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

Abstract

In this study, we investigated the effect of reindeer grazing on tundra heath vegetation in northern Norway. Fences, erected 30 yr 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. At one of the sites where graminoids dominated the heavily grazed area, we also measured plant biomass, primary production and nitrogen cycling. In this site, heavy grazing increased primary production and rate of nitrogen cycling, while moderate grazing decreased primary production. 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 suggests that intermittent intensive reindeer grazing can enhance productivity of summer ranges.

Effects of reindeer density on vascular plant diversity on North Scandinavian mountains

“…Most of the reported effects of reindeer grazing are from winter-grazed or year-around grazed areas, but reindeer also influences the vegetation in summer-grazed areas (Oksanen, 1978;Bråthen & Oksanen, 2001;Olofsson et al, 2001;Moen et al, 2003). In the context of protecting rare vascular plants, the impacts of summer grazing are focal, since our arctic-alpine rarities are found in the mountain chain, which is primarily used for summer grazing.…”

“…Highest diversity is found under intermediate grazing conditions, e.g. on fairly intensely used winter ranges, characterized by a species-rich mixture of fruticose lichens, cup lichens, crustose lichens and bryophytes (Du Rietz, 1925;Dahl, 1957;Helle & Aspi, 1983;Oksanen, 1978;Oksanen & Virtanen, 1995;Olofsson et al, 2001;Väre et al, 1995;Suominen et al, 1999a).…”

“…Studies on the impact of reindeer on Fennoscandian arctic-alpine nature have improved our knowledge on the impact of reindeer on the coverage of lichens (Johansen et al, 1995;Ihse & Allard, 1995;Johansen & Karlsen, 1996;Allard et al, 1998), on nutrient mineralization rate and primary production (Stark et al, 2000;Olofsson et al, 2001;Stark & Grellmann, 2002), on ground temperatures (Olofsson et al, 2003) and on abundances of ground-dwelling (Suominen et al, 1999a;Suominen et al, 1999b) and galling (Olofsson & Strengbom, 2000;Herder et al, 2004) invertebrates. Vegetation studies have corroborated the predictions of IDH in the context of lichen rich heathlands, which become overwhelmingly dominated by Cladina stellaris in the absence of reindeer, whereas only crustose lichens survive on the most grazed and trampled sites along reindeer fences.…”

Use and abuse of reindeer range

“…Hill et al 1992, Manseau et al 1996, and the duration of the present experiment was short. In plant communities such as those studied here, where reindeer have grazed since the latest ice age, the species compositions and local species pools are determined by their grazers (Zimov et al 1995, Mulder 1999, Olofsson et al 2001, see also Jefferies et al 1994.…”

“…Moen et al 1993, Olofsson et al 2001. Crawley (1997) states that the ability of grasses to withstand grazing is their most famous trait.…”