PARENT SESSION
Poster Session 20: Invasive Species
Wednesday, August 10, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal
Exotic beavers increase native and exotic riparian plant richness and decrease forest regeneration in Cape Horn County, Chile.
Anderson, Christopher*,1, 2, Rosemond, Amy1, Griffith, Clayton1, Rozzi, Ricardo2, 3, 4, 1 Institute of Ecology - University of Georgia, Athens, GA2 Omora Ethnobotanical Park, Puerto Williams, Chile3 University of North Texas, Denton, TX4 Universidad de Magallanes, Punta Arenas, Chile
ABSTRACT- The North American beaver (Castor canadensis) was introduced into the Argentine portion of Tierra del Fuego Island in the 1940s and since has colonized large areas of the archipelago in both Chile and Argentina. The beaver alters both ecosystem structure and function in its native habitat by increasing species and habitat diversity, changing nutrient cycling and enhancing retention and resistance to disturbance. We quantified the introduced beaver's impact on riparian plant species richness, assemblage and forest regeneration, comparing naturally forested riparian zones to beaver-created meadows on Navarino Island, Chile (55°S). Beavers decreased tree canopy cover to 30 m away from streams in meadow habitats. Additionally, beaver activities decreased overall tree regeneration and changed assemblage by suppressing Nothofagus betuloides and N. pumilio seedlings and permitting N. antarctica establishment. Herbaceous species richness per 0.5 m2 survey plot nearly doubled in beaver meadows, compared to forests, due in part to facilitating exotic species in meadows. Total richness of exotic plants increased from 1 species in forested sites to 10 species in beaver meadows, and abundance also rose with introduced species being found in 2.5% of forested survey plots and 53.8% of meadow plots. The beaver's modifications did create significantly distinct plant assemblages (Morisita-Horn Similarity Index), but substantial overlap occurred with 42% of species shared in common between both habitats and only 4 species being unique to forests. The consequences of these assemblage alterations include changes in function associated with forest vs. meadow habitat and the spread of invasive plants, which in this area are typically localized along the human disturbed coast. The creation of invasion pathways by beavers along waterways towards the interior of islands, therefore, threatens one of the world's largest and most pristine temperate forest ecosystems.
Key words: Castor canadensis, Invasive, Sub-Antarctic, Nothofagus