The effect of the abandonment of grazing on the mosaic of vegetation patches in a temperate grassland area in Hungary

Abstract

Five-year and almost 20-year effects of the abandonment of a former pasture were investigated based on the comparison of three vegetation maps (1983, 1988, 2002) as a first step in a future hierarchical evaluation of the complex effects of this land use change on the vegetation. The grassland studied has been being composed of several stands (patches) of close-to-natural and degraded communities (vegetation types). Vegetation types were defined on the basis of their species composition and abundance pattern in 1983 and were supervised with the same methodology in 2002. The fact that the original vegetation types continued to exist, allowed the comparison of the three vegetation maps. The relative cover of the vegetation types was compared in the three periods. The comparison revealed drastic changes, especially between 1988 and 2002. On the basis of the vegetation maps transition matrices were produced, which described changes between the three points of time in a pairwise manner. The transition matrix describing changes in the first 5 years mainly contained self-replacements, while the matrix corresponding to the next 14 years and the one describing the changes during the whole studied period contained strongly directional transitions, where sources and sinks were identifiable. The transition matrix between 1983 and 1988 was cubed in order to produce a matrix corresponding to 15 years of vegetation development. The cubed matrix was compared with the transition matrix of 1988 and 2002 and was found to be different, which pointed to a lag period before the effects of the removal of grazing became observable. The directionality of transitions and the expected future dynamics were estimated by multiplying the cover distribution of vegetation types in 2002 with the 20-year transition matrix. This “prediction” revealed the differences in the directionality of transitions between pairs of vegetation types and provided a null expectation for the future exploration of the complex traits of these dynamics.