Effects of large wild boar disturbances on alpine soil seed banks

Abstract

Wild boar rooting is considered one of the main large soil disturbances affecting the structure and composition of plant communities in alpine grasslands. While direct consequences on plant community have been widely studied, their effects on soil seed banks have received little attention although rooting is assumed to determine the successional processes and ultimately the ecological recovery of the communities. The aim of this study is to assess the effect of wild boar rooting on species and community soil seed banks. The rooting effect was studied in terms of seed abundance and diversity in the most disturbed plant communities by wild boar in Pyrenean alpine grasslands. Two hundred soil core samples were collected at two depths to account for (short/long term) persistent and transient seed banks within and outside wild boar rooting in those grasslands. The ‘seedling emergence method’ was used to identify and quantify seeds from the germinable seed bank. The soil seed bank found within disturbances was smaller than expected. At the species level, the main type of seed bank represented in these grasslands was long-term persistent, comprising 75% of the seeds found. Rooting turned long-term persistent seed bank into short-term persistent and transient, by exposing seeds from the deepest part of the soil to germination conditions at the surface of disturbed areas. At the community level we found that rooting homogenized soil seed banks by increasing seed abundance and species richness in species-poor communities, while decreasing seed species dominance in nitrophilous communities. These results suggest a deep alteration of the structure of seed banks by wild boar rooting, which in turn, may not represent a real chance for colonization from soil seed banks.