The Effect of Excluding Rabbits from Grassland a (Xerobrometum) in Breckland, 1936-60

Abstract

Comparison between ungrazed and intermittently grazed grassland on a shallow, highly calcareous soil is based primarily on numerical data obtained annually from 1936 to 1960. In the ungrazed pasture there is an increase in the number of species and the additions strengthen the floristic affinities of grassland A with the Xerobrometum of the continent. The significance of rabbit grazing in causing floristic poverty and geographical localization of species is emphasized. The populations of some species are not directly affected by grazing. Palatable species, released from grazing, increase and show a periodicity in numbers related to (a) the periodicity of a series of wet springs and (b) the cyclic behaviour of a highly competitive, even-aged population of Hieracium pilosella, itself established by seed under similar conditions. For a time it replaces the dominant Festuca ovina, but on its decline, Festuca increases. Equilibrium between Festuca and Hieracium has not been reached before the new entrant Zerna erecta presents, in the continued absence of rabbits, a more likely permanent challenge to Festuca.