Large-scale grazing history effects on Arctic-alpine germinable seed banks

Grazing constitutes a selective pressure on vegetation recruitment through modification of the seed banks. Here we address changes in seed bank density and its life history trait composition in centuryold pastures, where contrasting reindeer densities have developed during the last decades. We cover the actual scales used by these wide-roaming herbivores by sampling 70 productive tundra habitats over 7,421 km2 in the reindeer summer pastures of Northern Norway. Results showed that the seed bank density was significantly lowered where reindeer densities had increased in recent decades, whereas the century-long history of grazing probably explains the main seed bank traits typical of grazing tolerant plants. The dominant trait characteristics were small seeds (\\0.5 mg), seeds lacking dispersal mechanism and individuals with a graminoid growth form. Finally, differences between regions introduced trait variation independent of grazing history, reinforcing the importance of using scales covering several contexts when designing ecological studies.