreaseofAlbelowpH5.0.Clearly,thislaboratorystudypointsoutthepotentialforAltoxicitythatmayaccompanyseasonalpHfluctuations.Theselaboratorystudyfindingsareconsistentwithin situsoilsolutiondata,whichindicate that soils invaded by bracken fern and western coneflower undergoconversionfromallophonictononallophanicproperties(Johnson-Maynardandothers1997).However,alteringthepHofash-influencedsoilsdifferedfromal-teringloessalsoils(MohebbiandMahler1988).Thesesoil-typedifferencesarelikelyattributabletotheuniquephysical,chemical,andbiologicalpropertiesofash-influencedsoilsascomparedtothosederivedfromotherparentmaterials(Dahlgrenandothers2004).

This laboratory study highlights important characteristics of ash-influencedsoilsthatmaycontributetochangesinvegetation.Thistypeofstudy,combinedwithfieldwork,willhelpinthedevelopmentofpracticalmanagementrecom-mendations.

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