Long-term (1978-2003) effects of an extensive grazing regime on plant species composition of a heathland reserve

An extensive vegetation survey was carried out in 1978 in 'De Maten', one of Flanders' most diverse heathland reserves. As a consequence of this study, extensive grazing was introduced as a management regime. In 2003, all plots were again surveyed in order to examine whether vegetation composition and diversity have changed over this 25-year period, and hence to evaluate the long-term effects of extensive grazing on vegetation composition and diversity under the prevailing conditions of increased nitrogen deposition and acidification in Flanders. To gain a comprehensive insight into the changes in the plant communities, vegetation change was studied at three different hierarchical levels (community, plot and species level). Overall, heathland vegetation has little changed during the study period and the proposed management seems to have succeeded in preserving the characteristic heathland vegetation and in retaining its typical nutrient-poor, acid character. Our results indicate that an extensive grazing management, as commonly applied in many nature reserves, is able to conserve species diversity in heathlands subject to high levels of nitrogen deposition and acidification. However, a low grazing intensity is not able to fully prevent shrub and tree encroachment. Also, in the moist and wet heathlands, extensive grazing does not seem to be sufficient to prevent increasing grass dominance. Therefore, occasional additional mechanical management is needed.