Impact of Cervids on Biodiversity, Ecosystem Processes and Wildlife

Abstract

The populations of large herbivores have increased considerably the last decades in several regions in the northern hemisphere, and possible negative effect on the ecosystem due to “overabundance” of cervids is today a serious concern in the Nordic countries as well as in North America and Japan. In the Nordic countries the populations of cervids like moose and roe deer have increased considerably to densities probably not experienced in post glacial times. Their browsing in young forest stands causes considerable economical losses for forestry. However, today focus is also on indirect effects of their browsing, and possible negative effects on biodiversity and fundamental ecosystem processes like soil nutrient cycling. Against this background a new project was initiated 1999. The objectives are to experimentally study impact of different moose densities on plant productivity, biodiversity and ecosystem processes (especially soil processes) in young forest stands situated along a habitat productivity gradient. The objective is also to study if the indirect effects on soil processes can feed back on the plant productivity and ultimately the herbivore population dynamics. The study is done by simulating browsing, defecation and urination corresponding to different moose densities in exclosures situated along the productivity gradient. A fully experimental study of several known herbivore densities where also underlying environmental variation is taken into account are rare in forest ecosystems, and offers the opportunity to detect non linear responses as well as reveal underlying mechanisms. The results show that moose can be a major driver of ecosystem change. Impact on biodiversity and ecosystem processes (especially soil processes) is strongly dependent on moose density and interactions between moose density and habitat productivity are common. Several studies reveal a positive effect of moose at moderate densities and a strongly negative at higher, i.e. non linear responses. The negative impacts often decrease as habitat productivity increase and can even be reversed along the productivity gradient. The project is intended to be a long term study, and the study sites will now go into the recovery phase when the experimental treatment (i.e. simulation of browsing, defecation and urination) is finished. The future objective is thus to study ecosystem recovery and resilience.

Inga-Lill Persson
Department of Animal Ecology, Swedish University of Agricultural Sciences
SE-90183 Umeå, Sweden