EFFECTS OF SMALL-SCALE ANIMAL DISTURBANCES ON PLANT ASSEMBLAGES OF SET-ASIDE LAND IN CENTRAL GERMANY

The distribution, density acid cover of small-scale natural disturbanc es was surveyed in semi-natural and set-aside vegetation in a hilly la ndscape in Central Germany in the spring of 1995. More of the landscap e was disturbed on set-aside agricultural land in valleys (1.02 %) and on warm south-facing slopes (1.33 %) than on rocky hilltops (0.3 %) a nd cool north-facing slopes (0.56 %). The major agents of disturbance on set-aside fields were moles, rodents (and their predators) and wild boars. In surrounding semi-natural grasslands, rabbit warrens were co mmon on south-facing slopes and mound-building ants on north-facing sl opes. Disturbances were significantly clustered and frequently superim posed. In order to investigate the effects of disturbance quality on p lant assemblages in set-aside fields, two common types of disturbances were compared. These were grazing lawns (0.4 - 1.0 m(2)) maintained t hroughout the summer by common voles (Microtus arvalis), and excavatio ns, 0.7 - 1.6 m(2) in area, where wild boars (Sus scrofa) grubbing for food had removed vegetation and top soil in early spring. Both types of disturbances increased plant species richness on the local scale. W ind-dispersed annual and pauciennial forbs of ruderal habitats (e.g. C arduus acanthoides, Cirsium vulgare, Matricaria maritima, Senecio vern alis) were most abundant on the superficial disturbances made by voles , whereas small, ephemeral field weeds (e.g. Polygonum aviculare, Anag allis arvensis, Chenopodium album, Fallopia convolvulus) predominated on patches grubbed by boars. This study confirms that small-scale dist urbances by animals provide a variety of regeneration niches for field weeds and ruderals. The rate of decline in plant species richness on set-aside land is likely to be reduced where land is utilized by a var iety of herbivorous and soil-moving mammals.