Vegetation dynamics in european beech forests
Dynamic processes can be classified in terms of their time scale, their spatial scale, the elements observed, and the degree of human impact. Using these categories the regeneration of the tree layer, the regeneration of the herb layer as well as successional changes of supraregional importance (immissions, global change) are discussed. A virgin (mixed) European beech forest consists of a mosaic of sub-stands that can be typified by their structure and developmental stage (phase) of the tree
... ase) of the tree layer; in some phases the tree individuals of each sub-stand are rather even-aged. Natural cyclic regeneration of virgin (mixed) European beech forests mainly includes the tree species of the terminal phases, expecially the beech itself. Changes of tree species composition within the cycle are the exception; in European beech forests light-demanding pioneers seem to be restricted to rather small patches under natural conditions. In contrast, the sequence (1) felled-area flora, (2) pioneer shrub/pioneer forest and (3) terminal forest is a characteristic feature of managed deciduous forests as a consequence of soil disturbances. During the cyclic regeneration of the tree layer of European beech forests the floristic content of the ground layer vegetation does not change fundamentally. Regeneration of many of the ground layer species of beech forests via generative diaspores is more or less restricted to micro-disturbances. In contrast disturbance of the topsoil and creation of open habitats for the establishment of saplings in the absence of competition is taking place all over a clear-cutting area. European beech forests are subject to changes of floristic structure caused by immissions. Especially nitrogen, emitted over decades in large quantities, causes a successive change in floristics: species requiring high amounts of nitrogen are increasing in beech forests all over Europe. Most of them are rapidly and tall growing species, outcompeting the slower and smaller growing acid-indicators. Soil acidification, although taking place, is therefore often not reflected in changes in the vegetation cover. Up to now, syntaxonomic changes are usually restricted to the levels below the association. Additionally some proportion of (beech) forest stands are presently changing since the regeneration following the abandonment of degrading land use practices has not yet been completed. As a consequence of changing climatic conditions (CO 2-content, air temperature, precipitation, storms) it is expected that European beech forests will change in the future. However, details of the flori-stic structure of future beech forest communities can not be predicted. Nevertheless, according to present knowledge, beech forests will remain the most important natural forests in Europe during the next century.