Vegetation history, recent dynamics and future prospects of a Hungarian sandy forest-steppe reserve: forest-grassland relations, tree species composition and size-class distribution

摘要

Pannonian forest-steppes host a high number of endemic species and contribute to landscape-scale heterogeneity. Alterations in the proportion of forests and grasslands due to changes in land-use practice and climatic parameters can have serious nature conservation consequences. Hypotheses about forest-steppe dynamics have rarely been verified by detailed analyses, especially for the sandy forest-steppes. We integrated historical analysis, aerial photo interpretation and field investigation to determine how vegetation of a sandy forest-steppe has changed, how current dynamical processes operate and how native and exotic tree species regenerate under present conditions. The vegetation of the study area before the onset of major anthropogenic environmental transformations in the Carpathian Basin may have been a mosaic of forested and unforested patches. However, there is strong evidence that after heavy deforestation, the region was almost completely treeless between the 15th and the 19th centuries. Forest cover was able to recover by the 1800s but the lack of forested areas in the region for centuries explains why forest patches are still poor in species. Grasslands, which existed continuously, are more diverse, supporting several rare and endemic species. From 1953 till 2013, 72.45% of the area proved to be stable, but 27.55% showed clear dynamical character, changing either from forest to grassland, or vice versa. Thus, cyclic dynamics can occur in sandy forest-steppes. We found that forest patches of different size, differently exposed edges and grasslands provide different habitats for the tree species. Exotic species were present in large numbers, probably due to the small size of the reserve and the lack of a buffer zone.