title: Forest defoliator pests alter carbon and nitrogen cycles.
abstract: Climate change may foster pest epidemics in forests, and thereby the fluxes of elements that are indicators of ecosystem functioning. We examined compounds of carbon (C) and nitrogen (N) in insect faeces, leaf litter, throughfall and analysed the soils of deciduous oak forests (Quercus petraeaL.) that were heavily infested by the leaf herbivores winter moth (Operophtera brumataL.) and mottled umber (Erannis defoliariaL.). In infested forests, total net canopy-to-soil fluxes of C and N deriving from insect faeces, leaf litter and throughfall were 30- and 18-fold higher compared with uninfested oak forests, with 4333 kg C ha-1and 319 kg N ha-1, respectively, during a pest outbreak over 3 years. In infested forests, C and N levels in soil solutions were enhanced and C/N ratios in humus layers were reduced indicating an extended canopy-to-soil element pathway compared with the non-infested forests. In a microcosm incubation experiment, soil treatments with insect faeces showed 16-fold higher fluxes of carbon dioxide and 10-fold higher fluxes of dissolved organic carbon compared with soil treatments without added insect faeces (control). Thus, the deposition of high rates of nitrogen and rapidly decomposable carbon compounds in the course of forest pest epidemics appears to stimulate soil microbial activity (i.e. heterotrophic respiration), and therefore, may represent an important mechanism by which climate change can initiate a carbon cycle feedback.
authors.affiliation: Institute of Soil Science of Temperate and Boreal Ecosystems , Büsgen-Institute, Georg-August-University , Büsgenweg 2, 37077 Göttingen , Germany.
authors.forename: Anne
authors.identifier: 0000-0002-2754-2016
authors.initials: A
authors.lastname: L-M-Arnold
authors.affiliation: Institute of Soil Science of Temperate and Boreal Ecosystems , Büsgen-Institute, Georg-August-University , Büsgenweg 2, 37077 Göttingen , Germany.
authors.forename: Maren
authors.initials: M
authors.lastname: Grüning
authors.affiliation: Department of Biology , Plant Physiology and Biochemistry Group , University of Konstanz Universitätsstrasse 10, 78457 Konstanz , Germany.
authors.forename: Judy
authors.initials: J
authors.lastname: Simon
authors.affiliation: Institute of Soil Science of Temperate and Boreal Ecosystems , Büsgen-Institute, Georg-August-University , Büsgenweg 2, 37077 Göttingen , Germany.
authors.forename: Annett-Barbara
authors.initials: AB
authors.lastname: Reinhardt
authors.affiliation: Institute of Soil Science of Temperate and Boreal Ecosystems , Büsgen-Institute, Georg-August-University , Büsgenweg 2, 37077 Göttingen , Germany.
authors.forename: Norbert
authors.initials: N
authors.lastname: Lamersdorf
authors.affiliation: Natural Resources Research Laboratory , Bremer Str. 15, 29308 Winsen , Germany.
authors.forename: Carsten
authors.initials: C
authors.lastname: Thies
keywords: C- and N-cycle; climate change; defoliation; disturbance; forest pest; temperate forest