POLICYBRIEFStudyonBenefitofEnvironmentalfriendlyRubberPlantationDisclaimer:thisversionisadirecttranslationoftheoriginalChineseversionBulletinonLancang-MekongEnvironmentalCooperationTheRenaissanceofNaturalRubberAsakindofrubberyieldingtreeplantedinalargescalearoundtheworld,theheveabrasiliensishastheadvantagessuchashighyield,goodquality,longeconomiclife,easylatexexploitation,andfastlatexregeneration.OriginatinginthetropicalrainforestinAmazonBasininSouthAmerica,duringtheprocessofevolutionforthousandsofyears,theheveabrasiliensisformstheuniquehabitofadaptationtohigh-temperature,high-humidityandcalmwindenvironmentgradually,hasthephysiologicalcharacteristicsofrapidgrowth,sensitivereactiontolowtemperature,undevelopedwoodandmechanicaltissue,fragiletrunkvulnerabletowinddamageattacks,andhashigherrequirementfororganicmattercontentofthesoil.Duetosuchcharacteristics,therubbertreesareplantedinalimitedareaaroundtheworld.Atpresent,undertheconstraintsoftheplantingconditions,90%oftherubbertreesintheworldaremainlyplantedinThailand,Indonesia,Malaysia,VietnamandotherSoutheastAsiancountries,aswellasafewAfricancountriessuchasNigeria,indicatingthatthenaturalrubberisatypicalenvironmentalconstraintresource.

Byplantingofthenaturalrubber,itispossibletonotonlymeetthedemandsforrelevantproductsinproductionandlife,butalsoenhancetheincomeoffarmers,increasetheemploymentopportunities,andimprovelivelihoodstoagreatextent.However,itisanindisputablefactthattheplantingofthenaturalrubberleadstotheproblemsinlandoccupationandfoodsecurity;furthermore,ithasoutstandingnegativeimpactontheecologicalenvironment,suchaslossoftropicalrainforest,reductioninbiodiversity,soilerosion,anddecreaseinsoilfertility.Rubberplantationhasapreferentiallynegativeneteffectonecosystemfunctionswhencomparedtoadjacenttropicalforest(Singhetal.,2021)2BulletinonLancang-MekongEnvironmentalCooperationBackgroundofconstructionofenvironmentalfriendlyrubberforestThemonocultureofrubbertreesinlargearealeadstoaseriesofproblemsinecologicalenvironment,suchas:DecreasedsoilfertilityTherearefewundergrowthvegetationlayersandfewlitterspeciesintherubberforest.Comparedwiththetropicalrainforest,therubberforesthaspoorsoilfertility.Fromtheperspectiveofnutrientretentionbenefit,thatofthetropicalrainforestis2.11timesasmuchasthatoftherubberforest.Thesoilqualitywillbedegradedtocertainextentifthenaturalforestisconvertedintotherubberforest.Themonocultureandtappingoftherubberforestwillalsocausethelossofsoilnutrientseasily.ReducedbiodiversityDuetotheobviousvegetationstratificationandtherichspecies,thebiodiversityandthegermplasmgenebankareestablishedinthetropicalrainforest;however,duetothesimplestructureofthecommunity,thediversityandthestabilityofspeciesintherubberforestaredestroyed.Thelarge-scaleplantingoftheheveabrasiliensisleadstothesignificantdeclineinthecoveragerateofthetropicalrainforest,thedestructionofthehabitatenvironmentofanimalsandplants,thedegradationofecologicalenvironment,andthereductioninbiodiversity.Comparedwithnaturalforest,thenumberofbirdsinthepureartificialrubberforestdecreasesbyatleast70%,andthenumberofmammalsdecreasesbyatleast80%.

Sharpdeclineintropicalrainforest,lossofbiodiversity,andfrequentoccurrenceofplantdiseasesandinsectpests(Lietal.,2007;GuanZhibinetal.,2005;LiJiazhietal.,2008).Severesoilerosion,changeinphysicalandchemicalpropertiesofsoil,anddecreaseinsoilfertility(WangHuihaietal.,2003;PangJiaping,2009;Yangetal.,2004).Poorwaterconservationcapacityofrubberforest,andshortageofwaterinrubberplantingarea(Tanetal.2011;ZhouWaietal.,2011;ZhouZongandHuShaoyun,2008)Changesinlocalclimate:Decreaseinnumberoffoggydays,reductionindurationofthickfog,anddeclineintherelativehumidity(YuYanetal.,2007;DaiBo,2008;Liuetal.,2007).3BulletinonLancang-MekongEnvironmentalCooperationDecreasedwaterconservationcapacityAfterthetropicalrainforestisconvertedintorubberforestbycuttingdown,undertheinfluenceofaggravatedsoilerosion,thesoillayerbecomesthinner,thewaterretentioncapacityandwaterstoragecapacityofthesoilaredegraded,thepermeabilityofthesoilisreducedtocertainextent,andthewaterconservationfunctionofthesoilisdecreased.Attheannualscale,theevapotranspirationoftherubberforestislargerthanthatofthetropicalrainforest,andthewaterstoredintherubberforestintherainyseasonisnotsufficienttosustainvigorousevapotranspirationinthedryseason,resultingintherunoffoftherubberforestlessthanthatofthetropicalrainforestinthedryseason.Ifalargenumberoftropicalrainforestisreplacedbythesinglerubberforest,theactualrepellencyofsoilintherubberforestishigherthanthatinthetropicalrainforest,resultinginserioussoilerosionintherubberforest,whilethetropicalrainforestwithgoodvegetationandcomplexstructurehaslittleimpactonsoilerosion.AggravatedplantdiseasesandinsectpestsTherapidincreaseinplantingareaandtoosimpleplantingstructureoftherubberforestprovidesufficientspaceforpeststosurviveanddevelop,butthereisnosuitablehabitatfornaturalenemiesofpests,soitiseasyforpestpopulationsto“avoidnaturalenemies,anddevelopandgrowstronger”.

Inaddition,theexcessiveuseofethephon(whichcanstimulatetheyieldofrubber)bytherubberfarmers,evenexceedingthesafetythreshold,resultsinthereductioninresistanceoftherubberforestinthelargearea,thedeclineintheyieldofrubber,andtheearlyoccurrenceofdeclineofrubbertrees,whicharethedominantfactorsforseriousdamagecausedbycambiumbeetle.FragmentationoftropicalrainforestlandscapeMoreandmorerubberpatchesaregraduallyreplacingothertypesofpatches,leadingtotheconvergentdevelopmentoflandutilizationintherubberplantingarea.Forexample,inXishuangbanna,thesteepslopeandlow-grassshrublandatahighaltitudeofabout1,200mareevolvingintotherubberforestquickly,andthesporadicdistributionofthepatchesincreasesthefragmentationdegreeofthelandscape.Basedontheanalysisoftheecologicalquantitativeindicators,itcanbeseenthatrubberhasformedtheregionalcharacteristicssuchashighcontrast,segmen-tationandfragmentation.Thesegmentationandfragmentationofthetropicalrainforestlandscapeecosystemwillaffectthematerialcycle,energyflow,andspeciesflowintheecosystem.Thedeclineinlandscapedomi-nanceindexandtheincreaseinfragmentationmeanthattheoriginallandscapedominanceoftropicalrainforestinthisregionisnolongerprominent,theserioussegmentationandfragmentationhaveoccurred,thehierarchicalstructureofthetropicalrainforesthasundergonethequalitativechange,andthesuccessionandrestorationcycleofthenaturalvegetationnolongerexists.4BulletinonLancang-MekongEnvironmentalCooperationIntensifiedhuman-animalconflictWiththerapidgrowthofpopulation,thespaceofpopulationmobilityintherubberplantingareaisincreasinggradually,andtheareacoveredbycropsandtheconstructionareaoftheinfrastructurearealsoincreasinggradually,exertingcertainimpactonthewildnaturalresourceareas.Mostwildspecies,suchastheAsianelephant,tendtobefoundinthetropicalrainforestthatissuitableforrubbercultivation,butduetothegradualdecreaseintheareaofthetropicalrainforest,thelivingspaceofthe

wildAsianelephantisreducedtoagreatextent.Especiallyinrecentyears,astheplantingareaoftherubberasaneconomiccropincreasesgradually,andthemaximumaltitudeforplantingoftherubberalsoincreases,resultinginmoreoverlappingbetweentherubberplantingareaandthelivingareaofthewildspeciesarea.Thisnotonlyleadstodamageoftheeconomiccrops,alsoruduceslivingareaofthewildspecies,resultinginthehuman-animalconflict.Inadditiontotheenvironmentalimpact,therubberindustryitselfcannotbe“immune”.Theenvironmentalproblemscausedbythelarge-scaleplantingofthesinglerubberwillinturnaffectthesustainabledevelopmentoftherubberindustry.5BulletinonLancang-MekongEnvironmentalCooperationExplorationonplantingmodelandbenefitofenvironmentalfriendlyrubberforestAccordingtotheprinciplesofecologyandeconomics,bycertainbiological,ecologicalandengineeringtechniquesandapproaches,itispossibletoestablishthemultilayerandmultiple-speciescompoundecosystemofrubberforest,whichisakindofhigh-efficientartificialecosystemwiththestructureand

functionsachievingastablestateofdynamicbalance,andwiththeimpactonenvironmentfallingwithintheresourcesupplycapacityandtheenvironmentalself-purificationcapacityofitssystem.Thiscompositeecosystemcanachievetheeconomicyieldofrubberwithoutobviousadverseimpactontheenvironment.Schematicdiagramillustratingtheeffectofrubber-basedagroforestryonsoilphysico-chemicalpropertiesofrubberplanting(Chenetal.,2019)6BulletinonLancang-MekongEnvironmentalCooperationThecommonlyusedenvironmentalfriendlyrubberforesttransformationmodelsincludethejungle-typerubberforesttransformationmodeandtheagroforestryrubberforesttransformationmode.Jungle-typerubberforesttransformationmodeThejungle-typerubberforest,asakindofcompoundrubberplantingmodeconstructedbyimitatingthestructureoftropicalrainforest,isabalancedanddiversifiedplantingmode,meaningtheplantingoftheartificialforestdominatedbyheveabrasiliensisonthefallowland.Theannualyieldofrubberinthejungle-typerubberforestisapproximately640kg·hm-2,andtheincomefromrubberyieldaccountsforapproximately60%ofthetotalincomefromtheforest.Inthejungle-typerubberforest,theincomebeforetherubbertappingperiod(approximately7years)canbegainedbytheothergrainsandcrops,andthemainincomegainedbytherubberfarmersinthelaterstagecomesfromrubber.Otherplantsgrowingnaturallyintherubberforestcanprovidefruits,fuelwood,woodandotherresources,whicharemainlyusedbyfarmersforself-sufficiencyandalmostrequirenolaborinput.Thisplantingpatternisfriendlytosmall-scalefarmers,becauseitcannotonlymeettheneedsofthegrowingpopulationforeconomicgrowth,butalsoprotectthepreciousforestenvironment.

AgroforestryrubberforesttransformationmodeAsanimportantmeasuretoincreasethebenefitoftherubberplantationrapidlyandeffectively,theintercroppingofrubberplantationcanincreasetheyieldoftherubberplantationtoagreatextent.Atpresent,theintercroppingofrubberplantationiscarriedoutmainlyintheyoungrubberplantation.Duringthesaplingperiod,mostcropscanbeintercropped,whileonlyafewshade-tolerantcropscanbeintercroppedaftergrowingup,sotheintercroppingcycleisshort.Therubberyieldoftherubberplantationinwhichtheplantingmodeisadjustedandthewide-narrowrowplantingisadoptedissimilartothatofthetraditionalrubberplantation.Aftergrowingup,morecropscanbeintercropped,sotheintercroppingproductionisallowedduringthewholeproductioncycle.Moreandmorerubberplantationswiththewhole-cycleintercroppingmodeareused.7BulletinonLancang-MekongEnvironmentalCooperationInadditiontoeconomicbenefits,theenvironmental-friendlyrubberforestcanalsoproducethefollowingecologicalbenefits:ToimprovethemicroclimatecharacteristicsofthecompoundsystemThesuitableintercroppingcompoundeco-systemcanimprovethemicroclimateintheeco-environmentoftherubberplantation.Insummerandautumnatthehightemperature,itcanreducethetemperatureofnear-groundairandsurfacesoilsignificantly,reducetheevaporationofsoilmoisture,andincreasetheairhumidity,soastomitigatethedamageofhightemperatureanddroughttoheveabrasiliensis.Duetotheimprovedmicro-growingenvironmentofheveabrasiliensis,andtheincreasedphotosyntheticefficiencyandthelightenergyutilizationrateofheveabrasiliensis,thestemdiameterofheveabrasiliensis,especiallyyoungheveabrasiliensis,alsogrowbetter.Toconservewaterandsoil,andimprovesoilefficiencyTheeffectofintercroppingsystemofrubberplantationonsoilandwaterconservationandsoilimprovementhasbeenverifiedbyagreatnumberofresearches.Incaseofthedownslopeplantingandthecrossslopeplantingforintercroppingofpineappleintheyoungrubberforest,thetotalrunoffisreducedby1403.23m3/hm2and2580.47m3/hm2,andthetotalerosionamountisreducedby560kg/hm2and769kg/hm2,respectivelycomparedwiththoseoftherubberforestwithoutplantingofthepineapple.Thetotalrunoffandthetotalerosionamountinthecrossslopeplantingarelowerthanthoseinthedownslopeplantingto

agreatextent.Byintercroppingcinnamonintherubberplantation,itispossibletoavoidthedirectimpactandscouringofrainwateragainstthetopsoil,slowdownsurfacerunoff,andpromotetheinfiltrationofrainwaterintothesoillayer,soastopreventthesoilerosionintherubberplantationandincreasethewaterstorageinthesoillayer.Furthermore,itisfoundthattheintercroppingcanincreasethesoilavailablenutrients,improvethesoilstructure,andimprovethesoilfertilitytoagreatextent.ToimprovethebiodiversityandstabilityofthesystemWithmultiplecomponents,complexsystemstructure,andgoodecologicalenvironment,itispossibletoimprovethebiodiversityoftheintercroppingcompoundsystemintherubberplantation.Thenumberofbirdsrecordedintheenvironmental-friendlyecologicalrubberplantationismuchmorethanthatrecordedinthepurerubberforest,andthehabitatselectedbybirdsshowsthecharacteristicsofforestthicket>nearshorewaterarea>environmental-friendlyecologicalrubberplantation>pureforest.Inthesoillayerwiththedepthof0-10cm,theamountofrootsinthesolecroppingrubberplantationislesscomparedwiththatintheintercroppingrubberplantation,soastoprovideenoughspaceforthesurvivalandreproductionofsoilanimals.However,withinthescopeofintherubber-teacommunityforest,mostoftherootsoccupiesthesoilspace,leadingtothedecreaseinthenumberofsoilanimals.Thetermiterichnessin8BulletinonLancang-MekongEnvironmentalCooperationtheagroforestryplantingmodedominatedbyrubberishigherthanthatofthesolecroppingrubberplantation,playingapositiveroleintheconservationoftermitedi