Document: JOH-3-42-6

Effects of summer grazing by reindeer on composition of vegetation, productivity and nitrogen cycling.

OLOFSSON, J.* ¹, H.KITTI ², P.RAUTIAINEN ², S.STARK ² and L.OKSANEN ¹

University of Umeå, Sweden ¹
University of Oulu, Finland. ²

Abstract:
We investigated the effect of reindeer (Rangifer tarandus) grazing on vegetation structure, primary production and nutrient cycling of tundra heath vegetation in northern Norway. Fences, erected 30 years ago, allowed us to compare winter grazed, lightly summer grazed and heavily summer grazed vegetation at four different sites. At two sites, graminoids dominated the heavily grazed zone completely, while ericoid dwarf shrubs had almost disappeared. In the other two areas, the increase of graminoids was almost significant. The vegetation was analysed with a point frequency method. We measured primary production and nitrogen cycling in one site. Primary production was measured by harvesting annual shoots of all plants. The primary production was highest in the heavily summer grazed zone and lowest in the lightly summer grazed zone. This is the first evidence that grazing may increase the productivity in the tundra. The increased productivity in the heavily grazed zone is probable caused by an increased soil nutrient cycling as initial NH₄ and organic N content were significant higher and the lag time was significant shorter even if there was no significant difference either in gross or net mineralisation. These results were inconsistent with the view that the highest productivity is found at intermediate grazing pressure. These results rather support the hypothesis that intensive grazing can promote a transition of moss-rich heath tundra into productive, graminoid-dominated steppe-like tundra vegetation. Moreover the results suggest that intermittent intensive reindeer grazing can enhance productivity of summer pastures.

Keywords: reindeer, herbivory, primary production, nutrient cycling

This abstract is being presented at: 3:30 PM in session:
Oral Session #17: Mammalian Herbivory.