Study of Vegetation Change at Lakenheath Warren: A Re-Examination of A. S. Watt's Theories of Bracken Dynamics in Relation to Succession and Vegetation Management

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Abstract
(1) This paper documents the changes in (a) the distribution of bracken (Pteridium aquilinum (L.) Kuhn) and Scots pine (Pinus sylvestris L.) at Lakenheath Warren using a historical series of vegetation maps produced from aerial photography, and (b) the vegetation of A. S. Watt''s bracken v. Calluna (Calluna vulgaris (L.) Hull) plot. (2) The size of the bracken patch at Lakenheath Warren has increased by only 24 ha (< 0.2% per year) between 1918-22 and 1984, although ebbs and flows were found around the boundary. Since 1968 however, the centre of the bracken patch has degenerated from dense bracken to a sparse bracken/grass heath community. (3) There has also been a rapid invasion of the Warren by Scots pine, and no evidence was found to suggest that dense bracken inhibited invasion at this site. (4) At the "bracken v. Calluna area" the apparent stability reported by Watt, where there was interdigitation between bracken and the four phases of Calluna, has broken down. The Calluna has now almost disappeared, and bracken now covers most of the former Calluna area. (5) The results of this study were used to test some of Watt''s hypotheses on bracken dynamics and the relationship between bracken and other species. (6) The relevance of these results for the practical management of vegetation was also discussed, namely (a) the potential interference of bracken degeneration when making reliable estimates of both bracken encroachment and long-term sustainable yield, and (b) the management required to maintain both Calluna and bracken along an invading bracken front.

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