Are invasive beavers the largest threat to sub-Antarctic forests in the Holocene? – a landscape-level analysis

ANDERSON, CB; VALENZUELA, A; WALLEM, PK; MARTÍNEZ PASTUR, G; LENCINAS, MV; SIMANONOK, MP

Mar del Plata

Conferencia; BIOLIEF 2011 - 2nd World Conference on Biological Invasions and Ecosystem Functioning; 2011

Universidad de Mar del Plata

South America’s sub-Antarctic ecoregion hosts the world’s southernmost forests and the largest extent of temperate ecosystems and ice fields south of the equator. Its remoteness kept it isolated from many modern environmental threats, including nutrient deposition and habitat fragmentation. Yet, the phenomenon of introduced species does affect this region; in the Fuegian Archipelago, the terrestrial mammalian assemblage is dominated 2:1 by exotics. The American beaver is believed to cause the largest impacts. To assess this assertion, we compared beaver’s effects on stream benthic richness, assemblage and biomass in natural lotic (forested and grassland streams) and lentic (bogs, lakes) habitats and compared them to disturbed habitats (streams affected by forestry management, beaver ponds and beaver meadows) at the habitat and landscape-scales by a) calculating the extent of invasion (% impacted stream length) and b) modeling natural and engineered landscapes for diversity and ecosystem function. Beavers invaded 30-50% of the streams, causing retention of organic material (+40-115%). At the patch-scale, exotic beaver impacts were predictable from studies in their native range (decreases in richness and increases in productivity). Timber harvesting with a riparian buffer had no detectable impact on benthos, while beaver invasion (ponds and meadows) significantly altered assemblages, but were not significantly different than those in natural lentic habitats, indicating that influence on assemblages at the landscape-scale was less. In contrast, the effect on stream function changed carbon dynamics. Since engineered patches were similar to natural habitats (bogs and lakes), beavers did not alter landscape-level community patterns, but affected ecosystem function.