Chapter8VariabilityofWoodWithinaSpecies 木材株内变异 Chapter8VariabilityofWoodWithinaSpecies 同种树木的变异性 Woodproducedbytreesofthesamespeciesisoftenmistakenlyassumedtobeidenticalinallstructuralandphysicalcharacteristics Infact differentpiecesofwood evenfromthesameteeeareneveridenticalandaresimilaronlywithinbroadlimits Alldimensionalandphysicalcharacteristicsofwoodwithintreesarevarible i e theyexhibitarangeodvalues Thevariationswhicharepresentcanberelatedtoradicaloraxialpositionofthesampleeitherwithinanindividualgrowthincrementoroveraseriesofgrowthincrementswithinthetree SummationofPrincipalFactorsAffectingVariavilityofWoodPropertiesinIndividaulTrees 影响单株树木木材性质变异的主要因子 A VariabilityinCellularCharacteristics 细胞特性的变异 Thecurvesrepresentingvariationincelldimensionsfrompithtobarkshowgreaterconsistencythanthoseforanyotherwoodcharacteristicwithintrees Thegeneralshapeofthesecurvesshowsminimumvaluesatorclosetothepith 髓心 Themagnitudeofthecelldimensionsincreasesintheearlyyearsnearthepithduringtheperiodinwhichmostofthecambialmaturation 形成层 occurs Asthecambiumbecomesphysiologicallymature theslopesofthecurvesrelatingcelldimensionstotheageofthecambiumbecomelesssteepormayshownochange Inoldagethsslopesofthecurvesmaydeclinewhenthecambiumagainproducescellswithreduceddimensions Thisgeneraltypeofpith to bark 从髓心到树皮 variationisparticularlyevidentforthoseaxialelementswhichundergopostcambialelongation Wherepostcambialelongationisconsiderable asinsoftwoodtracheidsandhardwoodfibers thecurvesexhibitsteepslopesnearthepith Fig7 5 Limitedpostcambialelongation asinvesselelements isreflectedintherelativelylowslopesofthecurvesnearthepith Tracheiddiameters 管胞直径 andcellwallthicknessinthesoftwoodsincreasefrompithtobarkbutwithmuchlesschangethanshownfortracheidlengths 管胞长度 Fig 7 8 Inthehardwoodsthepatternsofchangeinfiberdiametersandwall thicknessaregenerallysimilartothoseinsoftwoodsbutarelessconsistent Tracheidandfiberlengthswithingrowthincrementsincreasesfromthegroupupwardreachingamaximunbelowthecrown Lengthoftracheidsandfibersthendecreasestowardthetopofthetreetoaminimunmtypicalofthenewlyformedcambiuminthecrownregion Themaxiumtracheidsorfiberlengthintrunkoccursintheoutermostlayersofwoodatapointrangingfromone thirdtoone halfthetotaltreeheightabovetheground asisapparentinFig 7 6forsoftwoodsandinFig7 10forhardwoods Withinindividualincrements 年轮 thegeneralpatternisthatofaregularchangeinthelengthsofsoftwoodtracheids 管胞 hardwoodfibers纤维 andvesselelements 导管 intheradialdirectionfromearlytolatewood Theminimumlengthsarefoundintheearlywood andthemaximumisreachedinthelatewood BVariabilityinSpecificGravityandRelatedProperties 密度及有关性质的变异 1 Theradialdirection 横向 Averagespecificgravityinthemajorityofsoftwoodsshowsageneralincreasefrompithtobark Thisisrelatedtotheincreasingpercentageofdenselatewoodinsuccessiveincrementsfromthepithoutward Inthediffuse porous 散孔材 hardwoodsabouttwo thirdsofthespeciesstudiedexhibitincreasingspecificgravityfromthepithoutward whichappearstoberelatedtofibercharacteristics Inthering 环孔材 andsemi ring porous 半环孔材 hardwoodsdecreasesingspecificgravityfrompithtobarkcanberelatedtoincreasingearly woodpercentageinthesamedirectioninabouthalfofthespeciesstudied 2 Thelongitudinaldirection 树轴方向 Averagespecificgravityinthemajorityofthesoftwoodsdecreasefromthegroundupward Variationofspecificgravitywithheightwithinthetreeinhardwoodsfollowsbyoneofthethreepatterns itmaydecreasesupward itmaydecreaseinthelowertrunkandincreaseinthuppertrunk oritmayincreasefromthegroundupward C JuvenileandMatureWood 幼龄材与成熟材 Thestemofthetreemaybedevidedintotworegionsonthebasisfundamenttaldifferencesinthestructureandpropertiesofwood Juvenilewood 幼龄材 formsinacylindricalcolumnacoutthepithastheresultofprolongedinfluenceoftheapicalmeristemsintheregionoftheactivecrownonwoodformationbycambium Asthetreecrownmovesfatherupwardinagrowingtree theinfluenceoftheapicalmeristemsonagivencambialregiondecreasesandmaturewood 成熟材 isformed JuvenileandMatureWoodmustbeconsideredastwodistinctpopulationsinthesametree Thematurewoodpossessescharacteristicswhichareconsiderednormalforthespeciec whiclejuvenilewoodhasstructuralcharacteristicsandphysicalpropertiesinferiortothoseinthematurewoodofthesametree ThisisevidentforfiberandtracheidlengthsinFigs7 5and7 10 Itshouldbenotedthattheprimarybasisfordefiningjuvenileisthecellstructureandpropertiesofthewood Juvenilewoodinplantation grown 人工林 treescanberelatedtofastgrowthnearthepith butwideringsarenotnecessarilyassociatedwithjuvenilewoodinalltrees VariabtlityinWoodPropertiesamongTreesoftheSameSpecies 同树种木株间材性的变异 Variabilityinpropertiesofnormalwoodamongtreesofthesamespeciesmaybegreaterorsmallerthanthatwithinindividualtreesbeingcompared Thenormal woodcharacteristicsmaybemoditiedastheresultoflong termgrowingconditionsexistingondifferentsites eveninrathersmallareas Thedifferentconditionsondifferentsites eveninrathersmallareas Thedifferencesmayalsoarisefrominherentcharacteristicstransmittedfromparenttrees EnvironmentalandGeographicalInfluencedonVariabilityamongTrees 环境及地理因素引起株