The effect and extent of heavy grazing by reindeer in oligotrophic pine heaths in northeastern Fennoscandia

Thirty and fifty years old exclosures established in northeastern Fennoscandia in lichen-rich oligotrophic pine Pinus sylvestris forests on podzolised soil were used to study the effect of reindeer grazing on pine fine roots, microbial activity, and on bryophyte, dwarf shrub and lichen biomasses. There were significantly less lichens, especially Cladina stellaris, at grazed than at ungrazed sites. Coverage of other lichens like C. arbuscula and C. rangiferina and bryophytes, especially Dicranum spp., benefitted from grazing. The biomass of vascular plants, mainly Calluna vulgaris, Empetrum nigrum and Vaccinium vitis-idaea, was reduced at grazed sites, although their coverage was not influenced. Microbial activity was significantly lower at grazed sites. The influence of grazing is most obviously mediated by reduced soil moisture during dry periods at grazed sites. Fine root parameters (per soil and stem volumes) were lower at grazed sites (pPCA = 0.072), the first principal component consisting of a number of fine root tips, length and weight. Grazing decreased all exchangeable nutrients by 30-60% in organic layer. Based on PCA the decrease was significant for exchangeable nutrients, although of individual elements only P and S showed statistically significant difference. The extent of heavy grazing in northeastern Fennoscandia coniferous forest was revealed by remote sensing. It revealed extensive area in which reindeer lichens are reduced in northeastern Finland. The Finnish-Russian border can be clearly distinguished in the satellite image composite.