Reindeer grazing history effects on plant recruitment and life history traits from the germinable seed bank

Abstract

Seed banks represent a source from which new vegetation may quickly arise if the existing stand is disturbed. It is increasingly discussed that reindeer grazing modifies the seed banks in northern ecosystems. However no large-scale studies have been carried out to support this hypothesis. Because reindeer could constitute a selective pressure on vegetation recruitment, the present study investigated seed banks in terms of plant life history traits (i.e. life form, growth form, diaspore morphology, and seed weight) in paired areas with a similar long term history of grazing but contrasting reindeer densities during the last 20 years in Finnmark (Norway). In this study, 63 species geminated from the seed banks, while seed bank densities varied from 575 to 3 506 seeds m2 per area independent of reindeer density. Reindeer density did not affect the presence of any plant life history trait in the seed banks, with graminoids, hemicryptophytes, and small (0-0.5 mg) and unappendaged seeds being the most abundant traits under both density regimes. Moss layer thickness was negatively correlated with the seed bank density, indicating it could constitute a mechanical barrier for the input of seeds to the seed bank. The results from this study do not show an effect of a short term increase in reindeer densities, whereas they are consistent with a seed bank trait composition expected from vegetation with a long term grazing history.