writing-TPO38综合写作阅读听力稿

TPO38阅读In1995amicroscopicfunguscalledphytophthoraramorum,orP.ramorum,wasfirstdetectedintheforestsofthewesternUnitedStates.P.ramoruminfectstreesandcausesparticularlyseriousdamageinoaktrees:inmanyinfectedoaks,leaveswitherrapidly,largecracksappearinthebark,andthetreesdie.AspreadofP.ramorumrepresentsaseriousthreattotheforestsinthewesternstates.Severalmethodsofprotectingtheforestshavebeenproposed.First,stoppingP.ramorumsporesfromspreadingwouldsurelybeaneffectivemethod.Sporesaresmallparticlesthroughwhichallfungi,includingP.ramorum，reproduce.ResearchershavediscoveredthatmanyP.ramorumsporescanbefoundalonghikingorbikingtrails,suggestinghuman-assistedspreadbywayofshoesandbicycletires.Afewmeasurestopreventsuchhuman-assistedspread-likeencouraginghikerstowashtheirshoesandinstallingnewbikescrubbersonbicycletrails-wouldbeaneffectiveandlow-costwaytostopthespreadofP.ramorum.Second,thereareafewfungicidal(fungus-fighting)chemicalsthatcanbeusedtoprotecttheoaktrees.Someofthesechemicalsstimulatetheoaktrees’naturaldefensesagainsttheP.ramorumfungusandhavebeenfoundinsmall-scaletryoutstosignificantlyreducethelikelihoodthattheoakswillbeinfected.AthirdwaytofightP.ramorumisapracticecalledclear-cutting.Thisapproachstartswithcuttingandburningthediseasedoaks,butitalsoinvolvescuttingandburningtheseeminglyhealthyvegetation(bushesandotherkindsoftrees)surroundingtheoaks.Thisisdonebecausesomeofthesurroundingplantsandtreesmaybeinfectedeventhoughtheydonotshowanysymptomsofthedisease.Cleaninglargerareasofvegetationinplaceswherediseasedtreesarefoundisoftenanefficientmeasuretostopthespreadofinfections.听力Unfortunately,themethodsdescribedinthepassagehaveseriouslimitationsthatmakethemineffectiveorimpracticalonmanysituations.Precautionslikecleaningshoesandusingbikescrubbersmighthelpalittle.Buttheymaynotmakeahugeimpact.TheproblemisthatP.ramorumsporesdidnotspreadjustthroughhumanassistance.Studieshavedetectedthesporesinwaterstreamsfollowingrainfall.Itappearsthatsporesarefrequentlypickedupbyrainwaterandwashedintowaterstreamswiththemcarriedalongdistances.Thistypeofwaterassistancespreadismuchhardertocontrol.Second,thefungicidereferredtointhereadingprovideeffectiveprotectionagainstPramorumonlywhentheyareinjecteddirectlyintotreetrunks.Buttheeffectlastonlyforfewmonths,sotheinjectionhavetoberepeated.Nowthistypeoftreatmentmightworkifyouwanttoprotectfewoaktreesinthecitypark.Butitjustnotverypracticalwhenprotectingwholeforeststhatcontainsthousandsandthousandsofoaktrees.Canyouimagineforestmanagershavetoinjecteverysingleoakinalargeforestwhendosefungicideeveryfewmonths.Thatsoundimpracticalandalsotooexpensive.Third,asthereadingexplains,clear-cuttingdestroythevegetationaroundthesickoaktrees,becausesomeofthatvegetationmaybeinfected.Butkeepinmind,someofthatsurroundingvegetationisinfacthealthy.Anditgetsdestroyedintheprocessanyway.Now,insomeforests,itmakessensetosacrificesomehealthyvegetationinordertostopthespreadofdangerousdisease;however,thevegetationinmanyforestsoftheUnitedStateincludetreespeciesthatveryrareandcannotgrowbackeasily.Soclear-cuttingintheseforestswouldmeandestroyingmanyhealthraretrees.ThiswouldrepresentthegreaterecologicaldamagethanthePramorumdamagetryingtoprevent.