Pattern of succession in old-field vegetation at a regional scale.

In contrast to the many detailed studies on succession conducted at local scales, there is still a lack of studies on succession at broad geographical scales. In this paper the following questions are addressed: Which of the components of seral old-field vegetation are associated with environmental factors at a broad geographical scale? To what extent do target (typical of natural and semi-natural vegetation), non-target (alien and synanthropic) and endangered species participate in the succession and on which factors is their participation dependent? Altogether 282 phytosociological relevés were recorded in old fields located in various parts of the country. The fields were from 1 to 91 years old. The following environmental characteristics were determined for each old field: altitude, phytogeographic region, soil moisture (dry,mesic, wet) and bedrock (basic, acidic). Species were classified based on the extent to which they are endangered, origin (natives, archaeophytes, neophytes) and affiliation with vegetation units. Vegetation data were analysed using multivariate statistics, generalized linear mixed models and regression trees. The results indicate that all the environmental characteristics had at least a slightly significant effect on the species composition of the different seral stages. Succession clearly differed in the three subseres and depended on soil moisture. The number of target species typical of deciduous woodland, dry grasslands and fringe communities increased during succession. In contrast, the number of archaeophytes, neophytes and synanthropic species decreased with field age. More endangered and target species and fewer archaeophytes, neophytes and synanthropic species occurred in warmer lowland than in colder upland areas. The number of endangered, target and the total number of species decreased with soil moisture, while the number of neophytes and synanthropic species increased. The number of target species typical of dry grasslands decreased with altitude while that of synanthropic species increased. The age of old fields and soil moisture appeared to be the most important drivers of succession at a broad geographical scale. In addition to local site factors, climate represented by altitude and reflected also in biogeographical regions modified the course of succession. Succession was clearly divergent.