EARLY SERAL COMMUNITIES IN A LIMESTONE QUARRY - AN EXPERIMENTAL-STUDY OF TREATMENT EFFECTS ON COVER AND RICHNESS OF VEGETATION

A study was made of the factors thought to be responsible for slow development of vegetation on a limestone quarry floor, and on the interdependence of cover and species richness. Three were chosen for special attention: low seed input, low levels of plant nutrients, rabbit grazing. A factorial experiment was done on a very sparsely vegetated area to examine the separate and combined effects of sowing 2 widespread but locally absent species (Brachypodium sylvaticum and Lotus corniculatus), adding fertilizers, covering plots with cages to keep out rabbits. Measurements were made on percent cover, species richness, rooted frequency and flowering over 4 years. Plant cover increased by up to 7 times that of controls when 1 or 2 factors were applied, and by 15 times when all 3 were applied simultaneously, reaching 78% cover in 1984. The number of species recorded in the whole experimental area rose from 46 in 1980 to 65 in 1984. The mean number per plot rose from 22 to 32 m-2 but there was no significant difference between treatments in 1983 or 1984. Flowering was enhanced by several of the treatments by cages, in 1984. Rooted frequency (all species combined) was at first increased significantly by the sowing treatments but by 1984 was greatest in the cage + fertilizer treatments. Ideally one may wish to encourage maximum cover and diversity in accelerating the development of vegetation in a quarry. However, these two goals appeared to be incompatible, at least in the short term. For reasonably high values of both variables (cover and combined rooted frequency), a good strategy was to combine sowing with either cages or fertilizer but not both.