简介：为了确定黄土高原地区现有刺槐林改造的最佳间伐强度，１９９５年秋季对密度为２２２０株／公顷的９年生刺槐林进行了三种不同强度的间伐．通过间伐，降低了群落密度，减少了林冠截留率，增加了植树带内的汇流量，根系层内的土壤水分条件得到明显的改善．当间伐后的林分密度为１１１０株／公顷时，生长季内植树带土壤水分提高约４０％．随着间伐强度的增大，林木的水分生产函数曲线由直线上升变为以对数曲线上升；当间伐强度达到某一值时（保留密度为１１１０株／公顷），林木水分生产力随蒸腾量的变化曲线为抛物线．这表明此时水分已不再是林木生产的限制因子，在这种间伐强度条件下，单株林木和整个林分的水分生产力分别达到６０１７１ｇ·ｋｇ－１·ｍｍ－１和１４９７７７ｋｇ·ｈｍ－２·ｍｍ－１，因此将这一强度定为黄土高原地区刺槐林间伐的最佳强度．

简介：Invarioustemperatures,theeffectsofinorganicacidsonthefreephenollevelinliquefactionproductswereinvestigated.Inthispaper,thefreephenollevelwasusedasanindicatortoevaluateliquefactionefficiency.Resultsshowedthatsulfuricacidwasthebestamongthe4acids.Undertheconditionofreactiontemperature150oC,reactiontime1.5h,liquefactionratio(liquid/particleboard)4andcontentofsulfuricacid6%,thefreephenollevelintheliquefactionproductsofwasteparticleboardis36.95%,andthatoforiginalparticleboardis24.27%.

简介：应用根系喷雾箱（ＲｏｏｔＭｉｓｔｉｎｇＣｈａｍｂｅｒ，ＲＭＣ）形成的５次干旱循环，通过ＰＶ曲线的水分参数研究了多重复干旱循环对１年生北美短叶松ＰｉｎｕｓｂａｎｋｓｉａｎａＬａｍｂ．和黑云杉Ｐｉｃｅａｍａｒｉａｎａ［Ｍｉｌ］Ｂ．Ｓ．Ｄ．苗木耐旱特性的影响．结果表明，生长在干旱沙地的深根性树种北美短叶松，其丧失膨压的相对含水量（８０７６％～８１４１％）和水势（（－１７４±０１０）ＭＰａ）都比较低，细胞弹性模量（５７３～６５２ＭＰａ）比较小，而束缚水含量（５２７２％～５４２６％）比较高，显示出它固有的强有力的忍耐脱水能力；但是在多重复干旱循环下它却不能进一步调节其渗透势和细胞弹性，而且其束缚水含量和吸水能力也有所下降．生长在湿润地区的浅根性树种黑云杉，虽然其丧失膨压的相对含水量（８３５３％～８５５０％）和水势（（－１６８±００３）ＭＰａ）比较高，细胞弹性模量（８６２～９６４ＭＰａ）比较大，束缚水含量（３６４４％～４６０５％）比较低，显示出较弱的耐旱能力，但是它在多重复干旱循环下却能提高其束缚水含量以改善原生质耐旱程度，降低细胞弹性以提高其吸水能力，调节其渗透势以保持较高的膨压．这表?

简介：Blacklocust(RobiniapseudoacaciaL.)wasthefirstNorth-AmericantreespeciesimportedtoEuropeatthebeginningoftheseventeenthcentury.Itiscommonlyplantedworldwidebecauseofitsadaptabilitytoenvironmentalstresses,itsvaluablewood,easypropagation,frequentandabundantseedproduction,excellentcoppicing,highseedlingsurvival,andrelativelyhighwoodyield.InEurope,RomaniaandHungaryhavethemosthighly-developedblacklocustgrowingtechniquesandexperiences.Asaresultofincreasinginterestinblacklocustinmanycountries,thisreviewaimstoprovideacomprehensiveoverviewofstate-of-the-artsiterequirements,propagation,improvementandmanagement(includinggrowthandyieldaswellasuseinenergyplantations).

简介：Canada'sborealforestrepresentsanimportantcontributoroftheworld'swoodsupplyindustry.However,maintainingorincreasingproductivityoftheborealforestmaybechallenginginareasdominatedbyforestedpeatlands.Moreover,sustainablemanagementoftheseforestsmustalsoconsiderotherimportantaspectsoftheforestecosystemsuchasbiodiversityandcarbonsequestration.Toaddresstheseconcerns,ecosystem-basedmanagementhasbeenimplementedinsomeCanadianjurisdictions,suchasinregionswherealargeportionoftheborealforestisdominatedbyforestedpeatlands.Theobjectivesofthispaperare(1)tosummarizeourcurrentunderstandingofhownaturaldisturbancesinfluencestanddynamicsandbiodiversityinforestedpeatlands,and(2)toreviewthemaindifferencesbetweennaturalandmanagedforeststandswithrespecttosoil.properties,standproductivity,understoryplantcommunities.Wealsodiscusshoweven-agemanagementregimesucceedsorfailstopreserveoldforestsandhowthislossaffectsbothforeststructureandhabitatdiversityatthelandscapelevel.Weconcludebyshowinghow,inborealforestedpeatlands,forestmanagementcouldcontributetocarbonsequestrationandmitigateprojectedclimatechange.

简介：Ｓｅｌｆ－ＨｅｌｐＤｅｖｅｌｏｐｍｅｎｔ，ＳｕｓｔａｉｎａｂｌｅＭａｎａｇｅｍｅｎｔａｎｄＵｓｅｏｆＦｏｒｅｓｔｓａｎｄＴｒｅｅｓａｔｔｈｅＬｏｃａｌＣｏｍｍｕｎｉｔｙＬｅｖｅｌＴｈｅＦｏｒｅｓｔｓ，ＴｒｅｅｓａｎｄＰｅｏｐｌｅＰｒｏｇｒａｍｍｅＰｈ...

简介：Nonlinearmixedeffectsmodel(NLMEM)isbuiltontherelationshipofthefixedandrandomeffectsintheregressionfunction.TheNLMEMhasanobviouscomparativeadvantageinanalyzingthelongitudinaldata,repeatedmeasuresdataandmultileveldata.Two-levelNLMEMisusedtoanalyzethedominantheightforChinesefir(Cunninghamialanceolata).Theauthorsoutlinethetwo-levelNLMEMandintroducetheparametersestimationmethodofthemodel.BasedonfivecommonRichardandLogisticmodels,themixedmodelisbuilt.Themodelingdataareusedtocalculateandcomparewith19modelsderivedfromeachbasedmodel,and5optimalmixedmodelsarebuilt.Comparedthe5optimalmixedmodelswithtraditionalregressionmodels,itisshowedthatthetwo-levelNLMEMhasabetterfittingeffectthantheregressionmodel.

简介：Basedonamultilevellinearmixedmodelapproach,anindividualdiameterincrementmodelwasdevelopedforfirplantationtreesgrowinginJiangxiProvince.Thedatasetusedinthisstudycamefromlong-termpermanentresearchplots.Thedatabaseconsistsoftotalof82counties,365plots,5416treesand16248observations.Thepaperchosemixedeffectsmodelsinsteadofregressionanalysisapproachbecauseitallowsforpropertreatmentoferrortermsandcorrelationinarepeatedmeasuresanalysisframework.Themodelwasdefinedasamixedlinearmodelwithparameterrandomeffectofplot,areaorplotandareasimultaneous.Inadditiontheheteroscedasticityandcorrelationwastakenintoaccount.Mixedmodelcalibrationofdiameterincrementwascarriedoutwiththeindependentdatausingadifferentsampleofcomplementaryobservations.Theresultshowedthatthetotalstandbasalarea,thediameteroftargettrees,theratioofbasalareaoflargertreestotargettreediameter,andaltitudewerefoundtobesignificantpredictors.Boththefittingmodelandthecalibratedmodelmeanasubstantialimprovementcomparedwiththeclassicalapproachwidelyusedinforestmanagement.Aftertakingintoaccountreasonablevariancefunctionofheteroscedasticityandcorrelation,themodelshowsbetterofgoodnessoffitthanonlytakingintoaccountparameterrandomeffects.Thistypeofmodelingmethodologyshowsflexible,preciseandaccurate.