Question: How do reduced levels of summer grazing by reindeer affect the abundance, composition and species richness of mountain plant communities?
Location: Arctic-alpine mountain vegetation 700–850 m a.s.l., Saana Conservation Area, northwestern Finnish Lapland.
Methods: Permanent plots were established in 1990 and resampled in 1999 or 2001. The number of reindeer had considerably declined from the 1980s to the 1990s and we followed the recovery of vegetation. The comparisons between 1990 and 1999/2001 were made at seven sites differing in their original grazing pressure.
Results: At the initially heavily grazed sites, lichen abundances increased, but at the lightly grazed sites the abundances of lichens decreased. Graminoids declined at all sites, but the change seemed to be greatest at the most heavily grazed sites. Forbs increased slightly across all sites. At the species level, lichens and graminoids responded most notably to the reduction of grazing pressure. Individual species responses in shrubs were variable and among forbs, typical species of species-rich Dryas heaths increased. Total species richness increased at all sites and the change was greater at heavily grazed sites. This increase resulted mainly from increased bryophyte and lichen species richness but also from a slight increase in vascular plant species richness.
Conclusions: These results suggest that lichens are the group most responsive to the reduction of heavy summer grazing by reindeer and that lichens and forbs typical in arctic-alpine Dryas heaths are favoured over graminoids under reduced grazing. Heavy grazing decreases overall species richness with the most pronounced effects on bryophyte and lichen species richness. The results support the hypothesis that heavy summer grazing may shift the composition of mountain plant communities towards that of grasslands and show how this shift may be reversed under reduced grazing.