Significance of ant and rabbit disturbances for seedling establishment in dry acidic grasslands dominated by Corynephorus canescens

Abstract

Seedling establishment is a crucial bottleneck for vegetation dynamics. However, little is known about the spatio-temporal patterns of small-scale disturbances offering bare substrate for germination, nor about the establishment rates of key pioneer species. This paper presents (i) temporal patterns of ant and rabbit disturbances in dry acidic grasslands dominated by Corynephorus canescens on inland sand dunes, and (ii) establishment rates of Corynephorus canescens, Spergula morisonii, Teesdalia nudicaulis and Rumex acetosella on disturbance patches versus undisturbed controls. Spatially explicit disturbance patterns of five sites - characterized by the associations Spergulo in morisonii-Corynephoretum typicum and Spergulo morisonii-Corynephoretum cladonietosum - are recorded throughout 17 months at two scales (1 m x 1 m; 0.1 m x 0.1 m) in addition to plant establishment rates and cryptogam cover. A total of 1050 data records from 75 permanent plots is statistically analysed. Between 1% and 15% of the grasslands are covered by disturbance patches with a distinct seasonal pattern and limited longevity. For Corynephorus canescens, Spergula morisonii and Teesdalia nudicaulis, successful seedling establishment is significantly higher on small disturbed plots than on control plots, which are covered by cryptogams. Hence, these results provide evidence of the importance of small-scale disturbances as a window of opportunity for seedling establishment in dry acidic grassland. The findings are discussed with regard to the contribution of disturbance to the balance of grassland dynamics.