Rabbit Grazing, Plant Competition and Seedling Recruitment in Acid Grassland

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Abstract
(1) Two experiments were done to determine the effects of grazing by rabbits on plant recruitment in mature grassland and on cultivated soil. The first was a factorial experiment, with and without rabbit fencing, and with and without soil cultivation, carried out between 1986 and 1989 in acid grassland with a long history of rabbit grazing. In the second, carried out between 1982 and 1985 in two contrasting arable fields, rabbits grazed crops of winter wheat, with fencing exclosures erected at different times and for different durations. (2) Rabbit grazing affected the stature and composition of the grassland throughout the year. Species that increased in cover in rabbit-grazed grassland included the grass Anthoxanthum odoratum and the forb Rumex acetosella. Species that decreased included the grasses Festuca rubra and Agrostis capillaris and the forbs Vicia sativa and Trifolium repens. There was negligible change in the total number of plant species with grazing. (3) The cultivated treatments showed that the seed bank under the acid grassland was extremely heterogeneous. (4) Eight of the twenty-three commonest ruderal species beneath acid grassland decreased in cover significantly (e.g. Capsella bursa-pastoris and Papaver dubium), and none increased significantly. In contrast, most of the ruderal species in the seed bank of nearby arable soils increased under grazing. (5) Most plants species on cultivated grassland soils regenerated from vegetative fragments (e.g. Holcus mollis, Stellaria graminea, Rumex acetosa and R. acetosella), rather than by germination of seed. Regrowth shoots outnumbered seedlings by a factor of between 1.3 and 23.3. (6) The extent of spatial heterogeneity within and between plots in both the composition of the buried seed bank, and in recruitment by vegetative regrowth, highlights the need for large sample size in this kind of study. (7) The mechanisms that determine whether a plant species increases or decreases under grazing are discussed.