The Effect of Excluding Rabbits from Acidiphilous Grassland in Breckland

Abstract

(Watt 1957) combined a record of the change, with an explanation of the different results in terms of the different initial floristic potential and the duration of the experiment. The floristic changes in the enclosed area were interpreted as part of a pattern determined by stages in the life cycle of the dominant Festuca ovina. Data from acidiphilous grassland show corresponding changes which are presented only in the detail necessary as a background to the formulation of problems raised by the various patterns of behaviour shown by the different species (Watt 1960). The acidiphilous grassland (grassland F of Watt 1940) grows on heavily podsolized infertile sand. At the start of the experiment (1936) it was dominated by Cladonia silvatica agg. with Festuca ovina, Agrostis canina, A. tenuis; Lixzula cammpestris, Galium saxatile and a few other species forming a sparse population of individuals or patches. Intensive grazing continued until 1941 when the rabbit population was virtually exterminated. After the war a few rabbits returned but their numbers remained small until 1954 when they were wiped out by myxomatosis. No sheep have been grazed on the area. In 1941 tanks introduced a new factor. Crushed in dry weather by the tanks, the lichen fragments were blown away leaving bare soil: in wet weather the lichen was pressed into a slime which dried to a crust checking wind erosion. In the years of the war little erosion took place and Polytrichum piliferum and P. juniperinum initiated a widespread colonization and succession (Watt 1938) whose development to a pasture was expedited by the abundant seed production of the ungrazed Festuca ovina. Agrostis spp. too spread, but not so fast. The slight grazing of the post-war period has made little impression on a pasture in which Festuca ovina and Agrostis spp. are now the physiognomically dominant plants, accompanied by subseral stages with Polytrichum spp., Cornicularia aculeata and species of Cladonia. Deschampsiacflexuosa, present in one patch on the warren in 1936, now forms several colonies in the area of grassland F. Small areas of lichen-dominated vegetation escaped destruction by tanks. These happily included the permanent control plot, whose carpet of Cladonia remained intact, the nearest tank track running obliquely to it and 25 cm distant at its nearest point. The enclosure, established in 1936, was similar in area (6 m x 6 m) and construction, with four corner posts and wire netting (3.2 cm mesh), sunk 15 cm in the soil. As in grassland B a distinction must be made between the margin of the enclosure under the influence of the wire netting and the rest of the plot. At the