Multiple impacts of introduced deer on native forests in NW Patagonia, Argentina

RELVA, M. A.

Reserva Huilo-Huilo, Chile

Congreso; 7th International Deer Biology Congress; 2010

Fundación Huilo Huilo

Euro Asiatic deer were introduced in northwestern Patagonia ca. ninety years ago and among them red deer (Cervus elaphus) became invasive and currently inhabits forests, steppe, wet meadows and riparian habitats. I present the main results about direct and indirect effects of introduced deer as well as their synergistic effects together with other disturbances on forest communities. Also current knowledge gaps that should be filled for a better understanding of the relationship between introduced deer and native forests in northwestern Patagonia are identified. The studies were carried out on Isla Victoria, the largest island of Nahuel Huapi Lake, which is covered mainly by forests of southern beech Nothofagus dombeyi and conifer Austrocedrus chilensis with several subdominant tree species and dense understory vegetation. Additionally, Isla Victoria presents one of the oldest and largest histories of exotic plant and animal introductions in the area, which makes this island ideal for evaluating introduced deer and native forest interactions. Deer in forest areas in NW Patagonia seem to be intermediate feeders, being woody species the bulk of year-round diet, with graminoids and herbs increasing during spring and summer. The overall effect is that introduced deer at high densities alter the structure, abundance and composition of native forest communities. Dominance of spiny and non-selected species and the decrease of highly selected species characterize the understory. Exotic deer strongly inhibit growth in height of the native dominant conifer, Austrocedus chilensis, facilitating the invasion of the exotic conifer, Pseudotsuga mensiezii. By contrast, the impact of exotic deer on the abundance of seedlings and saplings of the dominant tree species is unclear, with much variation observed. Many of these impacted species are of ethnobotanical importance to the native Mapuche people, being mostly used for medicinal and food purposes. At ecosystem level the available evidence shows that after seven years of deer exclusion, there were not differences in physical, chemical and biological soil properties, likely due to the buffer effects of volcanic soils. In addition, introduced deer interact with natural and anthropogenic disturbances such as wind-storms, forest decline and salvage logging modifying plant succession. Much information about deer impacting forests in NW Patagonia comes from observational and comparative studies and to a minor extent from experimental studies. Furthermore, these studies were carried out in a few types of forest communities with high deer densities. Thus, further research requires more experimental studies involving a broader range of deer densities and diverse plant communities.