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 century-old 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.