ABSTRACT
Vera's theory proposes that intense browsing pressure exerted by populations of large herbivores has historically had a major influence on the composition and structure of wooded vegetation in Europe. In addition, according to Vera (2000), high herbivore pressure leads to cyclical vegetation dynamics, in which tree regeneration is dependent on facilitation by spiny shrubs. Although the theory has had a significant impact on environmental policy and management, it has not been adequately tested. Here we present data from three field surveys undertaken in the New Forest, southern England, which examine tree regeneration in 1) woodland, 2) shrubland and 3) heathland. The implications of herbivory for woodland dynamics are also explored using a spatially explicit modelling approach. Results indicate that as hypothesised by Vera (2000), facilitation can be observed on woodland peripheries. However, tree regeneration was also widely observed in woodland and in heathland, where it is not necessarily dependent on the presence of spiny shrubs. Model outputs projected woodland expansion even in the presence of high herbivore pressure and without facilitation, a finding that is consistent with field observations at this site. These results highlight the need to identify with greater precision the situations under which Vera's theory is most likely to apply, and suggest the need for caution in using the theory to inform conservation management.
