What are the long-term effects of livestock grazing in steppic sandy grassland with high conservation value? Results from a 12-year field study

To examine the necessity of livestock grazing for managing threatened sand vegetation so as to ensure and develop its nature-conservation value, we investigated a grazing system in a model nature reserve (German upper Rhine valley) characterized by threatened steppic sandy grassland (Allio-Stipetum vegetation complex: Habitats Directive Annex I, priority type 6240, additionally Koelerion glaucae: priority type 6120). The area has been grazed by sheep and additionally by donkeys since late summer of the year 2000. We established ungrazed (Au) and grazed plots (Ag) in the Allio-Stipetum complex in a systematic grid-plot design before grazing impact started. We sampled phytosociological releves yearly in the Au/Ag plots for 12 vegetation periods. Additionally, we sampled releves on former farmland adjacent to the Allio-Stipetum complex (systematic grid-plot design) over ten vegetation periods. These former fields (Fg) were integrated in the grazing system since the beginning of the study. A constancy table was produced for Au, Ag, Fg. To determine the portions of target species (Koelerio-Corynephoretea, Festuco-Brometea species) we calculated target-species ratios (proportion of target species in comparison with the total species number; qualitative or quantitative approach: TSRqual/quant ). We tested the effects of grazing, year and interactions on structural and phytodiversity characteristics of the releves by mixed linear models. The results of the long-term experiment confirmed significant beneficial effects of grazing on habitat-typical structure and phytodiversity: e. g. reduction of litter, support of species which are short in height ( 50 cm), support of the diversity of all plant species, of non-graminoid herbs and of target plant species, reduction of Calamagrostis epigejos, positive effects on TSRqual and TSRquant values. Similar developments, e.g. for phytodiversity and Calamagrostis epigejos cover, were observed on the former fields, but there are still seed limitations and high ruderal-plant dominances. In general TSRqual/quant show remarkable increases, but do not reach the values of the Ag plots. Concerning aims of nature conservation, the habitat-typical vegetation structure and phytodiversity of the Allio-Stipentum shows an excellent development as a consequence of the used grazing management. However, occasionally small populations of target species did not increase (e.g. Koeleria glauca). The former fields show a development towards valuable sandy grassland