The importance of spring and autumn grazing for seedling establishment in semi-natural grasslands

摘要

The diversity of available regeneration niches is generally considered a key factor for plant species diversity in semi-natural grasslands. The traditional management of hay meadows in Scandinavia included grazing in autumn and occasionally also in spring. In this study, I used a seeding experiment to examine the effects of spring and autumn grazing on seedling establishment in Conopodium majus, Pimpinella saxijraga, and Knautia arvensis in a hay meadow with traditional management. The experiment included four different combinations of autumn and spring grazing and three levels of disturbance in the bottom layer in a factorial design. The effects of grazing were highly species-specific and seasonally dependent. Autumn grazing had a clear positive effect on seedling establishment in Pimpinella. The results suggest that both removal of regrowth in the field layer and an increased frequency of gaps in the bottom layer (dominated by bryophy tes) contributed to the positive effect of autumn grazing. Infact, no Pimpinella seedlings were present in plots without grazing or disturbance. In Conopodium, spring grazing alone or combined with autumn grazing resulted in the highest plant establishment at the end of the experiment one year after germination. In contrast to the other species, Knautia responded weakly to grazing. The results demonstrate that grazing in spring and autumn can have positive effects on seedling establishment in hay meadows and should therefore be considered as part of the management strategy in species-rich hay meadows.