The impact of deer on woodlands: the effects of browsing and seed dispersal on vegetation structure and composition

The effect of deer on woodland vegetation is reviewed, focusing on processes that are likely to bring about changes in structure and composition. By browsing on tree seedlings, shrubs and climbers, deer tend to reduce stem densities, limit height growth and reduce foliage density, creating a more open understorey. Light penetration to the ground can be increased, providing more plant cover close to the ground surface. Using results from 13 studies in temperate woodlands, the effects of deer browsing on the species richness and diversity of trees were analysed using general linear models. The results show that deer tend to reduce the diversity of seedlings, and that the effect is greater at higher deer densities. Differences in susceptibility of tree species were evident, with some species being depleted by deer at all sites, whereas others declined in some sites but increased in others. The effects of deer on the amount and composition of regeneration appear to depend on site characteristics, including the light regime and composition of the ground vegetation. Although few studies of seed dispersal by ungulates (endozoochory) have been made in Britain, deer have been shown to be effective seed dispersers of a number of plant species. Plants with small hard seeds are most likely to survive digestion. Most of the species known to be dispersed in this way include grasses and small herbs. In view of the fact that dispersal mechanisms of many woodland species are not well understood, endozoochory may be more important than is generally realized.