A community and population perspective of the possible role of grazing in determining the ground flora of ancient woodlands

Ar. Watkinson et al., A community and population perspective of the possible role of grazing in determining the ground flora of ancient woodlands, FORESTRY, 74(3), 2001, pp. 231-239
Citations number
Categorie Soggetti
Plant Sciences
Journal title
ISSN journal
0015-752X → ACNP
Year of publication
231 - 239
SICI code
The ground flora in ancient woodlands is affected by a wide range of factor s at a range of scales. In an analysis of 495 sites of ancient woodland thr oughout Great Britain, regional trends in ground flora species composition were explained primarily by climatic and soil variables, while the most imp ortant variable determining species richness was soil pH. In this analysis, similar to 85 per cent of the variation in ground flora composition could not be accounted for and was probably a result of local variation in a rang e of ecological processes including grazing by vertebrates. Within sites, t he use of exclosures indicates that large herbivores may have a dramatic im pact on vegetation structure and composition, but it is a very crude tool. The exclosures are often too small, and measurements do not allow for varia tions in the density or seasonality of grazing and ignore the fact that pla nt responses are typically non-linear. Manipulation of grazing levels is cr itical if we are to understand the impact of grazing on vegetation structur e and composition. Individual species vary in their responses to grazing. A population approach is used to illustrate how it is possible to explore ho w individual species respond to grazing. This is illustrated with reference to Anemone nemorosa and how intermediate levels of grazing are expected to favour this species. Complex, and as yet poorly understood, feedback mecha nisms between the plant and the grazing animal will contribute to the spati al structuring of grazing impacts on the woodland ground flora. A major cha llenge for predicting the impact of grazing on plant populations and commun ities is the quantification of the spatial grazing pattern.