简介：Background:FrequentoutbreaksofinsectsanddiseaseshavebeenrecordedinthenativeforestsofwesternNorthAmericaduringthelastfewdecades,butthedistributionoftheseoutbreakshasbeenfarfromuniform.Insomecases,recentclimaticvariationsmayexplainsomeofthisspatialvariationalongwiththepresenceofexpansiveforestscomposedofdense,oldertrees.Forestmanagersandpolicymakerswouldbenefitifareasespeciallypronetodisturbancecouldberecognizedsothatmitigatingactionscouldbetaken.Methods:Weusetwoponderosapine-dominatedsitesinwesternMontana,U.S.A.toapplyamodelingapproachthatcouplesinformationacquiredviaremotesensing,soilsurveys,andlocalweatherstationstoassesswherebarkbeetleoutbreaksmightfirstoccurandwhy.Althoughtherewasageneraldownwardtrendinprecipitationforbothsitesovertheperiodbetween1998and2010(slope=-1.3,R2=0.08),interannualvariabilitywashigh.Someyearsshowedlargeincreasesfollowedbysharpdecreases.Bothsiteshadsimilartopographyandfirehistories,butbarkbeetleactivityoccurredearlier(circa2000to2001)andmoreseverelyononesitethanontheother.Theinitialcanopydensityofthetwositeswasalsosimilar,withleafareaindicesrangingbetween1.7-2.0m2?m-2.WewonderedifthedifferenceinbarkbeetleactivitywasrelatedtosoilsthatwerehigherinclaycontentatsiteIthanatsiteII.Toassessthispossibility,weappliedaprocess-basedstandgrowthmodel(3-PG)toanalyzethedataandevaluatethehypotheses.Results:Wefoundthatwhenwetyearswerefollowedbydrieryears,thesimulatedannualwoodproductionperunitofleafarea,ameasureoftreevigor,droppedbelowacriticalthresholdonsiteIbutnotonsiteII.Conclusion:Weconcludedthatthedifferenceinvulnerabilityofthetwostandstobeetleoutbreakscanbeexplainedlargelybydifferencesingrossphotosynthesisattributedtothefactthatanequivalentamountofstoredwaterintherootingzone(100m

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简介：Elevatedatmosphericnitrogen(N)depositionhasbeendetectedinmanyregionsofChina,butitseffectsonsoilNtransformationintemperateforestecosystemsarenotwellknown.WethereforesimulatedNdepositionwithfourlevelsofNadditionrate(N0,N30,N60,andN120)for6yearsinanold-growthtemperateforestinXiaoxing’anMountainsinNortheasternChina.WemeasuredgrossNtransformationratesinthelaboratoryusing15NtracingtechnologytoexploretheeffectsofNdepositiononsoilgrossNtransformationstakingadvantageofNdepositionsoils.NosignificantdifferencesingrosssoilNtransformationrateswereobservedafter6yearsofNdepositionwithvariouslevelsofNadditionrate.ForallNdepositionsoils,thegrossNH4+immobilizationrateswereconsistentlylowerthanthegrossNmineralizationrates,leadingtonetNmineralization.Nitrate(NO3-)wasprimarilyproducedviaoxidationofNH4+(i.e.,autotrophicnitrification),whereasoxidationoforganicN(i.e.,heterotrophicnitrification)wasnegligible.Differencesbetweenthequantityofammonia-oxidizingbacteriaandammonia-oxidizingarchaeawerenotsignificantforanytreatment,whichlikelyexplainsthelackofasignificanteffectongrossnitrificationrates.GrossnitrificationratesweremuchhigherthanthetotalNO3-consumptionrates,resultinginabuild-upofNO3-,whichhighlightsthehighriskofNlossesviaNO3-leachingorgaseousNemissionsfromsoils.ThisresponseisoppositethatoftypicalN-limitedtemperateforestssufferingfromNdeposition,suggestingthattheinvestigatedold-growthtemperateforestecosystemislikelytoapproachNsaturation.

简介：Background:Forestmanagementstrategiessuchasthinninghavelongbeenusedtoenhanceecosystemfunctions,especiallyinplantations.Thinninginplantationswithhighdeerdensity,however,maynotyieldadesiredincreaseinunderstoryvegetationbecausedeergrazeongerminatingplantsafterthinning.Here,weexaminethechangesinunderstoryvegetationafterthinninginplantationsthathavebeenovergrazedbysikadeertoprovideinsightintotheeffectsofthinningonecosystemfunctionssuchassoilconservationandbiologicaldiversity.Methods:WeconductedoursurveyintheTanzawaMountainsofeasternJapan.Wesurveyedthechangeinunderstoryvegetationwithinandoutsideofthreedeerexclosuresonasingleslopewiththreelevelsofunderstoryvegetationcover:sparse(1%,exclosure'US'),moderate(30%,exclosure'MM'),anddense(80%,exclosure'LD')over10yearsaftera30%thinningofanold-growthcedarandcypressplantationwhichwasovergrazedbysikadeer.Results:Understoryvegetationcover,biomassandspeciesrichnessincreasedwithinandoutsidethe'US'and'MM'exclosuresafterthinning,andbiomasswasgreaterwithinthanoutsidetheexclosuresat10yearsafterthinning.Unpalatablespeciesdominatedboth'US'and'MM'exclosuresbeforethinning,andtreesandshrubsdominatedwithintheexclosuresovertimeafterthinning.Incontrast,unpalatable,grazing-tolerant,perennial,andannualspeciesincreasedoutsidethe'US'and'MM'exclosures.Nonoticeablechangeswereobservedwithinandoutsidethe'LD'exclosurewhencomparedwiththe'US'and'MM'exclosures.Conclusions:Ourresultssuggestthatthinningastandby30%basedonvolumeresultedinanincreaseinunderstoryvegetationcovermainlycomposedofbothunpalatableandgrazing-tolerantspeciesinaplantationforestwhereunderstoryvegetationissparseormoderateandsikadeerdensityishigh.Weemphasizethatestablishingdeerexclosuresorcontrollingdeerisessentialtomaintainingsimilarunderstoryvegetationbothwit