Invasive North American beaver alters greenhouse gas fluxes in sub-Antarctic riparian forests

Abstract The North American beaver ( Castor canadensis ) has become a major invasive threat in the sub-Antarctic forests of the Fuegian Archipelago. By constructing dams, beavers flood and kill extensive forest areas, convert riparian forests (RFs) into wetlands, and substantially alter hydrological and biogeochemical processes. This study presents an integrated austral summer assessment of greenhouse gas(GHG) fluxes in a beaver-created wetland and an adjacent intact RF. Fluxes were measured from water, soil, and tree stem surfaces. CH 4 emissions were markedly higher in the beaver-degraded area than in the intact forest, with total ecosystem emissions of 20.36 and −1.59 mg CH 4 m −2 d −1 , respectively. In contrast, CO 2 emissions were greater in the intact RF (39.3 g CO 2 m −2 d −1 ) than in the beaver-degraded forest (4.32 g CO 2 m −2 d −1 ). Annualizing these summer fluxes yielded total GHG emissions that were 179 t CO 2-eq ha −1 yr −1 higher in the intact forest than in the beaver-created wetland. However, this difference does not account for forest gross primary production, which was not measured and for which no comparable estimates are available for sub-Antarctic forests. Consequently, although the intact RF likely functions as a net carbon sink, its magnitude could not be reliably estimated. In contrast, the beaver-created wetland, devoid of living trees, remained a net source of approximately 17 t CO 2-eq ha −1 yr −1 . These results indicate that beaver-induced deforestation may represent a substantial source of GHGs in southernmost forest ecosystems.