Ash Cap Influences on Site Productivity and Fertilizer ... · Garrison-Johnston, Mika, Miller, Cannon, and Johnson Ash Cap Influences on Site Productivity and Fertilizer Response

1�7USDA 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.

Mariann T. Garrison-Johnston and Peter G. Mika are research scientists and Leonard R. Johnson is the director for the Intermountain Forest Tree Nutrition Cooperative, University of Idaho, Moscow, ID. Dan L. Miller is a silviculture manager for Potlatch Corporation, Lewiston, ID. Phil Cannon is the productivity manager for Forest Capital, North, Monmouth, OR.

Abstract Datafrom139researchsitesthroughouttheInlandNorthwestwereanalyzedforeffectsofashcaponsiteproductivity,nutrientavailabilityandfertilizationresponse.Standproductivityandnitrogen(N)fertilizerresponseweregreateronsiteswithashcapthanonsiteswithout.Whereashwaspresent,depthofashhadnoeffectonsiteproductivityorNfertilizerresponse.Siteproductivityincreasedwithincreasingpotentiallyavailablesoilwater.Potentiallyavailablesoilwater,inturn,increasedwithincreasingashdepth.Decreasingavailabilityofmagnesium(Mg)andcalcium(Ca)intheupper12inchesofsoilmayhaveconstrainedsiteproductivitywithincreasingashdepth.SoilmineralizableNandammoniumNwereunaffectedbyashpresenceordepthbutdidvarybyunderlyingparentmaterial.SiteproductivityandNfertilizerresponsevariedbyunderlyingparentmaterialevenafteraccountingforashpresence.Standvolumeresponsetosulfur(S)fertilizationdecreasedwithincreasingashdepth,suggestingpossibleSadsorptionbyashcap.NogrowthresponseorchangeinfoliarKstatuswasdiscernedfollowingKfertilization.Managementrecommendationsbyparentmaterialareprovided.

Ash Cap Influences on Site Productivity and Fertilizer Response in Forests of the Inland

NorthwestMariann T. Garrison-Johnston, Peter G. Mika, Dan L. Miller, Phil Cannon, and

Leonard R. Johnson

Background

Availabilitytoplantsofmostnutrientsbesidesnitrogen(N)isrelatedprimarilytomineralweatheringratesandsoilphysicalandchemicalproperties.CommonparentmaterialsofsoilsintheInlandNorthwestincludetheColumbiaRiverbasaltflows,BeltSeriesmetasedimentaryrocks,granites,andvariousglacialdeposits.Characteristicsthatthesematerialsimparttofor-estsoilssignificantlyaffectforestnutrition,productivityandresponsetofertilization(MooreandMika1997;Mooreandothers2004).However,surficiallydepositedparentmaterialsareoftenneglectedduringanalysesofparentrockeffectsonforestnutrition.ThisisparticularlytrueforwidespreadvolcanicashresultingfromtheeruptionofMountMazama(nowCraterLake)insouthwesternOregon.Theeffectsofsurficiallydepositedparentmaterialsonforestnutrition,productivityandresponsetofertilizationarepoorlyunderstood.

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

Garrison-Johnston, Mika, Miller, Cannon, and Johnson Ash Cap Influences on Site Productivity and Fertilizer Response in Forests of the Inland Northwest

Ash-capsoilscommontotheInlandNorthwestareknownfortheircapabilitytoholdampleavailablemoisture,whichinturnisthoughttoenhancesitepro-ductivity (BrownandLowenstein1978;Mital1995).Becauseof theimprovedsoilmoisturestatus,foreststandsgrowingonash-capsoilsaregenerallyexpectedto show greater growth response to nitrogen (N) fertilization than stands onsoilswithoutashcap,atleastsolongassomeotherfactorisnotmorelimitingthan moisture and/or N. In a study of 90 Douglas-fir fertilization trial standsacrosstheInlandNorthwest,Mital(1995)foundapositivecorrelationbetweenDouglas-firgrowthresponsetoNfertilizationandashdepthatanapplicationrateof400lbac–1,whiletherelationshipwaslessstrongwhentheapplicationratewas200lbac–1.Inanotherstudy,Geist(1976)reportedthatforageproductiononvolcanicashsoilsshowedstrongfertilizationresponseonforestedrangesitesineasternOregonandWashington.

Withoutfertilizersorblendingwithorganicmatter,unweatheredash-capsoilsarenotparticularlyfertile,beingcomprisedlargelyofpoorlycrystallinealumi-nosilicatesandiron(Fe)andaluminum(Al)oxides.Theirnutrientcationstoragecapacity is low, suggesting that supply of the nutrient cations potassium (K),calcium(Ca)andmagnesium(Mg)maybepoor(McDanielandothers2005).Furthermore,stronganionadsorptioncapacitybyvolcanicashmayimpedetreefertilizationresponse.Inastudyofsulfur(S)adsorptionpropertiesofandicsoilsintheInlandNorthwest,Kimseyandothers(2005)suggestthatappliedSfertilizersmaybeineffectiveinincreasingS-availabilitytotreesunlessathresholdsorptioncapacityof theashcapisexceeded.Similar interactionsmaybeexpectedfortheanionicformsofotherelements,includingN,phosphorus(P)andboron(B).Suchaphenomenonmayexplain,inpart,thevariablerelationshipbetweenashcapdepthandN-fertilizationratesdescribedbyMital(1995),ifsomethresholdsorptioncapacityhadtobemet(suchasatthe400lbrate)beforetheappliedNbecameavailabletotheforestvegetation.Theashcapmaytakeonnutritionalcharacteristicsofunderlyingresidualsoils,thoughthisperceptionhasnotbeenscientificallytested.

AstatisticalanalysisofdatafromnutritionalresearchconductedbytheInter-mountainForestTreeNutritionCooperative(IFTNC)from1980tothepresentwasundertakentodeterminewhetherashdepositsaffectedtreeandsoilnutrition,for-estproductivityandfertilizationresponse.Wehypothesizedthatsiteproductivityandfertilizerresponsewouldbegreateronashsitesthannon-ashsitesandthatproductivityandresponsewouldincreasewithincreasingashdepth.

Methodology ___________________________________________________

Data Compilation

Data from139 IFTNC research siteswere compiled.Thedata set included94sitesfromthe1980-1982Douglas-firStudy,8siteseachfromthe1991and1993MixedConiferStudies,and29sitesfromthe1994-1996ForestHealthandNutritionStudy(table1).Soilprofiledescriptionswereusedtoestimateorganichorizondepth,surficialdepositdepthandresidualsoildepthto36inches.Sur-ficial deposits were categorized as ash, loess, glacial deposits, other modern(quarternaryera)deposits,andtertiarydeposits.Residualsoilswerethosederivedfromthebasegeology.Thedivisionbetweensurficialdepositsandbasegeology


Ash Cap Influences on Site Productivity and Fertilizer Response in Forests of the Inland Northwest Garrison-Johnston, Mika, Miller, Cannon, and Johnson

Tabl

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List

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140 USDA Forest Service Proceedings RMRS-P-44. 2007


wasnotalwaysclear.Becausethesoildepthparameterforthisstudywaslimitedto36inches,deepsurficialdepositswereoftentheonlyparentmaterialnoted.Therefore,thebasegeologicparentmaterialcategoriesforthispaperincludedbasalt,granite,sedimentaryrock,metasedimentaryrock,glacialdeposit,tertiarysedimentsandmodernsediments.Ashwasconsideredpresentifitwascontinu-ousandmeasurabletoadepthof1inchorgreater.Admixturesofashandothermaterialswerealsocountedasashcapiftheashwasapredominantandidentifi-ablecomponentofthemix.

Soilwater-holdingcapacitywasdetermined for theupper24 inchesof thesoil profile on 110 sites. Potential plant-available water was calculated as thedifferenceinmoisture-holdingcapacitybetween1/3and15barsforthosesites.Conventionallaboratorysoiltestswereperformedontheupper12inchesofsoilforall139sites,thoughsometestswereperformedononlyasubsetofthesites.AvailablePandKweretestedusingsodiumacetateextraction,whileNH4+andNO3–wereanalyzedusing2MKClextractionwithanalysisbycolorimetry(CaseandThyssen1996a;CaseandThyssen1996d).Sulfate-sulfurwasanalyzedbycalciumphosphateextractionandionchromatography,andBwasanalyzedbycalciumchlorideextractionandspectrophotometricdetermination(Case1996;CaseandThyssen1996c).ExtractableCa,Mg,KandNawereanalyzedby1NammoniumacetateextractionandICP,andmicronutrientsCu,Zn,MnandFebyDTPA(CaseandThyssen1996b;CaseandThyssen2000).

Twodifferentapproacheswereusedtoestimatesiteproductivity.Thefirstap-proachutilizedDouglas-firsiteindex(SI,Monserud1984),availablefor110ofthe139sites.Wealsoselectedcontrolplotgrowthrate(CGR)asaneasilycal-culatedproductivityestimateavailableforallsitesincludedinthestudy.Controlplotgrowthratewasestimatedastheaveragegrowthrateinft3ac–1yr–1overthefirst6yearsofeachstudy.Fertilizationresponsewasbasedon6-yearcubicfootvolumeresponse(ft3ac–1yr–1)toNfertilizersappliedat200to300lbNac–1.LimiteddatawereavailableforexaminationofvolumeresponsetoSfertilizersappliedat100lbSac–1andKfertilizersappliedat170lbKac–1.

Treenutritionwasassessedbychemicalanalysisoffoliagecollectedoneyearafterfertilizationfromtheupperthirdofthecrownondominantorco-dominanttrees.Becausefoliagechemistrydiffersfordifferenttreespecies,Douglas-firwasselectedforinclusioninthisanalysisasthespeciesmostcommonlyoccurringacrosstheselectedtestsites.Nutrientdeficiencieswereidentifiedbythecriticallevelsmethod,definedasthepointonayieldcurvewhereanincreaseinnutri-entconcentrationnolongerresultsinincreasedyield.Thus,the“criticallevel”istheoptimumnutrientconcentrationatwhichmaximumyieldisobtainedwithminimumnutrientinput.CurrentlyacceptedcriticallevelsforInlandNorthwestDouglas-firfoliageareshownintable2.

Data Analysis

Sites were arrayed in a matrix by geographic region, rock type, vegetationseriesandashcappresenceorabsencetoevaluatesamplesizesineachcategory.Analysisofvariancewasusedtodetecttheeffectsofregion,rocktype,vegetationseriesandashpresenceonsiteproductivity,soilandfoliagecharacteristicsandfertilizationresponse.Thebasicstatisticalmodelusedforthisanalysiswas:

Yijk=µ+αj+βk+(αβ)jk+εijk (1)

141USDA Forest Service Proceedings RMRS-P-44. 2007


Table 2—Nutritional critical levels for Douglas-fir foliage. Adapted from Webster and Dobkowski (19��).

Nutrient Unit of concentration Critical levelNitrogen (N) % 1.40Phosphorus (P) % 0.12Potassium (K) % 0.�0Sulfur (S) % 0.11Calcium (Ca) % 0.1�Magnesium (Mg) % 0.0�Manganese (Mn) ppm 1�Iron (Fe) ppm 2�Zinc (Zn) ppm 10Copper (Cu) ppm 2Boron (B) ppm 10

Where:

Yijk=theproductivity,soilorfoliagecharacteristicmeasuredateachsiteµ=populationgrandmeanforproductivity,soilorfoliagecharacteristicαj=effectofregion,parentmaterialorvegetationseriesβk=effectofashpresenceorabsence(dummyvariable)(αβ)jk=effectofregion,parentmaterialorvegetationseriesbyashcapinteractionεijk=theerrorterm~NID(0, σ2)

BecauseCGRwasafunctionofinitialvolume,analysesofCGRincludedinitialvolumeasacovariateintheabovemodel.Similarly,becausefertilizationresponsedependedonstartingvolumeandstandgrowthrate,thosevariableswereusedascovariatesforthatanalysis.Ashdepthasacontinuousvariablewasalsoincor-poratedintotheabovemodeltoperformregressionanalysisoftheeffectsofashdepthonallvariablesexaminedinthisstudy.Resultswereconsideredsignificantatthe90%confidencelevel(p=0.10).

Results _________________________________________________________

Ash Distribution

SitesinnorthIdaho,northeastWashingtonandnortheastOregonweremorelikelytohaveashthansitesincentralWashington,MontanaandcentralIdaho(table3).Sitesontertiarydeposits,metasedimentaryrocksandglacialdepositsweremorelikelytohaveashthanthoseonbasalt,granite,modernsedimentarydepositsandsedimentaryrocks.Almostallwesternredcedarandwesternhemlockvegetationseriesoccurredonsiteswithash,whileonlyabouthalfthegrandfirseriesandaquarteroftheDouglas-firseriesoccurredonsiteswithashcap.Thestatisticaltermforthispatternwherebyashoccursinconjunctionwithcertaincharacteristicsandnotothersisknownas“confounding.”Confoundingbetweenashpresenceandothersitecharacteristicsmakestatisticalanalysisdifficultbecausewecannotdeter-minewhetherproductivityorresponsedifferencesbetweensitesareduetotheashpresence/absenceortheothersitecharacteristic(vegetationseries,parentrockorgeographicregion).Theoccurrenceofashinconjunctionwithcertainparentrocks



orgeographicregionsislikelycoincidental,whiletheoccurrenceofashinconjunc-tionwithcertainvegetationseriesismoresuggestiveofacausalrelationship.

Site Productivity

Douglas-firSIwasanalyzedfor110sites(SIinformationwasnotavailablefortheForestHealthandNutritionStudysites).Overall,SIwas10.6%greateronsiteswithashcapthansiteswithout.BaseparentmaterialexplainedasignificantamountofSIvariation(R2=0.18),andtheadditionofashpresencetothismodelexplainedsomeadditionalvariationinSI(R2=0.28;fig.1a).Onallparentmaterialtypesexceptbasalt,thepresenceofashcapsomewhatincreasedsiteproductivitycomparedtothenon-ashsites.However,givenashpresence,asubsequentregres-sionanalysisrevealednosignificantinfluenceofashdepthonSI(fig.1b).AverageSIdidvarybygeographicregion(fig.1c);however,ashpresenceorabsencedidnotfurtherexplainvariationinSIoncethegeographicregionwasknown.Similarly,whileasignificantamountofvariationinSIwasexplainedbyvegetationseriesalone(fig.1d),ashpresencedidnotexplainanyfurthervariation.

Controlplotgrowthratewasavailableforall139sitesincludedintheanalysis,andwashighlycorrelatedwithSI(R2=0.59).Overall,CGRwas29.0%greateronashversusnon-ashsites.AshdepthdidnotaffectCGR(fig.2a).Controlplotgrowthratewassignificantlyaffectedbygeographicregion(R2=0.58;fig.2b),

Table 3—Number of research sites with and without ash cap by region, underlying geology and vegetation series.

Ash cap present? Percent sites Region no yes Total with ash cap

North Idaho � 2� �1 �4%Northeast Washington � 17 2� 74%Northeast Oregon 7 10 17 �9%Central Washington 2� 11 �4 �2%Montana 14 2 1� 1�%Central Idaho 17 1 1� �% Underlying geology

Tertiary deposits 1 � 7 ��%Metasedimentary rocks � 20 2� 71%Glacial deposits � 17 2� ��%Basalt 2� 1� �� 4%Granite 1� 9 27 ��%Modern deposits 7 2 9 22%Sedimentary rocks � 0 � 0%

Vegetation series

Western red cedar 1 22 2� 9�%Western hemlock 1 � � ��%Grand fir 29 24 �� 4�%Subalpine fir � 2 � 40%Douglas-fir �� 14 �2 27% Total sites with and without ash cap: 72 67 139 48%

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


Figure 1a—Douglas-fir site index by base parent material and ash cap presence. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).

Figure 1b—Douglas-fir site index (ft at �0 years) by ash cap depth for sites with ash cap.

Figure 1d—Douglas-fir site index by vegetation series. Vegetation series include Douglas-fir (DF), grand fir (GF), subalpine fir (SAF), western hemlock (WH) and western red cedar (WRC).

Figure 1c—Douglas-fir site index by geographic region. Regions include central Idaho (C ID), central Washington (C WA), Montana (MT), north Idaho (N ID), northeast Oregon (NE OR) and northeast Washington (NE WA).



vegetation series (R2=0.59; fig. 2c) and dominant parent material (R2=0.46;fig.2d).Ashpresencedidnotexplainanyadditionalvariationforthegeographicregionorthevegetationseriesmodels.However,ashpresencedidexplainsomeadditionalvariationinCGRintheparentmaterialmodel(R2=0.57;fig.2e).TheresultsweresimilartothoseforSI,withashpresencesomewhatincreasingCGRformostparentmaterials.AlsosimilartoSI,onceashwaspresentCGRdidnotchangewithashdepth.

Site Fertility

Soil moisture—Siteproductivityincreasedwithincreasingpotentiallyavailablewater(fig.3a).Potentiallyavailablewater,inturn,increasedwithincreasingashdepth.Whenarrayedbyvegetationseries,potentiallyavailablewaterwasgreater

Figure 2a—Control plot growth rate by ash cap depth for sites with ash cap.

Figure 2b—Control plot growth rate (ft�ac –1yr –1) by geographic region. Regions include central Idaho (C ID), central Washington (C WA),Montana (MT), north Idaho (N ID), northeast Oregon (NE OR) and northeast Washington (NE WA).

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


Figure 2e—Control plot growth rate ft�ac –1yr –1) by base parent material and ash cap presence. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), mod-ern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).

Figure 2c—Control plot growth rate (ft�ac –1yr –1) by vegetation series. Vegetation series include Douglas-fir (DF), grand fir (GF), subalpine fir (SAF), western hemlock (WH) and western red cedar (WRC).

Figure 2d—Control plot growth rate ft�ac –1yr –1) by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedi-mentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).

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


onsitesonwesternredcedarseriescomparedtositesonDouglas-firandgrandfirseries(fig.3b).Whenarrayedbyparentmaterial(fig.3c),siteswithashcapsonbasaltandmetasedimentaryparentmaterialsaveragedhigherpotentialwateravailabilitythanthoseongraniteandglacialtillparentmaterials.However,whenashwasabsent,sitesonglacialtillparentmaterialshadhigherpotentiallyavail-ablewaterthansitesonmetasedimentaryorgraniticrocks.

Soil Acidity—SoilpHdatawereavailablefor135sites.Overall,pHincreasedwithincreasingashdepth.VegetationserieshadasignificanteffectonpH,withsitesonsubalpinefirserieslessacidthanthoseongrandfirorDouglas-firseries,whichinturnwerelessacidthansitesonwesternredcedarorwesternhemlockseries (fig. 4a). Parent material also affected soil pH, but interacted with ash

Figure 3a—Control plot growth rate ft�ac –1yr –1) and Douglas-fir site index (ft at �0 years) as a function of potential available water (inches) in the upper 24 inches of soil.

Figure 3c—Potentially available water (inches) in the upper 24 inches of soil as a function of ash depth (inches), by base parent material. Parent materials include basalt, glacial deposit (glacial), granite and metasedimentary (metased).

Figure 3b—Potential available water (inches) in the upper 24 inches of soil as a function of ash depth (inches), by vegetation series. Vegetation series include Douglas-fir (DF), grand fir (GF) and western red cedar (WRC).



depth(fig.4b).Soilaciditydecreasedwithincreasingashdepthongraniteandperhapsbasaltparentmaterials,andincreasedwithincreasingashdepthonter-tiarysediments,butshowedlittlevariationwithashdepthonotherunderlyingparentmaterials.Intheabsenceofash,soilaciditywasaboutthesameforallunderlyingparentmaterials.

Nitrogen—Soil mineralizable N data were available for 119 sites, whileammonium-Ndatawereavailable for45sitesandnitrate-Ndata for44sites.Noneof these threemeasuresofsoil-availableNvariedwithashpresenceordepth.However,twoofthevariables,soilmineralizableNandammonium-N,variedbyparentmaterial(fig.5aand5b).Bothmeasuresshowedhighervaluesonmetasedimentaryandtertiarydepositparentmaterials,andlowervalueson

Figure 4a—Soil pH by vegetation series. Vegetation series include Douglas-fir (DF), grand fir (GF), subalpine fir (SAF), western hemlock (WH) and western red cedar (WRC).

Figure 4b—Soil pH as a function of ash depth (inches) and base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).

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


graniticandbasalticmaterials.InanefforttodeterminewhyparentmaterialwouldaffectsoilmineralizableN,severaladditionalstatisticalanalyseswereperformedusingdataonpercentorganicmatter(29sites)andpercentcarbon(90sites).Min-eralizableNwasstronglyandpositivelycorrelatedwithbothsoilorganicmatter(R2=0.69)andsoilcarbon(R2=0.68),suggestingthatparentmaterialcouldaffectsoilmineralizableNbyaffectingsoilorganicmatterand/orcarboncontent.

FoliarNconcentrationsofunfertilizedDouglas-firtreeswerebelowthecriticallevelof1.4%formostsites,andweregenerallyunaffectedbyashpresenceordepth.However,foliarNwasaffectedbyunderlyingparentmaterial,withtreesonbasaltparentmaterialsshowinghigherfoliarNconcentrationsthantreesonotherparentmaterialtypes(fig.5c).ExaminationofSIasafunctionoffoliarNshowedapositiverelationship(R2=0.28;fig.5d).Theslopeoftherelationshipdidnotvarybyunderlyingparentmaterial,butSIwashigherontertiarysedimentsandmetasedimentaryrocks.FoliageNconcentrationswerealsoanalyzedasafunctionofsoil-available(mineralizable)N,withtheexpectationthatfoliageNlevelswouldincreasewithincreasingsoilmineralizableNlevels.However,thecorrelationwasveryweak(R2=0.05).Amodelcombiningtheeffectsofrocktype,mineralizableNandelevationbetterdescribedvariationinfoliageN(R2=0.27),withfoliageNpositivelyrelatedtomineralizableNandnegativelyrelatedtoel-evation.Interestingly,thismodelshowedthattreesonbasalt,sedimentaryrockormodernsedimentshadhigherfoliarNconcentrationsthanthoseonglacialtillsormetasedimentaryrocks.Othersitefactorsincludingsoilfertility,soilwaterpotential,aspectandslopewerenotrelatedtofoliageN,andfoliageNdidnotvarybyvegetationtypeorgeographicregion.ThissuggestedthatunderlyingrockdidsomehowinfluencefoliageNnutrition.

Cations—Extractablecationdatafromsoilsamplesfrom119sitesindicatedthatextractableKwasnotaffectedbyashcappresenceordepth,butwasaffectedbyunderlyingparentmaterial(fig.6a).ExtractableCaandMgbothdecreasedwithincreasingashdepth(Ca:R2=0.30,fig.6bandMg:R2=0.33,fig.6c).Giventhesamedepthofash,CaandMgwerelowestonsiteswithgraniticparentmateri-alsandhighestonbasaltandmetasedimentaryparentmaterials.Incontrastto

Figure 5a—Soil mineralizable nitrogen (N, ppm) by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedi-mentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).



Figure 5b—Soil ammonium-nitrogen (NH4-N, ppm) by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).

Figure 5d—Site index (ft�ac –1yr –1) as a function of ash depth (inches), by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).

Figure 5c—Douglas-fir foliar nitrogen (N) con-centration (percent) as a function of ash depth (inches), by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).

1�0 USDA Forest Service Proceedings RMRS-P-44. 2007


soilK,Douglas-fir foliarKwasunaffectedbyunderlyingparentrock,butwasconsistentlyhigherinthepresenceofash(fig.6d).Onceashwaspresent,ashdepthhadnoeffectonfoliarK.Douglas-firfoliarCa(fig.6d)andMg(fig.6e)concentrationsbehavedsimilarlytosoilavailabilityinthatbothdecreasedwithincreasingashdepth.UnderlyingparentmaterialdidnotaffectfoliarCaorMgvalues.FoliarK,CaandMgconcentrationsweregenerallyabovenutritionalcriti-callevels(table2).

Phosphorus—Soil-availablePdatawereavailableforonly45sites.Soil-availablePwasnotaffectedbyashpresenceordepth,butwasaffectedbyparentmaterial(fig.7a),withglacialdepositsshowingthehighestPavailabilityandmetasedi-mentaryrocksthelowest.Douglas-firfoliarPvaluesweregenerallyabovecriti-callevels(table2),andwerealsounaffectedbyashpresenceordepth.FoliarPconcentrationsdifferedbyparentmaterial,andwerehighestonglacialdeposits

Figure 6a—Extractable potassium (K, cmol kg–1) by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).

Figure 6b—Extractable calcium (Ca, cmol kg–1) as a function of ash depth (inches), by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).

Figure 6c—Extractable magnesium (Mg, cmol kg–1) as a function of ash depth (inches), by base parent material. Parent materials include basalt, glacial de-posit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).



Figure 6f—Douglas-fir foliar magnesium (Mg) concentration (percent) as a function of ash depth (inches), by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedi-mentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).

Figure 6d—Douglas-fir foliar potassium (K) concentration (percent) as a function of ash depth (inches), by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedi-mentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).

Figure 6e—Douglas-fir foliar calcium (Ca) concentration (percent) as a function of ash depth (inches), by base parent material. Parent materi-als include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).



andlowestonmetasedimentaryrocks(fig.7b).NeitherfoliarPconcentrationsnorsoilPtestssuggestedanyeffectofashonPavailabilityduringthisstudy.

Sulfur, B and Cu—SufficientdatawereavailabletoperformstatisticalanalysesforavailableBandS(45sites)andCu(29sites).Givenashpresence,availableBincreasedwithincreasingashdepth(fig.8a).Therewasnoevidencethatpar-entmaterialorvegetationseriesaffectedsoilBavailability.Incontrast,availableCuwasnotaffectedbyashpresenceordepth,butdidvarybyparentmaterial,ranging from0.46ppmongranitic sites to1.03ppmonmodernsedimentary

Figure 7a—Available phosphorus (P, ppm) by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).

Figure 7b—Douglas-fir foliar phosphorus (P) concentration (percent) as a function of ash depth (inches), by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedi-mentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).

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


deposits(fig.8b).Sulfate-Savailabilitywasnotaffectedbyash,parentmaterialorvegetationseries.

Douglas-firfoliarBvaluesincreasedwithincreasingashdepth,showinggoodagreementwithsoil-availableBtests(fig.8c).FoliarBwasalsoaffectedbypar-entmaterial,rangingfromabout23ppmongraniticrockstoabout29ppmontertiarysedimentsintheabsenceofash.FoliarCuvalues,incontrast,werenotaffectedbyparentmaterialorashpresenceordepth.FoliarBandCuvaluesweregenerallyabovenutritionalcriticallevels(table2).WhilefoliarSconcentrationswereatorabovecriticallevelmostofthetime,Swasthenextmostlikelyele-ment,afterN,toshowdeficiencylevels.

Figure 8a—Soil available boron (B, ppm) as a function of ash depth (inches).

Figure 8b—Available copper (Cu, ppm) by base parent mate-rial. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), mod-ern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).

Figure 8c—Douglas-fir foliar boron (B) concentration (ppm) as a function of ash depth (inches), by base parent material. Parent materials include basalt, glacial deposit (glacial), gran-ite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).



Fertilization Response

Nitrogen Fertilizer Response—Acrossallgeographicregions,baseparentma-terialsandvegetationseries,6-yeargrossvolumeresponsetoNfertilizerofstandsonash-capsiteswas49.6%greateronaveragethanfertilizerresponseofstandsonnon-ashsites.However,onceashwaspresent,ashdepthhadnoeffect.Thecombinedeffectofparentmaterialandashpresencemoreeffectivelydescribedvariationinresponsethanashcapalone.Ashpresenceincreasedvolumeresponseby87%onglacialdeposits,76%ontertiarysediments,48%onmodernsedimentsand34%onbasalts(fig.9a).Ashpresencedidnotaffectvolumeresponseonmetasedimentaryorgraniticparentmaterials.Vegetationseriesdidnotdescribeanyadditionalfertilizationresponseonceashpresencewasaccountedfor.Amodelcombiningparentmaterialandvegetationserieswasmoreeffectiveatexplain-ingvariationinresponse(fig.9b)thantheparentmaterialandashmodel.SitesonwesternredcedarvegetationseriesandbasaltorglacialtillparentmaterialsshowedthehighestNfertilizerresponse,whilesitesonDouglas-firvegetationseriesandmetasedimentaryparentmaterialsshowedthelowestresponse,withothersitesfallinginbetween.Eventhoughthisrelationshipbetweenresponseandvegetationseriessuggestedthatsoilmoisturemayaffectresponse,therelationshipbetweenvolumeresponsetoNfertilizationandpotentiallyavailablewaterintheupper24inchesofsoilwasstatisticallynonsignificant.

VolumeresponsetoNfertilizerdecreasedwithincreasingsoilmineralizableN(R2=0.34;fig.9c)andammonium-N.However,volumeresponsetoNfertilizershowednorelationshiptounfertilizedfoliarNlevels.ChangesinfoliarNcon-centrationcausedbyNfertilizationwereinverselyrelatedtounfertilizedfoliarNconcentrations(fig.9d).Inotherwords,thelowertheuntreatedfoliarNlevels,thegreaterthechangeinfoliarNresultingfromNfertilization.Neitherashpresencenordepthinfluencedthischange,thusthepresenceofashdidnotappeartoaffecttheavailabilityofappliedNtotrees.Furthermore,neithervegetationseriesnorrocktypeaffectedthefertilization-inducedchangeinfoliarNconcentration.

Figure 9a—Six-year nitrogen (N) fertilization response (ft�ac –1yr –1) by base parent material and ash cap presence. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).



Figure 9d—Change in Douglas-fir foliar nitrogen (N) concentration (percent) following N fertilization as a function of control plot (unfertil-ized) foliar N concentration (percent).

Figure 9b—Six-year nitrogen (N) fertilization response (ft�ac –1yr –1) by base parent material and vegetation series. Parent materials include basalt, glacial deposit (glacial), granite and metasedimentary (metased). Vegetation series include Douglas-fir (DF), grand fir (GF) and western red cedar (WRC).

Figure 9c—Six-year nitrogen (N) fertilization response (ft�ac –1yr –1) as a function of soil mineralizable nitrogen (N, ppm).



Discussion ______________________________________________________

Ash distribution

Ashpresencegenerallyexplainedthesamevariationasgeographicregion,par-entmaterialandvegetationseries.Theconfoundingwithvegetationserieswasnotunexpected.Ithaslongbeenknown,forexample,thatwesternredcedarhabitattypesarehighlylikelytohaveashcap.ItisalsoknownthatashcapismorewidelydistributedinnorthIdaho,northeastWashingtonandnortheastOregonandlesscommonlyfoundincentralWashingtonandcentralIdaho.Theconfoundingofashpresencewithunderlyingparentmaterialtypeisperhapslessintuitive,butislikelyrelatedtothegeographicdistributionofthoseparentmaterials.Siteslocatedontertiarysedimentarydeposits,metasedimentaryrocksandglacialdepositsaremorelikelytooccurinnorthIdahoandnortheastWashington,whilesiteslocatedonbasalts,granites,moderndepositsandsedimentaryrocksaremorelikelytooccurincentralWashingtonandcentralIdaho.

Site Productivity

WhileSIwasavailableforonly110sitesandCGRforall139sites, thetwovariableswerehighlycorrelated(R2=0.59),suggestingthatbothvariablesbehavedsimilarlyasdescriptorsofsiteproductivity.Forbothvariables,ashpresenceatadepthof1inchorgreatersignificantlyincreasedsiteproductivityrelativetonon-ash sites. The increasewasgreater forCGR, suggesting that this variablewasamoresensitiveindicatoroftheeffectofashpresenceonsiteproductivity.However,additionalashdepthhadnoeffectoneitherofthesiteproductivityvariables.Thus,onceashwaspresent,itdidnotappeartomatterhowdeeptheashwasintermsofpredictingsiteproductivity.

Even though potentially available water was positively correlated with ashdepthandsiteproductivity,siteproductivitywasunaffectedbyincreasingashdepth.Thismeantthatsomethingabouttheashbesidespotentiallyavailablewaterwasaffectingsiteproductivity.Decreasednutrientavailabilitywasonepossiblefactorlimitingsiteproductivity.Foliageandsoil-availableMgandCagenerallydecreasedwithincreasingashdepth.Decreasedavailabilityoftheseelementsonsiteswithdeeperashcapscouldhelpexplainthelackofacorrespondingincreaseinsiteproductivityeventhoughpotentiallyavailablewaterwashigheronsuchsites.PositiverelationshipsbetweenashandnutrientavailabilityofB,PandKsuggestedthat theseelementswerenotlikelygrowth-limitinginthepresenceofash.

Site Fertility

Soil Moisture—Potentialavailablewaterisadescriptorofthecapabilityofasitetoretainandsupplymoisturetotheplantsgrowingonthatsite.Potentiallyavailablewaterincreasedwithincreasingashdepth,asseemedreasonablebasedonourexperiencewithash-capsoils.ThefindingthatpotentiallyavailablewaterwasgreateronwesternredcedarseriesthanongrandfirorDouglas-firseriesalso seemed reasonable, given that most western red cedar sites occurred inconjunctionwithash-capsoils.However,variationinpotentiallyavailablewaterbyvegetationseriesandashdepth(fig.3b)suggestedthatsitesonwesternred



cedarvegetationseriesstillhadhigheravailablewaterthansitesongrandfirorDouglas-fir series evenafter accounting for ash.Thus, somethingbesides ashpresenceanddepthaffectedpotentiallyavailablewaterandtheresultingvegeta-tionseries.Factorsbesidesashlikelytoaffectsoilmoistureandvegetationseriesareclimate,soiltemperatureregime,soildepth,soiltexture,parentmaterialandtopographicposition(slope,aspect,andelevation).

Someofthevariationinpotentiallyavailablewateramongparentmaterialsinthepresenceofashlikelyreflecteddifferencesinunderlyingsoiltextureaswellasashdepth.Basaltandmetasedimentaryrocksweathertofinersize-classsoilswithinherentlyhigherpotentialmoistureavailabilitycomparedtothecoarser-grainedandmorepermeable soilsderived fromgranitic rocksandglacialde-posits.However,theinteractionbetweenashpresenceandparentmaterialwaslesseasilyexplained.Sitesongraniticrocksandglacialdepositsshowedhighermoistureavailabilityintheabsenceofashthaninthepresenceofashallowashlayer(fig.3c).Sitesongraniticrocksneededabout7inchesofashandglacialsitesabout16inchesofashtoachievethesamepotentiallyavailablemoistureasthenon-ashsitesonthesesamerocktypes.Aftermeetingthesethresholdlevels,potentiallyavailablemoisturecontinuedtoincreasewithincreasingashdepthonbothrocktypes.Perhapssomedegreeofsoilmixingoccurredbetweenashandtheunderlyingresidualsoilsthatnegativelyimpactedmoisture-holdingcapacityattheshallowerashdepths.

Soil Acidity—SoilpHtendedtoincreasewithincreasingashdepth.However,acomplexrelationshipbetweenparentmaterialandashdepthsuggeststhatthisincreasewasdrivenprimarilybydatafromsitesongraniticandbasalticsubstrates,whereincreasingashdepthledtoincreasedpH.Onallotherparentmaterials,whichweresedimentaryinorigin,ashdepthhadnoeffectonsoilpH.Therea-sonsforthisbehaviorarenotentirelyclear.SoilpHlevelsoftheresearchsitesincludedinthisstudywerewithinarangewherenutrientavailabilityanduptakeofappliedfertilizerelementsshouldnotbeadverselyaffected.

Nitrogen—FoliarandsoilmeasuresofNavailabilitysuggestedthatNwasaffectedbyparentmaterial,butunaffectedbyashpresenceordepth.Soilmineraliz-ableNandavailableammonium-Nwereconsistentlyhigheronmetasedimentaryandtertiarydepositsitesandlowerongraniticandbasalticsites.Incontrast,foliaranalysessuggestedthatNuptakewasgreatestonsiteswithbasaltparentmaterials.Thissuggeststhattreesgrowingonbasaltparentmaterialswerebet-terabletotakeadvantageofsoil-availableNthantreesonotherrocktypes,orconverselythattreesonmetasedimentaryandtertiarysedimentarydepositswerelessabletoutilizesoil-availableN.

Reasonsforthecontrastingeffectsofparentmaterialonsoil-availableNpoolswerenotclearfromthisanalysis.ParentmaterialcouldpositivelyaffectNsupplybyimpartingsoiltexturalorchemicalconditionsthatareconducivetoincreasedN-mineralizationrates.Conversely,parentmaterialmaynegativelyaffectplantuptakeofNthroughintroductionofamoresignificantgrowth-limitingfactor,suchaslowmoistureavailability(affectedbysoiltexture)orlownutrientavailability(affectedbyparentmaterialmineralogy).EitherscenariocouldcontributetoanincreaseinthesoilmineralizableNpool.MineralizableNwasstronglycorrelatedwithsoilorganicmatterandsoilcarbon,suggestingthatN-mineralizationrateswerealsogovernedbyorganicmatteravailability.Climaticconditionsmayaffectorganicmatterproductionbyaffectingproductivityand/orbyaffectingconditions



conducivetoNmineralization.WhilefoliarNwasonlyweaklycorrelatedwithmineralizableN,itwasnegativelycorrelatedwithelevation,suggestinggreaterNavailabilityonwarmer,lowerelevationsites.Othersitefactorsincludingsitefertility,soilwaterpotentialandtopographicfactorshadnoeffectonfoliageNconcentrations.

Cations—LikeN,cationswerealsoaffectedbybaseparentmaterials,thoughinamorepredictablefashion.Intheabsenceofash,soil-extractableCaandMgconcentrationsintheupper12inchesofsoilwerehigheronbasaltparentmaterialsandlowerongranites.BecausebasaltsarehigherinCa-andMg-bearingmineralsthangranites,thisfindingisplausible.However,onceashwaspresent,availableCaandMgdecreasedwithincreasingashdepthonbothbasaltsandgranites.ThissuggeststhatCaandMgstorageinashispooreveninthepresenceofCa-andMg-richunderlyingparentmaterials,andthatsoilCaandMgavailabilitymaybeloweronsiteswithdeeperashcaps.Thismayreflectthedilutionofresidualsoilswithincreasingashpresence,andaresultingdilutionofCaandMgpoolsintheupper12inchesofsoil.Foliarchemistryalsosuggestedthatplantuptakeofbothelementsdecreasedatincreasingashdepths.

IncontrasttoCaandMg,soil-extractableKwasunaffectedbyashpresenceordepth,andwasonlyaffectedbyparentmaterial.Theparentmaterialeffectwasdrivenbybasalt,whichshowedhigherextractableKthanotherrocktypes.However,foliarKwasunrelatedtoparentmaterial,andwaspositivelyaffectedbyashpresence(butnotaffectedbydepth).Thelackofarelationshipbetweensoil-extractableKandfoliarKcouldindicatethateitherthesoilorfoliartestforKwasinadequate.TheseresultscouldalsosuggestthatashpresencesomehowfacilitatedtreeuptakeofK,eventhoughsoil-extractableKappearedunaffectedbyashpresence.ThismayalsobeanindicatoroflowcationretentionbyashsoilsandthehighmobilityoftheK+ion.

Phosphorus—DespiteconcernsofpossiblePadsorptionbyashsoils,soilandfoliartestssuggestedthatPavailabilityanduptakewereunaffectedbyashpresenceordepth.Onallsites,foliarPconcentrationswereatorabovenutritionalcriticallevels,suggestingthatsufficientPwasavailablefortreegrowthandfunction.

Boron, Cu and S—Boronshowedincreasingsoilavailabilityandfoliarconcen-trationwithincreasingashdepth.ThispositiverelationshipsuggeststhatashmayprovideefficientstorageforB,andalsothatashdoesnotadsorbBtoanextentthatmakestheBunavailableforplantuptake.AshdidnotaffectsoilorfoliarCuvalues.Soil-availableCushowedsomevariationbyparentmaterialthatwaslikelyrelatedtotracemineralsinthevariousparentmaterials.However,therewaspooragreementbetweensoil-availableandfoliarCuconcentrationsinthatfoliarCushowednocorrespondingparentmaterialeffect.Soil-availableSwasunaffectedbyashpresenceordepth,orbyparentmaterial.

Fertilization Response

Nitrogen—Overall,volumegrowthresponsetoNfertilizationwasmuchbetteronsiteswithashthanonsiteswithout.IncludingbaseparentmaterialinthemodelwithashcontributedanadditionaldegreeofpredictabilityofvolumeresponsetoNfertilization.Ashwasparticularlyvaluableinincreasingfertilizationresponseonthesedimentarydeposits(includingglacialdeposits)andsomewhatlesssoonthebasalt,graniteandmetasedimentaryrocks.



TherelationshipoffertilizationresponsetosoilmineralizableNsuggestedthatthelowerthemineralizableN,thehigherthefertilizationresponse.Thissupportsthe idea thatN-deficient sites should showahigherdegreeof response toNfertilization.Similarly,thechangeinfoliarNconcentrationfollowingfertilizationshould indicate theeffectivenessof the fertilization treatment inchanging theamountofNavailabletothetreesforgrowth.However,unfertilizedfoliarNcon-centrations,whileinverselyproportionaltothechangeinfoliarNconcentrationfollowingNapplication,didnotshowanyrelationshiptofertilizationresponse.Thus,whilelowerfoliarNlevelswerepredictiveofagreaterincreaseinfoliarNafterfertilization,theywerenotnecessarilypredictiveofagreaterNfertilizationresponse.IncreasesinfoliarbiomassfollowingNfertilizationhavebeenshowntobemorepredictiveoffuturevolumeresponsethanchangesinNconcentrationalone(WeetmanandFournier1986;HasseandRose1995;Brockley2000).

Sulfur and K—SiteswithashgenerallyrespondedbettertoSfertilizationthanthosewithout.However,onceashwaspresent,thetrendwasdecreasingresponsewithincreasingashdepth,suggestingpossibleSadsorptionbyash-capsoils.Noevidencewas foundtosuggest thatashpresenceaffectedgrowthresponseorfoliarKstatusfollowingKfertilization.

Nutritional Characteristics of Ash

Anionadsorptionmaybeanissueofconcerninashsoilsduetothecharacter-isticvariablechargeofash(McDanielandothers2005;Kimseyandothers2005).ThedecreaseintreegrowthresponsetoSfertilizationwithincreasingashdepthsuggestspossiblesulfateretentionbyashsoils.HowevernoevidenceofnitrateretentionappearedfollowingNapplicationasureaorammonium.Foliar testssuggestedthatappliedNwastakenupbythetrees,and6-yeargrowthresponsesuggeststhatN-fertilizationdidincreasebiomassandvolumeproduction.Phos-phorusandBwerenotappliedduring these fertilization trialsbecause foliagetestsindicatedthattheseelementswerenotdeficient.Ourresultsalsosuggestedthatashdidnothaveanyeffectonsoil-availableorfoliarP,implyingthatPisnotlikelyagrowth-limitingelementonash-capsoils.Boronavailabilityappearedtoincreasewithincreasingashdepthaccordingtobothsoil-availableandfoliagetests.WhileinsufficientdatawereavailabletotestforthefateofBfollowingap-plication,Badsorptiondidnotseemtobeagrowth-limitingcharacteristicofashsoilsduringthisanalysis.

Theinabilityofpure,unweatheredashtostoreandsupplycationsmayalsobeanissueofconcerninandicsoils(McDanielandothers2005).Despitethedegreeofmixingandweatheringexhibitedbytheash-capsoilsinourstudy,storageandsupplymaystillhavebeenanissueforMg2+andCa2+.Bothelementsshoweddecreasedsoilavailabilityandfoliarconcentrationwithincreasingashdepth.ThisoccurredevenwhentheunderlyingparentmaterialswerehighinCaandMg,suggestingpossibledilutionofresidualsoilnutrientpoolsbyash.Incontrast,soil-extractableKwasunaffectedbyashpresenceordepth,andwasonlyaffectedbyparentmate-rial.Thus,ashsoilsappearedcapableoftakingontheKcharacteristicofunderlyingparentmaterial,butnottheCaorMgcharacteristic.ThiscouldoccurbecauseK+isamoremobileionandislikelytobetakenupbyplantsanddepositedonthesoilsurface.Also,foliarKwaspositivelyaffectedbyashpresence,suggestingthatashsoilswerebetterabletosupplyK,thoughnotnecessarilystoreit,comparedtonon-ashsoils.Thus,cationstorageandsupplyornutrientpooldilutionofthe



divalentcationsappearedpotentiallyproblematicinashsoils,whilethemonovalentKionwaslessaffectedbyashretentionanddilutionissues.

Management Recommendations _________________________________Site Nutrition and Nutrient Management

“Nutrient management” refers to silvicultural activities as they affect thenutrientcapitalofaforeststand.Itcanincludefertilizationtreatmentsandac-tivitiesthatretainnutrientsonsiteduringsilviculturalactivities.Becausemostnutrientsareheldinlimbsandfoliage(Coleandothers1967;Pangandothers1987;Millerandothers1993;Moller2000),aconservativenutrientmanage-mentstrategywouldbetoleavethetopsandlimbsofharvestedtreeson-sitethroughavarietyofbole-onlyharvestingtechniques.Whole-treeoperationsinlatefallandwinter,whenbreakageismorelikely,shouldalsobeeffectiveatretainingsomenutrientsonthesite.Speciesdifferinnutrientdemand(Gordon1983;Gowerandothers1993;Millerandothers1993;Mooreandothers2004).Therefore,plantingnutritionallychallengedsiteswithless-demandingspeciesand favoring less-demanding species during silvicultural operations are alsoconservativenutrientmanagementstrategies.

Testsoffoliageandsoilchemistrymaybeperformedassitespecificindicatorsofproductivityandpotentialfertilizationresponse.FoliarNwasabetterpredictorofsiteproductivity,whilesoilmineralizableNwasabetterpredictoroffertilizerresponse.Ifsatisfactoryinformationonsiteproductivityisavailableandtheparentmaterial/ashcombinationsuggeststhatthesitemayberesponsivetofertilization,managersshouldconsiderfocusingontestsofsoilmineralizableN.Ifmineraliz-ableNisbelow70ppm,thesiteshouldshowa6-yearvolumeresponseof10%ormore,withthepotentialresponseincreasingasmineralizableNdecreases.FoliarNmaybetestedasanindicatorofoverallsiteproductivity;however,theeffortandexpenseofthistestmakeitlessdesirablethanperformingsimplesiteheight/agemeasurements.

Nutrient Management Recommendations by Parent Material and Ash Presence

Basalts, Glacial and Modern Deposits—Sitesonbasalts,glacialdepositsandmodern sedimentarydeposits showednochange in siteproductivity in termsofCGRinthepresenceofash.Howeverthesesitesdidshowmoderate(basaltandmodernsedimentary)tohigh(glacialdeposit)increasesinvolumegrowthresponsestoNfertilizationwhenashwaspresent.ThissuggeststhatsitesontheseparentmaterialsshouldrespondreasonablywelltoNfertilizationwithoutash,andrespondevenbetterwhenashispresent.Therewasweakevidencethatonbasaltparentmaterials,thepresenceofashinhibitedvolumeresponsetoSfertiliza-tion.However,otherIFTNCstudieshaveshownthatSissometimesnecessarytostimulateagrowthresponsetoNfertilizationonbasaltparentmaterials(Garrisonandothers2000).WhileallparentmaterialsinthiscategoryshouldrespondwelltofertilizationwithNonly,strongergrowthresponsesmightbeinducedbymulti-nutrientfertilizationthatincludesS.Conservativenutrientmanagementstrategiesshouldbeevaluated,butmaybelesscrucialontheseparentmaterialscomparedtootherparentmaterials.



Metasedimentary and Granite—Metasedimentaryparentmaterials showedrelatively lower site productivity and granites showed moderate productivitycomparedtootherparentmaterials.Siteproductivityincreasedinthepresenceofashonbothparentmaterialtypes,withmetasedimentaryproductivitydoublingintermsofCGR.However,N-fertilizerresponsewasunaffectedbyashpresenceforeitherparentmaterial.Thissuggeststhat(1)treesgrowbetteronmetasedimentaryandgraniticrockswhenashispresent,and(2)fertilizationwithNalonewillnotincreaseproductivityonashsitesoverthatofnon-ashsitesonmetasedimentaryorgraniticrocks.TherewasweakevidencethatmetasedimentaryandgraniticsiteswithashmayrespondpositivelytoSfertilization.Preliminaryresultsofre-centfertilizationscreeningtrialsonbothparentmaterialtypesshowedgenerallypoorgrowthresponsetofertilizationwithNalone,andstrongerresponsetoacombinedtreatmentofN,K,S,andBwhenashwaspresent(Garrison-Johnstonandothers2005,unpublisheddata).Thus,multinutrientfertilizationismorelikelytostimulategrowthresponseonashsoilsonmetasedimentaryandgraniticparentmaterials.Generalnutritionalchallengesofthesesitessuggestuseofconservativenutrientmanagementstrategies.

Tertiary Sedimentary Deposits—Tertiarysedimentaryparentmaterialsbehavedsomewhatdifferentlythantheotherparentmaterialsinthatbothsiteproductiv-ityandNfertilizationresponsewereenhancedinthepresenceofash.Becausetheavailabledatafortertiarysedimentarysiteswassparse,theseresultsforthisdeposittypeshouldbeviewedcautiously.However,thissuggeststhatifstandsontertiarysedimentsaregrowingwell,theyshouldrespondwelltoNfertilizationintheabsenceofash,andevenbetterwhenashispresent.Somecautionshouldbeexercisedinapplyingfertilizer,however,asfieldexperiencehasalsoshownthattertiarysedimentarydepositscaninherentlybequitevariableincomposition.Pendingfurtherinvestigation,useofconservativenutrientmanagementstrategiesisalsorecommended.

Conclusions _____________________________________________________Standproductivitywasgreateronsiteswithashcapthanonsiteswithout;how-

everonceashwaspresent,changesinashdepthdidnotaffectsiteproductivity.Becauseashpresenceorabsencetendedtocoincidewithparticularvegetationseriesandgeographicregions,ashpresencedidnotfurtherexplainvariationinsiteproductivitybeyondthatdescribedbythosevariables.Whileashpresencealsotendedtocoincidewithparticularparentmaterialtypes,ashpresencestillexplainedsomevariation insiteproductivitybeyond thatexplainedbyparentmaterial.Ashpresencewasmostlikelytoincreasesiteproductivityonmetasedi-mentaryrocks,granitesandperhapstertiarysediments.

Althoughsiteproductivitywaspositivelycorrelatedwithpotentiallyavailablewaterandpotentiallyavailablewaterwaspositivelycorrelatedwithashdepth,therewasnocorrelationbetweensiteproductivityandashdepth.Thissuggeststhatsomethingelseabouttheash,suchaspoornutrition,affectedproductivity.Soil-availableandfoliarMgandCadecreasedwithincreasingashdepth.Thus,whileincreasingashdepthmayhaveapositiveeffectonsoilmoisturepotential,itmayhaveanegativeeffectonnutrientavailability,particularlyforMgandCa,andthereforeonsiteproductivity.



SoilNavailability (mineralizableandammonium)and foliageNconcentra-tionswerenotaffectedbyashpresenceordepth,butwereaffectedbyparentmaterial.Reasonsfortheparentmaterialeffectwerenotentirelyclear,howeverthesiteproductivityandsoil texturalandchemicalconditionsassociatedwithparticularunderlyingparentmaterialslikelyaffectedorganicmatterproductionandcycling.SoilorganicmatterandcarboncontentwerehighlycorrelatedwithsoilNavailability.ClimateandelevationlikelyinteractedwithparentmaterialstohaveaneffectonNavailability,aswell.

Possiblenutrientadsorptionandsupplybyashwerealsoconsidered.AdsorptionofappliedNdidnotappeartooccurinash-capsoilsinthisstudy.Incontrast,decreasing growth response to S-fertilization at greater ash depths suggestedthatadsorptionofappliedSmayhaveoccurred.Foliageandsoil-availabilityofPandBeithershowednochange(P)orincreasedavailability(B)withincreasingashdepth,suggestingthatavailabilityoftheseelementsmaynotbeanissueofconcerninash-capsoils.LackofsoilMgandCastorageandsupplyatgreaterashdepths,orperhapsdilutionofMgandCasupplybyincreasingquantitiesofash,didappeartooccur.SoilKwasunaffectedbyashpresenceordepth,whilefoliarKconcentrationsincreasedwhenashwaspresent,suggestingthatKsupplywasperhapsenhancedbyashpresence.

Averagevolumeresponse toN fertilizationwasalmost50%greateronashcomparedtonon-ashsites.Howeverchangesinashdepthdidnotfurtheraffectvolumeresponse.AshpresenceincreasedvolumeresponsetoNfertilizationonglacialdeposits, tertiarysediments,modernsedimentsandbasalts,butnotongraniteormetasedimentaryparentmaterials.Volumeresponsewasgreatestonwesternredcedarvegetationseries,followedbygrandfirandthenDouglas-firvegetationseries.Howeverashpresenceordepthdidnotfurtheraffectvolumeresponseoncevegetationserieswasknown.Parentmaterialcombinedwithveg-etationseriesbestdescribedvolumeresponsetoN-fertilization.

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