Succession of disturbed and undisturbed chalk grassland at Aston Rowant National Nature Reserve: dynamics of species changes.
The first 14 years of secondary succession, from 1969 to 1982, are described in a randomized block design experiment on chalk grassland at Aston Rowant, UK. There were 4 blocks with 4 treatments: annual grazing by sheep, no treatment, and ungrazed after disturbance by burning or rotary tillage in 1969. Total numbers of species in 10 × 12 m plots and 1 m2 quadrats were variable, with few clear trends. Differences in species packing accounted for the highest numbers being recorded in the quadrats but not in the plots of the grazed treatment. Depletion curves over 14 years for the initial species complement in the quadrats were least in the grazed grassland, and greatest in the untreated and rotary tilled. Burnt plots were intermediate. Annual turnover of species in the quadrats was greater in grazed grassland than in the successional treatments as a result of the mortality and recolonization from the grazing level which maintained this plagioclimax grassland. Successional grassland was influenced more by competitive interactions between species. Constant and transient species in the quadrats of each treatment are given. Numbers of species annually colonizing and lost from the quadrats tended to fluctuate in a similar way on the different treatments. This was probably due to weather, as the 1976 drought apparently affected the quadrat results on almost all the plots.