Changes in the composition of sand grasslands along a climatic gradient inHungary and implications for climate change

The primary objectives of this study were (1) to document the changes in th e composition and structure of a semiarid grassland (Festucetum vaginatae) along a climatic gradient in Hungary, and (2), by applying the concept of " Space for Time Substitution", to form hypotheses on the possible effects of a predicted climate change on these grasslands. Three sites were selected along a 200 km transect in the sand forest-steppe vegetation of the Hungarian Plain. Percentage canopy cover was estimated b y species in 30 pairs of randomly located 16 m(2) quadrats at each site. Sp ecies were classified based on their phytosociological character, geographi c distribution, and Raunkiaer life form. We found that species richness, canopy cover, diversity, and the relative i mportance of dry grassland generalists, forest species, and Hemicryptophyte s decreased, whereas the relative importance of sand grassland specialists, Therophytes, and species with Continental and Sub-Mediterranean distributi on increased with increasing aridity. We;Found that the existing difference s in climate along the gradient are comparable to the predicted climate cha nge for the region, therefore, the changes observed along the gradient may serve as hypotheses on the possible future changes in grassland structure a nd composition. However, the rate of changes is unpredictable. The indirect effects of climate, such as higher forest cover and soil organic matter co ntent :it the wet end of the transect, may be important in driving the pres ent differences in grassland composition, and may buffer or considerably sl ow down the expected changes.