This paper describes early secondary succession on an old field on limestone released from cultivation four years previously. Seasonal changes in plant composition after spring grazing by sheep are compared with those in ungrazed controls. Grazed and ungrazed paddocks were laid out in Latin squares. Plants were sampled before and several times after grazing in April, at several spatial scales.
Major changes in plant abundance and sward characters such as height and density persisted throughout the growing season. Annual herbs increased after grazing, but annual grasses declined, as did short-lived perennial herbs. Effects on perennial herbs were weak; perennial grasses usually increased but this depended on the species. This pattern confirms that sheep grazing affects the direction, as well as the rate of succession. Some effects, such as increases in biennial herbs and in species richness, were only evident at large scales of sampling, suggesting that they arose from changes in rare and widely dispersed species. Other species were affected at different spatial scales, and no one sampling method detected the full range of effects.
These results indicate the potential power of manipulating grazing early in secondary succession for directing the course of community change, for conservation or other purposes. * Nomenclature follows Clapham et al. (1962) ** This study is funded by a grant from the Nuffield Foundation to V.K.B. We thank the Wytham Management Committee, Oxford University, for permission to use the site, and the staff of the University Farm, especially Richard Bampton and Cheryl Howes, for making the grazing possible. Alan Gange, Nicola Marples, Fiona Matthews, Bridget Peace, Anne Storr and others helped at various times with field recording.