Agroecology: modelling the resilience of agro-ecosystems ... › IMG › pdf › cours2.pdf ·...
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Agroecology:modellingtheresilienceofagro-ecosystems.Cours2CorinneRobert(INRA,ENS)andDavidClaessen(ENS)
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Characteris9csofnaturalecosystems,tradi9onalandmodernagriculture
2Malézieux,2012
Whatisbiodiversity?
GENES
SPECIES
FUNCTIONS
Diversityof:
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SoilferClity
Waterquality
Nutrientcycling
CarbonsequestraCon
Pathogentransmission
PollinisaCon
Fossileenergy
Naturalresources
Pharmacology
Epidemicrisk
TrophicinteracCons
PrimaryproducCon
Watercycle
Geochemistry
Solstability
Airquality
AgriculturalproducCon
ClimateregulaCon
ResistancetoinvasionofexoCcspecies
Ecosystem“func9ons”and“services”
GENES
SPECIES
FUNCTIONS
“FUNCTIONS”
“SERVICES”
Diversityof:
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Agroecology:modellingtheresilienceofagro-ecosystemsCorinneRobert(INRA,ENS)andDavidClaessen(ENS)
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Whatisagroecology?• Asocialmovement
– Focusontropicalcountries– Smallscale,tradiConalagriculture– FocusonsocialjusCce,roleofmulCnaConalsinworldinequaliCes,peasantindependence
– ConservaConofbiodiversity,culturaldiversity– AlternaCveeconomical,societalsystem,humanwellbeing
• AnagriculturalproducConsystem– UsecologicalprocessestoimproveproducConandreducedependenceonpesCcidesandferClizers
• AscienCficdiscipline– Howtodesignsustainableagriculturalsystemsusingecologicalprinciplesandknowledge?
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Whatarethescien9ficprinciplesunderlyingagroecology?
• Useecologicalprocessestoimproveagriculturalperformancewhilereducingenvironmentalimpact
• Biodiversity:insteadofusingmonocultures,usemixturesofspeciesandvarieCes
• UseecologicalinteracConsbetweenspeciestoregulatepests
• UseecologicalprocessestoimprovesoilcharacerisCcs
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Diversity,complexity,recycling,self-regulaCon(resilience?)
“Agroecology”Naturalecosystem Modernagriculture
Bohanetal2013• Mimicryofnaturalecosystems:
– notexpectedtoprovidetheyieldsobtainedinmodernagriculture,
– Keyecologicalconceptsinnaturalsystems• resilience,stabilityandcapacityforself-organizaCon
– notnecessarilyreadilytransferableorrelevanttoagroecosystems(Malézieux,2011).
• Somekeyecologicalprinciplesshouldholdinagroecosystems– maintainingdiversecomplementaryfuncConaltraitsinspeciesassemblages,
– forsustainingthe‘predictable’assemblyofcommuniCesofspeciesaroundacrop
– forthemanagementofthemicrobial,plantandanimalspeciesnaturallypresentinthesystem.
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Biologicalcontrol
• NaturalenemiesofagriculturalpestsmaybeusedtolimitpestdensiCesbeloweconomicthresholds(Costanzaetal.,1997).
• SuchregulaConshouldallowpesCcideinputstobereducedandsystemresilienceandsustainabilitytobeenhanced.
• UnderwhatcondiConsdoweexpectbiologicalcontroltobeeffecCve,andinwhattypeofnetworkstructure?
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Commonprinciplesinagroecology
• Highbiodiversity(polyculture)
• Combininganimalhusbandryandcrops
• SCmulateacCve,alivesoils
• OpCmizespaCalorganizaCon(landscape)
- OpCmaluseofsoilnutrients- PosiCveeffectonhydrology- Bufferagainstunfavorable
condiCons
- FerClizaCon- Weedcontrol- Herbivorecontrol
- NitrogenfixaCon- Nutrientrecycling- Favorablehydrology
- Reducepestanddiseasedispersal- Reducewinddamage- Reducesoilerosion
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“Tradi9onal”vs“Agroecological”view
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Examplesofagroecologialsystems
MiguelAlCeri 13
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Achievinggoodweedsuppressionwithcovercropmixtures.
ThelegumesredcloverandAustrianwinterpeaareslowertoestablishinthefallandcanallowweedstogetafoothold(A,B).
Undernitrogen-deficientcondiCons,canolagrowthislimited(C),reducingitsweedsuppressioncomparedtocanolawithsufficientnitrogenavailable(G).
Amixtureofslow-growinglegumes(D)willbenobeieratsuppressingweedsthanaslow-growinglegumemonoculture.
Grasseslikeoatsandryeareexcellentweedsuppressors(E,F)butevenasmallgapbetweendrillpassescancreateaspotforweedstotakeroot(F).
Adiversemixturethatincludesafewfast-growingspecieswillprovideweedsuppressionwhileallowingforbenefitssuchasnitrogenfixa9onandfloralresourcesfromtheotherspecies(H).
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Complementarygrowthforms:- cerealryeandcanolatransiConfromshortdensecanopiestotallopen
canopiesinthelatespring,- Austrianwinterpeaisvining,andredcloverremainsshortanddense.
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Agroecology:modellingtheresilienceofagro-ecosystemsCorinneRobert(INRA,ENS)andDavidClaessen(ENS)
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Ecologicalnetworktheory
• Bohanetal2013– eveniftheprovisionofaspecificecosystemservicesmaybemaximizedthroughtheabundanceoffuncConallyimportantspecies(Gaston,2010),suchashoneybeesaspollinators(Calderone,2012;Hagenetal.,2012),
– widersystemresilienceandecosystemserviceprovisionreliesdirectlyonspeciesdiversityandfuncConing(Naeemetal.,2009).
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“Resilience”thoughbiodiversity(1)
• “AresilientagroecosystemwillconCnuetoprovideavitalservicesuchasfoodproducConifchallengedbyseveredroughtorbyalargereducConinrainfall”
• TheroleofdiversityinagroecosystemstofuncConalcapacityandresilience(Vandermeerandcolleagues1998):– BiodiversityenhancesecosystemfuncConbecausedifferentspeciesor
genotypesperformslightlydifferentrolesandthereforeoccupydifferentniches
– BiodiversityisneutralornegaCveinthattherearemanymorespeciesthantherearefuncCons;thus,redundancyisbuiltintothesystem.
– BiodiversityenhancesecosystemfuncConbecausethosecomponentsthatappearredundantatonepointinCmemaybecomeimportantwhensomeenvironmentalchangeoccurs.
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“Resilience”thoughbiodiversity(2)
• Thekeyhereisthatwhenenvironmentalchangeoccurs,theredundanciesofthesystemallowforconCnuedecosystemfuncConingandprovisioningofservices.
• Theinsurancehypothesis(YachiandLoreau1999),whichproposesthatbiodiversityprovidesaninsurance,orabuffer,againstenvironmentalfluctuaConsbecausedifferentspeciesresponddifferentlytochange,leadingtomorepredictableaggregatecommunityorecosystemproperCes.
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