Reindeer grazing reduces seed and propagule bank in the High Arctic

It is commonly assumed that plant establishment in the High Arctic is limited by severe abiotic conditions by a paucity of popagules and seeds. Heavy reindeer grazing may reduce plant allocation to reproduction and removes significant proportions of flowers and seeds, thus reducing contributions to seed bank. In contrast, foraging and trampling may break up existing mature plants, increasing the vegetative propagules in the soil. To determine the effect of grazing on colonization potential in the High Arctic, two studies were carried out: (i) a comparison of seed bank inside and outside three long-term reindeer (Rangifer tarandus platyrhnchus (Vrolic)) exclosures and (ii) an investigation of the germinable seed and propagule bank of two neighbouring peninsulas with contrasting reindeer grazing history in north-western Svalbard (79 degrees N, 12 degrees E). Seed banks inside reindeer exclosures germinated significantly more seedings (596 seedlings . m(-2)) than those outside (263 seedlings.m(-2)). Species composition and total plant cover was similar on both peninsulas, but forage-plant cover was lower on the heavily grazed peninsula (Broggerhalvoya) than on the adjacent lightly grazed peninsula (Sarsoyra). Broggerhalvoya had significantly lower species richness and density of seed and propagule bank (0.21 +/- 0.02 germinating species per sample, 0.15 +/- 0.02 propagule species per sample, 416 +/- 103 seedlings.m(-2), 283 +/- 78 propagules.m(-2)) than did Sarsoyra (0.44 +/- 0.40 germinating species per sample, 0.35 +/- 0.03 propagule species per sample, 1016 +/- 188 seedlings.m(-2), 782 +/- 238 propagules.m(-2)). These results imply that reindeer depleted both the seed and propagule banks, thus reducing the potential for colonization of disturbed areas. Grazing may, therefore, have a lasting impact on High Arctic communities.