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97USDA Forest Service Proceedings RMRS-P-44. 2007

The Practice of Sustainable Soil Management

Sustainablesoilmanagementcanbedefinedasensuringthebiological,chemicalandphysi-cal integrityof the soil remains for futuregenerations. Sustainability shouldbeaddressedthroughoutallfacetsofforestmanagementincludingimplementationofindividualharvestorstand-tendingplans,developmentofagencyorcompanystandardsandbestmanagementpractices(BMPs),andthird-partycertification.Demonstrationofsustainablesoilmanagement

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.

Mike Curran, Corresponding author, Research Soil Scientist, B.C. Ministry of Forests and Range, Forest Sciences Pro-gram, Kootenay Lake Forestry Centre, Nelson B.C., Canada. (also Adjunct Professor, Agroecology, University of B.C.). Pat Green, Forest Ecologist, Nez Perce National Forest, Grangeville, Idaho. Doug Maynard, Research Scientist, Natural Resources Canada, Canadian Forest Service, Victoria BC, Canada.

Abstract Sustainabilityprotocolsrecognizeforestsoildisturbanceasanimportantissueatnationalandinternationallevels.Atregional levelscontinualmonitoringandtestingofstandards,practices,andeffectsarenecessary forsuccessfulimplementationofsustainablesoilmanagement.Volcanicash-capsoilsareaffectedbysoildisturbanceandchangestosoilpropertiesinfluenceecosystemresponsessuchasproductivityandhydrologicfunction.Soildisturbancefromtimberharvesting,reforestation,orstandtendingismainlyaresultofmovingequipmentandtrees.Compactionandorganicmatterremovalareofprimaryconcern.Theseverityandextentofdisturbancedependontheharvestsystem,soil andclimaticconditions.Ash-cap soilscanbe susceptible todisturbanceand schemes topredictcompaction,displacementanderosionhazardsareusefulforplanningforestmanagementoperations.On-siteeffectsrangefrompermanentlossofgrowingsitesbecauseofroads,tomoresubtlechangesinsoilpropertiesthatultimatelyinfluencesiteproductivity.Off-siteeffectsmay includeerosionand landslides.Soildisturbanceduringoperationsshouldberegulatedandmonitoredtominimizebothon-andoff-siteeffects,whichcantakeyearsordecadestoappear.Foresthealthissuesvaryonvolcanicash-capsoils.AnanalysisofArmillariarootdiseaseincidenceacrosstheNationalFor-estsoftheInlandNorthwestindicatessomepotentialrelationshipsamongrootdisease,andsoilandsitefactors.Thestrongrelationsbetweenpresenceofsusceptiblehostanddevelopmentoffungalbiomassmaybethestrongestcausalagent,withthesoilandsitefactorssupportingthepresenceofthepathogenandsusceptiblehost.Thickerashsoilsofmorenortherlyareasarerelatedtohabitattypesthathistoricallysupportedwhitepineandahigherdiversityoflesssusceptiblespecies.Afterrootdiseasemortalityoccurs,thesemoremesicenvironmentsalsofillinwithotherspeciesrapidly,sohigherlevelsofrootdiseasearemoredifficulttodiscern.Recommendationsaremadeforsoilmanagementandaboutinformationneedsforsoildisturbanceandrootdiseaserelations.

Key words:volcanicash-capsoils,foresthealth,Armillaria,rootdisease,criteriaandindicators,organicmatterdeple-tion,soildisturbance,soilcompaction,sustainabilityprotocols

Volcanic Ash Soils: Sustainable Soil Management Practices, With Examples of Harvest Effects and Root Disease Trends

Mike Curran, Pat Green and Doug Maynard

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ispromoted through reportingprocedures requiredbyapplicable sustainabilityprotocols,andbyhavingthird-partycertificationofforestpracticesandproducts(Curranandothers2005a).

Sustainabilityprotocolsexistatinternationalandnationallevels.Attheinter-nationallevel,theMontrealProcess(MP)includesaWorkingGrouponCriteriaandIndicatorsfortheConservationandSustainableManagementofTemperateand Boreal Forests (Montreal Process Working Group 1997). Some countrieshavedevelopedtheirownprotocolsandproceduresdesignedtotrackandreportprogresstowardmeetingrequirementsofinternationalprotocolssuchastheMP.Forexample,theCanadianCouncilofForestMinistersrecentlydevelopedrevisedcriteriaandindicatorsforsustainableforestmanagement(CCFM2003).

Third-party(eco)certificationofforestpracticesandresultingwoodproductsaroseinresponsetosustainabilityprotocolsandthegreeningoftheglobalmarket-place.OrganizationssuchasSustainableForestryInitiative(AmericanForestandPaperAssociation),CanadianStandardsAssociation,ForestStewardshipCouncil(FSC),andISO1400.1allhavedocumentedreviewprocessesandproceduresforcertification.Protectingstreamsandnaturaldrainagepatterns,maintainingslopestability,and regulating soildisturbancearecommonelementsconsidered. Inaddition,mostrequiresomeadaptivemanagementprocesstoensurecontinuousimprovementofpracticesontheground.Compliancewithcurrentsoildisturbancestandardsisoftenusedasaproxyforensuringsustainability;however,acommonapproachtostandards,andvalidationofthestandardsthroughresearchareim-portantstepsthatmustnotbeoverlookedwhentheseareusedasproxies.Somecertificationschemesalsocallformorerestrictivestandards(e.g.,FSCinBritishColumbiacallsforlowerdisturbancelevelsthanProvincialregulations).

Atthelocallevel,whenmanagingharvest-effectsonsoils,treegrowthandlong-termproductivity,soildisturbancefrommechanicaloperationsisofmostconcern.Soildisturbanceoccurringattimeofoperationscanhavenegative,positive,ornodetectableeffectongrowthorhydrologicfunction.Soildisturbanceatthetimeofoperationsisoftenanindicatorusedinregulatinglong-termproductivityandhydrologiceffects.ThisisbecauseinmanyNAecosystems,weneedatleast10to20yearsdatatodrawconclusionsabouttheeffectsofvariouspracticesongrowthorhydrologicfunction.Indiscussingevidenceforlong-termproductivitychanges,MorrisandMiller(1994)indicatedslow-growingstandsrequire20ormoreyearsofgrowthbeforelong-termproductivityconsequencescanbeascer-tained.Soildisturbanceistheproxythatwecanobserveandregulateatthetimeofharvestingandsitepreparation.However,thisproxyalsoneedstobevalidatedandrevisedovertimeinanadaptivemanagementprocessthatincludesstandards,bestmanagementpractices,monitoring(compliance,effectivenessandvalidation),furtherresearchandstrategicdirectionandrevisionovertime(Curranandothers2005b).Acommonapproachisneededfordescribingsoildisturbancesothatresultsachievedindifferentareasarecomparable(Curranandothers2005c).

Management and Communication Frameworks for Sustainable Soil Management _______________________________________________

Justlikeecosystemclassificationschemes(e.g.,BraumandlandCurran1992)inneighboringBC,organizingsoilintomappableorotherwisedescribableunitsprovidesanimportantframeworkforcommunicatingmanagementexperience,

Curran, Green, and Maynard Volcanic Ash Soils: Sustainable Soil Management Practices, With Examples of Harvest Effects and Root Disease Trends

researchresults,andconservationefforts.Detailedsoilor landtypemapsareavailableformuchoftheash-capsoilsintheUnitedStates,andreconnaissance-levelsoilmappingisavailableinsouthernBC.Mapsdesignatesoilunits(e.g.,soilseriesindetailedmappingandsoilorlandtypeassociationsinreconnaissancemapping)basedonsoil-formingfactorsofparentmaterial,topography,climateandvegetation,allactingovertime,whichvariesduetogeologiceventslikeglaciationandvolcaniceruptions.Asdiscussedabove,soildisturbancecanalsobeclassifiedandweareworkingtowardsacommonclassificationthereaswell.

Perhapsthemostusefulwayoforganizingsoilunitsforforestmanagementisaconsiderationoftheirriskofdamagefromsoildisturbance.Themostcommondisturbanceofconcerninforestmanagementisfrommachinetrafficduringhar-vesting,sitepreparation,orfuelmanagementtreatments.Thebiggestconcernsassociatedwithmachinetrafficaresoilcompaction,soildisplacement,andsoilerosion.Inaddition,slopestabilityisaconcernonsteeperandwettersites.Toidentifyandmitigatethepotentialforlandslides,terrainmappingand/orterrainstabilityfieldassessmentsareusedonsitesthatexceedcertainslopegradientsorhaveindicatorsofpotentialslopeinstability.

Determiningthesoildisturbancehazardsonagivensiteprovidesaframeworkfordevelopingharvestingstrategiesbyalertingtheprescriptiondevelopertothespecificsoildisturbanceconcernsonthatsite.Forexample,inBC,soildistur-bancedefaultstandardsundertheForestandRangePracticesAct(FRPA)permitup to5or10%netdisturbancewithinacutblockarea (excludingpermanentaccess).IntheInterior,thetriggerfor5%iswhenoneofthekeyhazardsisVeryHigh.AHighratingforanyhazardisprimarilyintendedtoalerttheprescriptiondeveloperandtheoperationalstaffofahazardthatmayrequirespecialtreatmenttopreventproblems(manageandmitigatethehazard).Highcompactionhazardalsoresultsinmoreequipmenttrafficdisturbancetypesbeing“counted”1underFRPAdisturbancecriteria. The soil disturbancehazards alsohelp identify siteconditionsthataresuitableforconstructionofexcavatedandbladedtrails(skidroadsorbackspartrails),and/ortemporarilyexceedingsoildisturbancelevelsandrehabilitatingslopehydrologyandforestsiteproductivity.Thehazardsaredefinedbelow,includingbriefdiscussionsofwhytheyareofconcern.2

Soil Compaction Hazard

Soilcompactionistheincreaseinsoilbulkdensitythatresultsfromtherear-rangementofsoilparticlesinresponsetoappliedexternalforces.Soilpuddlingisthedestructionofsoilstructureandtheassociatedlossofmacroporositythat

1InBC,theterm“counted”isusedinreferencetosoildisturbancetorecognizethefactthatsoildisturbancetypesortheirseverityvarywithsoilsensitivitytodisturbance.Moredisturbancetypesareofconcernonmoresensitivesoils,andlessareofconcernonmoreresilientsoils(e.g.,sandysoils).Thenetresultisthatmoredisturbancetypesare“counted”towardsthetotalcumula-tiveallowablelimitonmoresensitivesoils.

2Soildegradationhazardratingkeysforsoilcompaction,displacement,anderosionarefoundinLandManagementHandbook47(Curranetal.2000)andtheForest Practices Code of British Columbia, Hazard Assessment Keys for Evaluating Site Sensitivity to Soil Degrading Processes Guidebook.The general BCMOF Web site where these and other FPC information can be lo-cated is: http://www.for.gov.bc.ca/ (look under legislation).

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results fromworking the soilwhenwet.Organicmatter isoften incorporatedduringpuddlingandbecauseorganicmatterislighterthanmineralparticles,soilbulkdensitymaynotincrease;however,theotherpropertiesdescribedbelowarestillnegativelyaffected.ThescienceandrationalefortheBCcompactionhazardkeyarelaidoutinCarrandothers(1991).

Soilmoisturecontentisprobablythebestdeterminantofcompactionhazardatanygiventime.InBritishColumbia,thesoilcompactionhazardkeyranksthepotentialcompactionhazardbygroupingsoiltexturesthataremostsusceptibletostructuraldegradationfromcompactionandpuddling,andaremostlikelytoholdmoistureandremainwetforlongerperiods.Thesoilcompactionhazardkeyisatooltohelpwithplanningofanoperation,whilecarefulmonitoringofequipmenteffectsonthesoil,andhandtestsforsoilmoisturecontentarethetoolsthathelpguidetheoperation.

Soilcompactionandpuddlingareofconcernintimberharvestingoperationsbecauseofeffectsonrootsandsitewaterrelations.Compactedsoilshavehigherpenetration resistance thatcan impede rootgrowth.Compactedandpuddledsoils bothhave lower aerationporosity and lowerhydraulic conductivity andinfiltrationrates;however,insomecoarsertexturedsoils,compactionmayactu-allyincreasewaterholdingcapacity(thesesoilstypicallyhavelowercompactionhazardratings).

Loweraerationporosity results in reducedgasexchange thatcanadverselyaffectoxygen levels in the soil air; this reducesphysiologic functionof roots,whichinturncanleadtorootdieoffunderwetterconditions.Lowerhydraulicconductivityandinfiltrationratesofthecompactedorpuddledsoilcanresultinincreasedrunoffduringrainfallandsnowmeltevents.Thiscanleadtoincreasednetexportofwaterfromacutblock,whichcanaffectdownslopesites,naturaldrainagefeatures,andotherresourcevaluesduetoerosionandsedimentation.Increasedwaterexportalsomeanslesswatermaybestoredonsitetosupporttreegrowthduring summerdrought.Compacted soils canalso remainwetterlonger,therebyfurtheraffectingseedlingsbecausethesoilmaybecolderandhavepooraeration.

Monitoringoftraditionalspringharvestingonthreeash-capinfluencedsoilsinthesouthernRockyMountainTrenchnearCranbrookindicatedthatsignificantdeclinesinaerationporosityoccuredwhenevidenceofequipmenttrafficwasvisibleontheground(e.g.,wheellugmarksonthesoilorslightimpressionswithtrackgrousermarks) (Utzigandothers1992).Thesesiteswere typicalTrenchsoils:siltloamtosiltyclayloamtexturedsurfacesoilslowincoarsefragments,underlainbydensersubsoilswithmorecoarsefragments.

TheundisturbedsoilshadaerationporosityvaluesatorabovethethresholdrecommendedbytheUnitedStatesForestService(USFS)insomeofitspolicyforthePacificNorthwest(i.e.,15%at10J/kgwatertensionreferredtoinBoyer1979). Regardless of the severity of disturbance, aeration porosities were lessthan15% (fig.1). Effectson saturatedhydraulic conductivity (i.e.,water rela-tions)weresimilar(fig.2).Bulkdensityincreasedinasimilarbutoppositetrendtotheaerationporosityandsaturatedconductivity,aswouldbeexpected.Theconcernabouttheseeffectsishowextensivethemachinetrafficdisturbanceisonfullymechanizedharvesting.Onthethreesitesstudied,thecombinedtotalofthelightruts,5-cmruts,andmaintraildisturbancerangedfrom52to64%oftheentirecutblockarea,withlightermachinedisturbancecoveringfromabout30toover45%(fig.3).

Figure 1—Aeration porosity at 10 J/kg tension for two sample depths at three sites in the southern Rocky Mountain Trench near Cranbrook, BC (Utzig and others 1992). U (undisturbed), VL (very light ruts, <� cm deep), 1 (ruts � cm or deeper), HT (heavy [main] trails).

Figure 2—Saturated hydraulic conductivity for two sample depths at three sites in the southern Rocky Mountain Trench near Cranbrook, BC (Utzig and others 1992). U (undisturbed), VL (very light ruts, <� cm deep), 1 (ruts � cm or deeper), HT (heavy [main] trails), from Curran (1999).

TheseresultsareconsistentwithmonitoringstudiesofnearbysitesinnorthernWashington,Idaho,andMontana(Kuennenandothers1979;LaingandHowes1988,Svalberg1979). In theWashington study,basedon the literatureat thetime,LaingandHowes(1988)predicteda“conservativeestimateof35%volumereductionsoverthenextrotation”fordetrimentallycompactedareas(42%ofthecutblockareaintheirstudy).OnsimilarsitesinNorthernIdahoandMontana,Kuennenandothers (1979) suggested that changes in soil physicalpropertiesresultingfromcompactioncandecreasetheabilityoftreestocompetewithpinegrass.Itisnotclearwhetherthesetypeofeffectswouldberealizedonoursoils;however,intheabsenceoflong-termdatatothecontrary,weneedtocontinuetomonitortreegrowthonthesesites.LightcompactionisalsobeingstudiedaspartoftheNorthAmericanLong-termSoilProductivityStudy(LTSP).

Insummary, the implications forsitewaterstorage, runoff,and treegrowthareofconcernwhenrandomskiddingcausesthesetypesofdisturbances.Itisthereforeinferredthat,undercertainsoilconditions(e.g.,harvestingunderwetterthanoptimumsoilconditions),detrimentalcompactioncanoccurbeforesoildis-turbancecriteriaforrutsortrailsarereached.Harvestingstrategiesrecommendingdispersedskiddingtrafficneedtorecognizethisriskand“treadlightly.”Compac-tionisalong-livedphenomenon;naturalfreeze-thawandwet-drycycleshave

Figure 3—Aerial extent of soil disturbance at three sites in the southern Rocky Mountain Trench near Cranbrook, BC (Utzig and others 1992). LL (very light ruts, <� cm deep), HL (heavy [main] trails), 1&2 (ruts � cm or deeper), and L (very light and heavy, combined) from Curran (1999).

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notbeenobservedtoamelioratemachine-inducedcompactionatdepth.Intheash-capsoillocations,wheresummerdroughtisoneofthefactorsmostlimitingtotreegrowth,andintheabsenceoflong-termdatatothecontrary,preventionofwidespread“belowtheFRPAdepthlimit”compactionisprobablythebestbetandcanbeachievedeconomically.

Soil Displacement Hazard

Soildisplacementisthemechanicalmovementofsoilmaterialsbyequipmentandmovementoflogs.Itinvolvesexcavation,scalping,exposureofunderlyingmaterials,andburialoffertilesurfacesoils.Threeaspectsofdisplacementcanproducesoildegradation:

• Exposureofunfavourablesubsoils,suchasdenseparentmaterial,gravellysubsoil,andcalcareous(highpH)soils.

• Redistributionandlossofnutrients. • Alterationofslopehydrology,whichcanleadtohydrologiceffects(discussed

undercompaction,above).

SoildevelopmentisoftenshallowandmanyofthenutrientsthatarelimitingtotreegrowthareoftenbiocycledandconcentratedintheuppersoilhorizonsthroughouttheBritishColumbiaInterior.Asimilaraffectoccursonshallowash-cap soils that overlay less fertile subsoils.Most of the soil nutrients areoftenconcentratedintheforestfloorandtop20cmofmineralsoil(table1).Therefore,wedon’twanttodisplacethisfertiletopsoilawayfromseedlings,orreducetherootingvolumeofthesevitaltopsoillayers.

Table 1—Typical nutrient distribution in British Columbia Interior soils.

Nutrients in kg ha–1 (% of total)Soil layer Nitrogen Phosphorus Potassium

Forest floor 14�0 (44%) 112 (�2%) 224 (7�%)0-20 cm 10�0 1� ��20-40 cm �20 � 2�Total ��20 1�� 0�

Forest Floor Displacement Hazard

Forestfloordisplacementisthemechanicalmovementoftheupperorganicmaterialsbyequipmentandmovementoflogs.Itinvolvesexcavation,scalping,mineralsoilexposure,andburialof theforest floor.Theeffectsof forest floordisplacement range from beneficial to detrimental, depending on site factors(e.g.mineralsoilcharacteristics)andhowfartheforestfloorisdisplacedfromtheseedlings.

Forestfloorstypicallyrepresentamajorcomponentofthenutrientcapitalonaforestsite.IntheBritishColumbiaInterior,itisnotuncommonfortheforestfloortocontainover50%ofthesoilnitrogenand80%ofthephosphorus(table1).GiventhatmanyInteriorsitesareconsiderednitrogendeficient,conservationoftheforestfloorisimportant.Ondeeperash-caporolder,richersoils,muchofthenutrientcapitaloccursinthemineraltopsoilandforestfloordisplacementmaybeoflessconcern.

Twoaspectsofforestfloordisplacementcanproducesoildegradation:

• Redistributionandlossofnutrients(e.g.chemicallyboundandunavailableinthemineralsoil,andaccelerateddecompositionoforganicmatter).

• Exposureofunfavourablerootingmedium.

AreviewofforestfloordisplacementandimplicationsfortreegrowthintheSouthernBritishColumbiaInteriorfoundthatwhiletherewereafewtrendsinsoilnutrientlevels,itwasdifficulttorelatedisplacementtoanynegativeeffectsontreegrowth(Hickling1997). IncooperationwithPopeandTalbotLtd.,weinstalledlong-termmonitoringplotsonvariousdisturbancetypesincludingsomeassociatedwithstumping(Hickling1998).

Most forestoperationswerewellbelow the forest floordisplacement limitsoriginallysetintheFPC,sodeterminingtheforestfloordisplacementhazardisnolongerofficiallyrequiredforharvestplanningandpermitting.However,useofthishazardinterpretationissupportedandrecommendedforplanningdispersedskiddingonsteeperslopes,rehabilitationofsoildisturbance,androotrottreat-ments.ForestfloordisplacementisalsomoreofaconcernoncalcareoussoilsduetothehigherpHofthemineralsoil

Surface Soil Erosion Hazard

Surfacesoilerosionisthewearingawayoftheearth’ssurfacebywaterandincludessplash,rill,andgullyerosion.Ithason-siteimpacts(soilloss,nutrientloss,lowerproductivity)andoff-siteimpacts(waterquality,sedimentation,habitatimpacts).Thesurfacesoilerosionhazardkeyfocusesonon-siteerosionandcon-servationofthefertiletopsoillayersneardevelopingseedlings.ThescienceandrationalefortheBritishColumbiakeywerelaidoutinCarrandothers(1991),andtheratingweightingstestedintheNelsonForestRegionbyCommandeur(1994),resulting inmodifications to the finalkeycurrently inuse.Otherassessmentsmaybeusedforhaulroaderosionandsedimentdeliverytostreams.Haulroadsandlandingsareofconcernbecauseerosionanddrainagediversionscanleadtosedimentationandstabilityproblems.Theyrequirecarefullayoutandattentiontoerosionhazardonhaulroadsandminimizingerosionandsedimentationduringconstructionandmaintenance.

Defining Soil Disturbance

Atechnicaldefinitionofsoildisturbanceisanydisturbancethatchangesthephysical,chemical,orbiologicalpropertiesofthesoil(Lewisandothers1991).Itisnotalwaysnegative.Foresterscommonlyprescribepurposefulsoildisturbanceas site preparation for seedling planting and establishment; these disturbancetypesareoftennotcountedinstandards(e.g.,underFRPAinBritishColumbia).Bycontrollinghowweharvestasite,wecancreatemore“sitepreparation”typedisturbanceandkeepmostofthepotentiallydetrimentaldisturbanceconfinedtotravelcorridors;thesemaintrailsmaythenberehabilitatedafterharvesting,asappropriate.Wheneverplanningsoildisturbance,thepreservationandrestorationofnaturaldrainagepatternsshouldbetheprimarygoal(necessaryrepetition).

Thestrategiesdescribedinthisdocumentstrikeabalancebetween“favourable”and“detrimental”disturbancebylimitingtheamountof“counted”soildisturbance.Regionally applicable soil disturbance standards recognize that some level ofdisturbanceisnecessarytopermitaccesstotimber.Counteddisturbanceusually

includesmaintrailsandruts/impressionsofcertaindimensions,andundersomeschemes(e.g.,FRPAinBritishColumbia)alsoincludewideordeepgougesintothesoil.Thosedevelopingandimplementingaharvestingstrategyneedtorecognizethatonmoresensitivesites,disturbancetypesthat“count”maybecreatedmoreeasilyandmaybecountedsooner(e.g.,inInteriorBritishColumbia5-cmrutsandimpressionsonHighandVeryHighCompactionhazard,asopposedto15cmonothersoils;whenErosion,Displacement,orCompactionhazardsareVeryHigh).Onsiteswithlowerhazardratings,lessdisturbancecategoriesmaybecounted.

Theactualeffectofagivensoildisturbanceontreegrowthwilldependonthemostgrowth-limitingfactorsonagivensiteandhowthesefactorschangeoverthecourseofarotation.IntheBritishColumbiaInterior,commongrowth-limit-ingfactorsinclude:competingvegetation,soilmoisture(droughtorexcess),soiltemperature,summerfrost,rootingsubstrate(volume),soilnutritionalproblems(e.g.,calcareoussoils),androotrot.Theneteffectongrowthwillalsodependonwhethersoildisturbancehasintroducedanewlimitation,suchasreducedsoilaerationfromcompaction.Long-termeffectscouldincludeincreasedsusceptibilitytoblowdownbecauseofpoorrootingindetrimentallydisturbedsoil.

Regional ecology guides often summarize common growth-limiting factorsfor various ecosystems (Braumandl andCurran1992), andamodelhasbeendeveloped for comparingdisturbanceeffectsongrowth-limiting factorswhendecidingonsitepreparationprescriptions(CurranandJohnston1992;Sachsandothers2004).

Regardlessoftheactualtreegrowtheffects,anumberofsoildisturbancetypesarealsoofconcernbecauseofpotentialeffectsonsiteandslopehydrologyandthepotentialfordownslopeimpacts.On-sitehydrologychangesaredifficulttostudybutweneedtoerrontheconservativesideconsideringthatmuchofBritishColumbiaisnotflatandsummerdroughtisoftenoneofthemostgrowth-limit-ing factorsonmanysites (effectsonhydrologymayconfoundtreegrowthonapparently“undisturbed”micrositesintreegrowthstudies).Similarhydrologicconcernshavebeenvoicedbyotherresearchersinthelocalarea(Kuennenandothers1979).

Synthesis of Above Knowledge and Principles in Our Forest Practices _____________________________________________

Machine-Based Practices

Forestharvest,sitepreparation,andfuelmanagementtreatmentsaremostcom-monlyaccomplishedthroughtheuseofmachinery.Inthecaseoftimberharvestorfuels,thismayoccurthroughaerial,cable,orground-basedequipment.Becauseground-basedharvestingtypicallycreatesthemostdisturbance,it isdiscussedbelowbuttheprinciplesremainthesamefortheothermethods.

Basedontheenvironmentalframeworkdescribedintheprecedingsection,agivenharvestingstrategyshouldmeetthefollowingfourrequirements:

1. Besitespecificandresponsivetothesoilsensitivitiesonsiteanddownslope. 2. Offerareasonableamountofindependencefromclimaticinterruptions,. 3. Incorporaterehabilitation,ifnecessary,tolowerdisturbancebelowguidelines. 4. Itmustinstillenoughconfidenceatalllevelsofapprovalandoperations.

Inthe1990sweworkedonanumberoftrialswithIndustryandDistrictstaff,toaddressconcernsaboutmanagingharvestingsoildisturbance.Trialshavead-dressedtreegrowthonrehabilitatedskidroads(DykstraandCurran1999),haulroads(Curran,unpublisheddata),andlandings(BulmerandCurran1999a).Memoswerecirculatedandaspecialpublication(Curran1999)summarizedsimplefieldtestsdevelopedduringoperationaltrialsofseasonalharvestingconstraints(i.e.,“howwetistoowet?”and“howmuchfrostisenoughfrost?”).Otherresearchtrialshavebeensuccessfulindemonstratingthefeasibilityofrehabilitatingsoildisturbance(BulmerandCurran1999b).Combined,thesetrialsweredesignedtotesttreegrowthonrehabilitateddisturbanceanddevelopstrategiestoreducethedependencyonweatherconditionsandreduceshutdownofoperationsduringwetterconditions.Researchandpracticalinnovationarestillongoing,andfurtherfieldguideswillbeproducedaswarranted(e.g.,wearedevelopingasimplersoiltexturekeyatthistime).

Basedonindustryinnovation,practicalexperience,andresearchtrials,wehaveidentifiedfourkeystrategiesthatwefeelmeettheabovecriteria:

a) closetrailspacingwithrehabilitation, b) closelyspacedtemporaryspur(haul)roadswithrehabilitation, c) combinationdesignatedanddispersed(random)skidding,and d) hoe-chucking,Interiorstyle(i.e.,forwardingtowiderspacedtrails).

Thesestrategiesmayormaynotincludefullymechanizedharvesting,eitherwithcut-to-lengthfeller-processorsandforwarders,orwithfeller-bunchersandgrappleskidders.Thestrategiesalsomayoffertheopportunitytoreducesitepreparationcostsbycreatingdisturbanceduringtheharvestingorrehabilitationphases.EachstrategyisdescribedinmoredetailinCurran(1999).OtherharvestingstrategieshavebeendescribedformeetingsoildisturbancestandardsundersiteconditionsinwesternWashingtonandOregonbyHeningerandothers(1997).Again,theobjective is tomatch equipment capabilities to site sensitivity to disturbance.Ground-basedequipmentmaybe restricted todesignated trailsorallowed totraveloverlanddependingonthesoilandclimaticconditions.

Studies on ash-cap influenced and similar soils in southern Interior BritishColumbiahaveshownthatlargeamountsofsoildisturbancecanoccurduringmechanicalrootremovalforrootdiseasemanagement(QuesnelandCurran2000;Curran, unpublished data). Tree growth responses to these disturbances varywithsitegrowthlimitingfactorsandovertime.OntwositesonsimilarclimateinsouthernBritishColumbia,stumpremovaltreatmentshaddifferingeffects(fig.4).Onanash-capinfluencedsoilatPhoenix,soildisturbanceeitherincreasedordidnotnegativelyaffecttreegrowth;whereasonasoilontheGatesCreeksitethathadmoreclay(12%versus4%),therewasaclearnegativetrendwithtreegrowthanddisturbanceseverity.Thelong-termgrowthtrendattheGatesCreeksiteisinterestingasitclearlydemonstratestheneedforlong-termtreegrowthresponsedata(fig.5).

Insect and DiseaseSome forest insects and pathogens are opportunistic organisms that cause

primarydamagetostressedhosttrees.Stressmayoccurduetosoildisturbanceeffectsontreegrowingenvironment,climatechangeresultingintemperatureormoisturestress,otherbioticorabioticenvironmentalfactors,ormultipleinteract-ingfactors.Interactingfactorsthatcontributetopestoutbreakarecomplex.For

Figure 4—Fifteen-year volume of Douglas-fir seedlings growing in different disturbance types on the Canadian Forest Service Gates Creek and Phoenix stumping trial sites in southern British Columbia, which are gravelly sandy loam textured with 12% clay at Gates Creek and 4% clay at Phoenix (Curran and others 200�a adapted from Wass and Senyk 1999).

Figure 5—Comparison of relative growth of Douglas-fir on a stump removal trial in southern British Columbia at �, 10 and 1� years since treatment. All data is relative to the undisturbed condition (Curran and others 200�a adapted from Wass and Senyk 1999).

example,largeareasofbarkbeetleinfestationsaresometimesattributedtoclimatechangeand/orrootdisease interactions (PartridgeandMiller1972).However,insectattackisalsodependentuponinherentdynamicsofinsectbehavior.ThefollowingtextfocusesonrootdiseaseorganismsinInlandNorthwest.

Environmental Factors Affecting the Distribution and Activity of Root Diseases

Biophysical Setting—Armillaria rootdisease (primarilycausedbyArmillaria ostoyae)andAnnosus rootdisease (causedbyHeterobasidion annonsum)arewidelydistributedinwesternconiferforests.Off-siteplantings,woundedtrees,andtreesgrowingoncompactedsoilsor inareaswithdrainageproblemsareparticularlylikelytobeaffectedbyArmillariarootdisease(GoheenandOtrosina1998;Wiensczykandothers1997).Douglas-firdominatedstands innorthernandcentralIdahoandnortheasternWashingtonexperiencesubstantialmortalityfromAnnosusrootdisease,especiallyondrysites (Schmittandothers2000).However,insoutherninteriorBC,Morrisonandothers(2000),foundsignificantlyhigherratesofArmillariasp.infectionondrysitesthanmoistorwetsites;andonceinfected,treesondriersiteswerelessabletoresistinfectionandweremorelikelytoshowabovegroundsymptoms.

Laminated root rot, (causedbyPhellinus weirii),occursmainly inhemlock,westernredcedarandgrandfirhabitattypesontheLoloNationalForest,butinfrequentlyinDouglas-firandsubalpinefirhabitattypes,whileArmillariaandAnnosumrootdiseasearedistributedmorewidely(Bylerandothers,1990).Hagleandothers(1994)similarlyfoundrootdiseasemostsevereingrandfirhabitattypes,andlowseveritydiseaseratingsoccurredmostoftenonDouglas-firhabitattypes.Declinesindiseaseseveritywerenotedafter160yearsasthemoresusceptiblespeciesdiedoutofthestand.TheysuggestthatgrandfirhabitattypesaremostlikelytosupportgrandfirandDouglas-firasseralandclimaxspecies,andthesearethemostsusceptiblespecies.

OntheLoloNationalForest,Bylerandothers(1990),foundhigherprobabili-tiesofArmillariarootdiseaseonDouglas-firhabitattypesonsoutherlyaspects.Moderateslopeshadahigherincidencethaneitherflatorverysteepslopes.

Soil Physical Properties—Inanotherstudy,Armillariaspp.infectionlevelsde-creasedwithincreasingclaycontent,whichiscorrelatedwithmoisture-holdingability (Wiensczykandothers,1997).This isconsistentwiththehazardratingsystemofFroelichandothers(1977).IntheWiensczykstudy,sandysoilsweremorehighlycorrelatedwithArmillaria spp.activity inblackspruce thanweresiltysoils,andasmoistureregimeincreased(basedonmottlesandgleying),Ar-millariaspp.frequencydecreased.ThismaybeduetoreducedgrowthofArmil-lariarhizomorphsinfinertexturedandmoistersoils,ortoimprovedtreevigor.Sand,largesoilpores,andhighbulkdensitywerealsopositivelycorrelatedwithAnnosumrootdiseaseinloblollypineplantations(Alexanderandothers,1975).It is thought that rapid infiltration in sandysoilsallowedeasy translocationofrootrotspores.Bakerandothers(1993)alsofoundthatlowsiltintheAhorizonwasanimportantpredictorofH. annosum infection.Blenisandothers(1989)alsofoundclayloamtobeleastfavorableforArmillariarootdiseaseandsandyloamthemostfavorable.Thepathogenisknowntobesensitivetolowlevelsofoxygenandhighlevelsofcarbondioxide.

Soil Chemical Properties—Armillaria ostoyaeinfectionlevelswerefoundtoincreasewithincreasingphosphorousintheAhorizon(Wiensczykandothers1997).However,phosphorousinash-capsurfacesoilsisoftenheldinunavailableformandmaynotlocallycontributetoinfection.Reducedphosphorousmaylimittreerootelongation,whichcouldreducethelikelihoodofundergroundcontactwithA. ostoyae.

Rishbeth(1951)foundH. annosuminfectionratesfromstumpstobelowerinacidthanalkalinesoils.Heattributesthistocompetingfungiinmoreacidsoils.Bakerandothers(1993)foundH. annosum infectionincidencetobelowerinacidsoils,asdidBlenisandothers(1989).

Soil Microbiology—Rootmicroflora,suchasActinomycetesandfungi(e.g.,Trichodermaspp.,Phlebiopsisspp.,Bjerkanderaspp.,Hypholomasp.,etc.),canhavefungistaticeffectsonrootpathogens(HagleandShaw1991;HoldenreiderandGreig1998;Nelson1964,1973;NelsonandThies1985,1986;Raziq2000).Ithasbeensuggestedthatmixedstandswithfewerpotentialhostspecies,andinterruptionofsuccessionwithshrubandothernon-susceptiblespeciesreduceH. annosum inoculum(JohanssonandMarklund,1980)bysupportingenhancedpopulationsofActinomycetes.ChapmanandXiao(2000)confirmedtheabilityofasaprophyticfungus,Hypholoma fasciculare,toout-competeA. ostoyaeonavarietyofnonlivingsubstrates,suchasstumps.VeechandBoyce(1964)alsofoundhigher levelsofsoil fungi,Actinomycetes,andbacteria thaninareasofhigherH. annosuminfection.Greig(1962)alsofounddevelopmentofAnnosum rootdiseasetobelowerinplantationsestablishedonareasformerlyoccupiedbyhardwoodsthanonsecond-rotationconiferplantations.This“diversityofsoilmicroflora” ishypothesized tobemore typicalofnaturaldisturbance regimesthanstandsaffectedbyfiresuppressionandemphasisononeortwosusceptiblecropspecies,likegrandfirandDouglas-fir.

Ectomycorrhizalfungiassociatedwithtreerootsareknowntobeimportantformoistureandnutrientrelationshipsofthehosttree(Harveyandothers1986,1987).Decayedsoilwoodpromotesthisassociation.Rootpathogensmayinteractdirectlywithmycorrhizaesothatbiomassandenergyreservesofallpartiesarereduced(Graham2001;Sharmaandothers1992),butsometimespathogeneffectsonthehosttreearereduced(Morinandothers1999).Thiscomplexinteractionsuggestsweneed tosustainacontinuoussupplyof theorganicmaterials thatsupporthealthymycorrhizalpopulations.

Relation to Properties of Volcanic Ash—Surface soils formed in volcanicashtendtobesiltyintexture,havehighporosity,andlowbulkdensity,andlowinherentnutrientstatus,andlownutrient-holdingcapacity(McDanielandothers2005).Theymayadsorbphosphorusandholditinanunavailableform.Acid-ityistypicallyslightlyacidtoneutral.Treerootsareoftenconcentratedinthevolcanicashlayer,suggestingthatrootcontactcouldbecommonanddistancefromstumpinoculationpoint to live rootwouldbeshort.Thiswouldmake iteasier for infections to spread. High moisture-holding capacity suggests thatdrought-inducedstressduringsummerswouldbesomewhatmitigated,butthatthiscapacitywouldbereducedbycompactionordisplacement.Volcanicashishighlycorrelatedwithgrandfir,cedar,hemlock,andsubalpinefirhabitatseries,andtoalesserextentwithDouglas-fir.

Management Effects—Fireexclusion,harvestoflesssusceptiblepineandlarch,anddeclinesinwhitepineduetoexoticblisterrust(Cronartium ribicola)haveallcontributedtotheincreaseinmoresusceptibleDouglas-firandgrandfir,andmoistureandnutrientstress,increasingtheprevalenceofrootdiseaseintherangeofvolcanicashsoils.Morestudesareneededtodeterminetheeffectsofpartialharvestandsoilcompaction/displacementonrootdiseaseinmanagedstands.

Climate Change, Root Disease, and Management on Volcanic Ash-cap Soils

Climatechangecanresultinmaturetreesthataremaladaptedtotheirenvi-ronment,whichcanincreasevulnerabilitytopathogens(AyresandLombardero,2000),aswellasotherdisturbanceslikefireorinsects.IntheInteriorNorthwest,increasing temperatures and reduced summer moisture (McKenzie and others2004;Moteandothers2003)increasestressontreesinmarginalsites(thinash-cap,compactedsoils),whichmaymakethemmoresusceptibletorootdiseases.Physiologicalmodelstopredicthowtreedefenseswouldalterwithclimatechangearelacking.Effectsofclimatechangeonrootdiseaseandcompetingorganismsarenotknown.

Firesuppressionandsubsequentlymoreseverefiresmayincreasetherateofrootdiseasebyprovidingmorefire-scarredtreewoundsasentrancepoints(OtrosinaandGarbelotto1997).Fireexclusionleadingtodominanceofsusceptibletruefirsandhighlevelsofrootdiseasewouldalsoleadtoincreasedsusceptibilitytofireandlargeinsectoutbreaks.Higherdensitystandsduetofireexclusioncouldincreasethelikelihoodofbelowgroundspreadofthepathogenfromtreetotree.Longerperiodsofhighheatanddroughtcouldsuppresssporegerminationandstumpcolonizationforlongerperiodsinthesummer,althoughBendz-HellgrenandStenlid(1998)foundnoeffectoftemperatureonstumpcolonizationbyH. annosum.

Management Opportunities:

• Limitmanagementinducedstressbyconfiningsoilcompactionanddisplace-menttolimitedareasandrehabilitatingthemafteruse.

• Provideconnectionsforspeciestomoveinresponsetochangedclimaticcontext(maintainingcontinuityofspeciesinspace,whileallowingformovement).

• Usespeciesanddensitymanagementtoallowforestspeciestousedistur-banceassteppingstonesformigration.

• Introduceandsustainspeciesresistanttorootdisease. • RootremovalhasbeenproposedtocontrolArmillariarootdisease(Roth

andothers2000),butsomestudieshaveconcludedthatinoculumremovalcannotbecompleteenoughtochangethedynamicsofrootdiseasedevelop-ment(Reavesandothers1993).Theassociatedsoildisturbance,particularlyinash-capsoils,islikelytohavedeleteriousphysicaleffects.

Theissueofsoilrestorationtorecoversuitablemoistureandairrelationshipsis complicated by other factors. Soil disturbance associated with roads, skidtrails,andprecommercial thinning (Hessburgandothers2001)wascorrelatedwithincidenceofblackstainrootdisease(causedbyLeptographium wageneri)insouthwestOregon.Alternatively,subsoilingtoalleviatesoilcompactionmayresultinrootdamageanddiebackofanyresidualtrees,attractingrootfeedingbeetles that carry black stain root disease. Kliejunas and Otrosina (1997) and

Otrosinaandothers(1996)foundhigherlevelsofergosterolinsubsoiledareas,whichindicatedhigherlevelsoffungaldecomposeractivity.Thiswasattributedtosoildisplacementandrootsevering.Thissuggestsmanagersshouldlimittheextentofcompactedareasasmuchaspossibleandavoidsubsoilingneartreestoavoidbothaboveandbelowgrounddamage.Stumpremovalcouldhavesimilareffectsinadjacentlivetrees.

Analysis of North Idaho Root Disease Trends in Relation to Soil and Site Factors

SueHagle (Pathologist,USDAForestService,Region1) ratedstandswithinrandomlyselectedsubcompartmentsforrootdiseaseactivityusingphotointerpre-tationonascaleof0to9(Hagleandothers2000).OnthethreeIdahoNationalForests(IdahoPanhandle,Clearwater,andNezPerce)analyzedhere,1,204plotswereavailable,but11ofthesedidnothavegeologicinformationand29didnothavesoilsurveyinformation.Thestandpolygonswereinteractedwithgeospa-tiallayersincludingsoilsurveymapunits,lithology,meanannualprecipitation,elevation,aspect,latitude,longitude,andslope.

Soilsurveymapunitswereclassifiedintofourclassesbasedonvolcanicashdepth:

1:Nodescribedvolcanicashinfluence 2:Thinormixedash 3:Andicsubgroups 4:Thickash(Andosols)

Wheresoil typevariedbyaspect,aspectwasused to refine theashdepthfactor.

Geologicgroupsweredevelopedbasedonliteraturedescribingassociationsbetweenrootdiseaseandrocktype(GarrisonandMoore1998;Mooreandothers2004).Thisprocesswascomplicatedbydifferentscales,notation,anddepthofdescriptionofavailablegeologicmaps.Wetriedtoidentifypotentialstrongas-sociationsbyspatialexplorationofrootdiseaseactivityandgeologicformation.Patternsthatappearedstronginoneareawerenotconsistentinotherareas.Theresultinggroupsusedare:

2 =Granitics,predominantlyCretaceous,butalsoJurassic(292samples). 3 =Recentmetamorphics(youngerthanBeltAge)(21samples). 4 =Beltagemetamorphics,butnotincludingBeltquartzitesdescribedunder

11.(666samples).Thesewereexpectedtohavehigherinherentfertility. 5 =Tertiaryandmorerecentsediments(3samples). 6 =SevenDevilsvolcanicsofTriassicandPermianage(20samples).Thesesites

wereomittedfromthisanalysisbecausetheyarethoughttobeanomalous.Theyhadveryhighrootdiseaseactivityratings.Trendsandsignificanceweresimilarwithandwithoutthesesamples.

7 =Undifferentiated,suchasglacialdepositsoralluvium(65samples). 8 =Othervolcanics(2samples). 9 =Limestonenosamples. 10 =Beltagesedimentsnosamples. 11 =Beltquartzites(MiddleWallacequartzites,StripedPeakformation,Revett

quartzite,andPrichardquartzite(94samples).Thesewereexpectedtohavethelowestinherentfertility.

EachstandwasadditionallyassignedtoamoistureandtemperaturegradientclassafterMcDonaldandothers(2000)usingthehabitattypeinformationas-sociatedwitheachstandpolygon:

Understory: Moisture RegimeNodata 0Drygrass 1Dryshrub 2Dryherb 3Moistherb 4Wetherb 5Wetfern 6Wetshrub 7

Overstory: Temperature RegimeNodata 0Coldfir 1Coolfir 2Cedarhemlock 3Douglas-fir 4Ponderosapine 5Pinyonjuniper 6

Thefollowingtablesandplotsdisplayexploratoryanalysisoftheassociationofrootdiseaseactivity(usingan8classrankingsystem)andcategoricalenvironmen-talvariables.Shownarethemedian,interquartilerange,extremes,andpossibleoutliers.Nopatternisapparentforaspectclassandrootdiseaseranking,

Root Disease and Ash Depth

Thinormixedashisassociatedwithhigherincidenceofrootdisease(table2).Lowrootdiseaseactivityassociatedwithareasofnovolcanicashareusuallyinverydrysteepslopesorpoorlydrainedareaswheresoilsareformedinmixedalluvium.

Soilswithnoashinfluencehavesignificantlylowerrootdiseaseactivity,butAndicsoilsandAndosolsdonotdiffersignificantly.

Table 2—Ash-cap depth as related to root disease ranking.

Ash Depth N

Mean RootDiseaseRanking* 95% C.I.

1 – None 25 2.2 1.5-2.9

2 – Thin or mixed 198 3.6 3.3-3.9

3 – Andic 247 3.2 2.9-3.4

4 – Andosol 638 3.0 2.9-3.2*See Hagle and others (2000) for detailed root disease activity scale.

Geologic Group

No strong trends were noted, however there were some differences among lithologic groups.

Recentmetamorphicsshowedgreaterrootdiseaseactivitythaninundifferenti-ateddeposits(table3).Thegreatvariabilityinrecentsediments(group5)suggestsaneedforfurtherrefinementofthisclass.Beltagemetamorphics(group4)showedrelativelylowrootdiseaseactivity,withnumeroussamples,andweresignificantlyless thangranitics, recentmetamorphics,andBeltquartzites.Undifferentiatedrocktypes(recentdeposits)alsoshowedlowrootdiseaseactivity.TheBeltAgequartzites,anticipatedtobenaturallylowinpotassiumandwithhighlevelsofrootdiseaseactivity,weresignificantlyhigherthanotherBeltmetamorphicsandundifferentiatedrocktypes,butdidnotdifferfromgranitics,recentsediments,orrecentmetamorphics.

Table 3—Influence of geologic group on disease incidence.

Geologic Group N

2 – Granitics 292 3.5 3.3-3.7

3 – Metamorphics(not Belt Age)

21 3.9 2.8-4.9

4 – Belt AgeMetamorphics/notquartzites

666 2.9 2.8-3.0

5 – Tertiary andmore recentsediments

3 4.3 .5-8.1

7 – Undifferentiated(recent glacialdeposits or alluvium)

65 2.9 2.5-3.3

8 – Other volcanics 2 3.5 NA

11 – Belt quartzites 94 3.5 3.1-3.9

*See Hagle and others (2000) for detailed root disease activity scale.

Root Disease and Forest

TheIdahoPanhandleNationalForesthadthelowestdiseaseranking,followedbytheClearwaterNationalForest,andthenNezPerceNationalForest(table4).Thesedifferencescouldbecausedbydriersoils,changesingeology,soilnutri-tion,orotherinherentsitephysical,chemical,orbiologicalproperties.

Table 4—National Forest and incidence of disease.

National Forest N

4 – Idaho Panhandle 639 2.7 2.6-2.9

5 – Clearwater 331 3.4 3.2-3.6

17 – Nez Perce 173 4.0 3.7-4.3

Root Disease and Potential Vegetation (Habitat Type Group)

PotentialVegetationisanindicatorofsoilmoistureandtemperatureregimesandconstrainswhethersusceptiblespeciesarelikelytooccurasseralorclimaxonthesite.Whenhabitattypes(Cooperandothers1991)aregroupedaccord-ingtoJones(2004),itisevidentthatthosehabitattypesmostlikelytosupportsusceptiblegrandfirorDouglas-firandshowhigherlevelsofrootdiseaseactivity(datanotshown).Theoccurrenceandseverityofrootdiseasedependsstronglyontheabundanceofasusceptiblehost.Siteswithalongerhistoryofdominancebysuitablehostspecieswilllikelyhaveaccruedhigherlevelsoffungalbiomass.DriergrandfirandDouglas-firhabitattypes,whicharemorelikelytosupportmoreponderosapine,showlowerlevelsofrootdiseaseactivity.Itisinterestingtonotethatsomeextremelyhighvaluesofrootdiseaseactivityareassociatedwithmoremoistcedarorwesternhemlockhabitattypegroups.Itispossiblethatthesesitesarecapableofveryhighlevelsofinoculumwhereseralwhitepinehasbeeneliminatedforlongperiods.

Moisture and Temperature Regime

UsingthemoistureandtemperatureindicesdefinedbyMcDonaldandoth-ers(2000),wecompareddiseaserankingagainstmoistureindicator(understoryassociation)andtemperatureindicator(overstoryseries).

Siteswithmoderatelydrymoistureregimes(dryshrub)hadthehighestrootdiseaseactivity,anddifferedfromdrygrassanddryshrub,butnotmoistherb(table5).ThismaybeduetothehighincidenceofsusceptibleDouglas-fironthesemoisturesettings.

Siteswithmoderatelywarmtemperatureregimes(Douglas-fir)hadthehighestrootdiseaseactivity,anddifferedsignificantlyfromcoldfirandponderosapine.Coolfirtemperatureregimeshadhigherrootdiseasethancoldfir,cedarhemlock,andponderosapine(table6).Again,thepresenceofsusceptiblehostspeciesishighlycorrelatedwiththesetemperatureregimes.

Table 5—Root disease ranking as related to understory moisture indicator.

Moisture Regime N

1 – Dry grass 12 2.2 1.1-3.2

2 – Dry shrub 89 3.4 2.9-3.8

3 – Dry herb 303 2.9 2.7-3.1

4 – Moist herb 734 3.2 3.1-3.3

5 – Wet herb 1 3 NA

6 – Wet fern 1 0 NA

7 – Wet shrub 1 1 NA

Table 6—Root disease ranking as related to temperature regime.

Temperature Regime N

1 – Cold fir 366 3.0 2.8-3.2

2 – Cool fir 153 3.6 3.3-3.9

3 – Cedar hemlock 528 3.1 2.9-3.2

4 – Douglas-fir 90 3.5 3.0-3.9

5 – Ponderosa pine 3 1.3 0-4.2

Association of Root Disease Ranking with Numeric Variables

Themostecologicallysignificantcorrelationsappeartobethatrootdiseaseactivity is positively associated with steep slopes, southerly latitude, westerlylongitude,potential forhost species (basedonhabitat typecover tables),anddecreasingannualprecipitation.

Conclusions _____________________________________________________Ash-capsoilsaresusceptibletodisturbance;schemestopredictcompaction,

displacement,anderosionhazardsareusefulinforestmanagementapplication.Whether more or less disturbance should be permitted on ash-cap soils is acontroversialtopicanditislikelymoreimportanttofocusontheindividualsitehazardsbecauseash-capsoilscanvaryconsiderablyintheirstateofweather-ing,texture,depthandinter-mixingwithothersoilmaterials.MachinetrafficcanbemanagedandasdemonstratedinBulmerandothers(thisproceedings),andmitigatedthroughrehabilitationinasetofharvest(machine-traffic)strategiesthatconsidersite.

Regardingrootdiseaseonash-capsoils,thispreliminarycoarse-scaleinves-tigation suggests some potential relationships among root disease (primarilyArmillaria in Idaho)and soil and site factors.The strong relationshipbetweenpresence of susceptible host and development of fungal biomass may be thestrongestcausalagent,andthesoilandsitefactorspromotethepresenceofthesusceptiblehost.

Thickerashsoilsofmorenortherlyareasarerelatedtohabitattypesthathis-toricallysupportedwhitepineandahigherdiversityoflesssusceptiblespecies.Thesemoremesicenvironmentsalsofillinwithotherspeciesrapidlyafterrootdiseasemortalityoccurs,sohigherlevelsofrootdiseaseactivityaremoredifficulttodiscern(Hagle,personalcommunication,2006).

Recommendations ______________________________________________Sustainablesoilmanagementonash-capsoilsneedstofollowprotocolsdeveloped

forallsiteswherebyanadaptivemanagement/continuousimprovementprocessneedstobesupportedbyresearch,bestmanagementpractices,andstrategiesthatincludealltypesofmonitoring(compliance,effectivenessandvalidation).

Developmentofacommonapproachtodescribingsoildisturbanceandsoildisturbancehazardswillgoalongwaytowardmoreeffectivesharingofmanage-mentexperiencesonash-capsoils.

Moreworkisneededonthelong-termeffectsofcumulativeaerialextentofsoildisturbanceandonsoildisturbancecategories torefine theseandhazardratingsystems.

For the root disease work, more site-specific evaluation of soil properties,standhistory,andgeologicparentmaterials,bothmineralogicalcompositionandweatheringstate,wouldhelptosortouttheserelationships.

Acknowledgments ______________________________________________TheauthorsthankDr.R.E.Miller,emeritusresearchscientistatUSDAForest

Service,PacificNorthwestResearchStationforhisreviewofthemanuscript,andSueHagle,pathologistforUSDAForestServiceRegion1forherhelpfuladviceandreviewoftherootdiseasepartofthispaper.

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