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Transcript
XVI ICSZ–InternationalColloquiumonSoilZoology SoilEcology–OralPresentations [TU_SE_O12] Earthworms in the Non-glaciated Americas: Intentional Introductions, Invasions, Soil Quality Indicators, and Interactions with Native Species MAC CALLAHAM1, GEORGE BROWN2, CARLOS FRAGOSO3, BRUCE SNYDER4, SAMUEL JAMES5 1 Center for Forest Disturbance Science, USDA Forest Service, Athens, GA, USA; 1Embrapa - Florestas, Colombo, PR, Brazil; 3Instituto de Ecologia, Xalapa, Ver., Mexico; 4Division of Biology, Kansas State University, Manhattan, KS, USA; 5Department of Biology, University of Iowa, Iowa City, IA, USA Theproblemofintroductionof,andsubsequentinvasionby,nonͲnativeearthwormspeciesis global in scope, and is the subject of some recent debate. On one hand, earthworms are consideredtobeindicatorsofgoodsoilqualityduetotheirpositiveeffectsonwaterrelations, nutrientavailability,etc.,butontheotherhand,introducedearthwormsdonotalwayshave strictlypositiveeffectsontheecosystemstheyinvade.Therehavebeenmanyintentionaluses of nonͲnative earthworms to realize benefits in agricultural, waste management, and bioremediationcontexts.LargescaleintroductionsofEuropeanearthwormshavebeenusedin AustraliaandNewZealandandthesepracticesarestillpromotedasawaytoimprovepasture productionandsoilcharacteristics.Likewise,nonͲnativeearthwormsarewidelyemployedfor managing organic wastes and subsequent production of vermicompost for horticultural or agricultural uses. Finally, nonͲnative earthworms have been employed as agents of soil restoration in petroleum contaminated soils, and in soils that have otherwise been severely disturbed.Inspiteofthisevidencethatintroducedearthwormscanperformcriticalanduseful functionsinsoil,therearestillmanysituationswheretheirpresenceisconsideredundesirable or even detrimental. For example, it has been demonstrated that the peregrine tropical speciesPontoscolexcorethruruscannegativelyaffectsoilphysicalcharacteristics,particularly whenthereisinsufficientorganicmatterinsurfacehorizonsofthesoil.Additionally,thereis growing evidence that nonͲnative earthworms interact negatively with native litter and soil biota, and there have been suggestions that invasive earthworms can competitively exclude native species. Thus, one unresolved issue is how introduced earthworms influence soil processes when they invade soils that already support native earthworm species. Here we present examples from North, Central, and South American soils to examine relationships between land management and the composition of earthworm communities. A general pattern emerges suggesting that past disturbance and disturbance intensity can be a strong determinant of nonͲnative earthworm representation in the total community, and this has implicationsforlandmanagersfocusedonconservationandrestorationobjectives. Ǧ97Ǧ