简介：Determiningthephysicalandmechanicalpropertiesofsoilanditsbehaviorforengineeringprojectsisessentialforroadconstructionoperations.Oneofthemostimportantprinciplesinforestroadconstruction,whichisusuallyneglected,istoavoidmixingorganicmatterwithroadmaterialsduringexcavationandembankmentconstruction.Thecurrentstudyaimedtoassesstheinfluenceoforganicmatteronthephysicalpropertiesandmechanicalbehaviorsofforestsoilandtoanalyzetherelationbetweentheamountoforganicmatterandthebehaviorofforestsoilasroadmaterial.Atypicalsoilsamplefromthestudyareawascollectedbesideanewlyconstructedroadbed.Thesoilwasmixedwithdifferentpercentagesoforganicmatter(controltreatment,5,10,and15%bymass)anddifferenttestsincludingAtterberglimits,standardcompaction,andCaliforniabearingratio(CBR)testswereconductedonthesedifferentsoilmixtures.Theresultsshowedthatsoilplasticityincreasedlinearlywithincreasingorganicmatter.Increasingtheorganicmatterfrom0%(control)to15%resultedinanincreaseof11.64%oftheplasticlimitand15.22%oftheliquidlimitafterdryingat110℃.Also,increasingtheorganicmattercontentreducedthesoilmaximumdrydensityandincreasedtheoptimummoisturecontent.Increasingtheorganicmatterfrom0to15%resultedinanincreaseof11.0%oftheoptimummoisturecontentandadecreaseof0.29g/cm3ofthemaximumdrydensity.OrganicmatterdecreasedtheCBR,whichisusedastheindexofroadstrength.Adding15%organicmattertothesoilresultedinadecreaseoftheCBRfrom15.72to4.75%.Therewasasignificantdifferencebetweenthetwodryingtemperatures(60and110℃)forthesameorganicmattermixtureswithlowerwatercontentvaluesafterdryingat60℃.Theresultsrevealedtheadverseinfluenceoforganicmatteronsoilengineeringpropertiesandshowedtheimportanceoforganicmatterremovalbeforeexcavationandfillconstruction.

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