Loss of semi-natural grasslands in the Hungarian forest-steppe zone in the last fifteen years: causes and fragmentation patterns

摘要

Most of the semi-natural grassland areas in the forest-steppe zone of the Great Hungarian Plain disappeared by the end of the 19th century. However, the destruction of these remnants continued into the 20th century and has further accelerated since the political changes of 1989. In this study we examined the relationship between the fragmentation characteristics of the semi-natural grassland patches and their exposure to anthropogenic destruction based on the example of a characteristic region of theGreat Hungarian Plain, the Danube-Tisza Interfluve ("Duna-Tisza koze")- To detect losses, we used 1:25,000 topographic maps of the Hungarian Army (made at the end of the 1970s) to locate the semi-natural grassland fragments at that time, and compared these to the results of a project, which mapped all the remaining semi-natural grassland areas of the region between 1996-2000. To describe the fragmentation characteristics of the grasslands we used four landscape indices (patch area, perimeter-area ratio, fractal dimension and proximity index), which describe simple geometrical features of the patches (size, shape, isolation). We also differentiated four main destruction types (ploughing, construction, afforestation and miscellaneous). Altogether, we found that 15% of the grasslands fragments have disappeared over the 20 year period with ploughing and afforestation being the main destruction types. The most threatened patches were the small and isolated fragments. Indices for patch area and proximity were found to be the most informative describing the fate of the patches.