Buchenwald-Sukzession nach Windwurf auf Zechstein-Standorten des südwestlichen Harzvorlandes

Abstract

Kompa, T.; Schmidt, W.: Plant succession in windthrown beech (Fagus sylvatica) forests on gypsum karst and dolomitic limestone in the Harz Mountain foothills of southern Lower Saxony, Germany. – Hercynia N.F. 38 (2005): 233–261.Following a local summer storm in 1997, plant succession in windthrown beech forest stands (Carici- Fagetum, Hordelymo-Fagetum) on base-rich Zechstein soils (gypsum karst, dolomitic limestone) in the foothills of the Harz Mountains (southern Lower Saxony) were studied on permanent plots from 1998 through 2001. Vegetation development during natural reforestation of these unmanaged stands is discussed relative to intensity of initial disturbance on shallow vs. deep soils (compared are unthrown stands, gaps and extensively thrown stands). The species diversity increased throughout the first three years, but then declined. The natural regeneration was everywhere dominated by young climax tree species (first of all Fraxinus excelsior, Fagus sylvatica, Acer pseudoplatanus) while pioneer trees hardly occur. The population density of natural regeneration was very high and doesn´t show a distinct dependence on the severity of disturbance. After four years of succession, all stands except those extensively thrown on shallow gypsum karst are characterised by the dominance of species of the former forest floor vegetation. In gaps - on deep soils also under conditions of large-scale windthrow - these forest stands keep an astonishing floristic similarity compared to the parent state. The analyzed development of functional species groups (quantitative spectra) confirms this successional patch by constant percentual shares of such groups that are typical for Querco-Fagetea communities. Extensively thrown stands on shallow gypsum karst (mostly Carici-Fagetum) showed another successional pathway. Here, pioneer vegetation increased rapidly and became partly dominant. Typical species groups of these stands are e.g. Epilobietea, Artemisietea, pioneer shrubs, endozoochor dispersed species, species with long time persistent seed bank (>5 years) and light indicating species. But even here the forest floor species perennate under the pioneer vegetation and keep constant or partly increasing absolute coverages. The typical Querco-Fageta species are nowhere outcompeted. So, these base-rich beech stands show a very resilient response to natural disturbance. A comparison with other windthrown beech stands in the Harz Mountain foothills shows a site-dependent gradient of natural regeneration. The more base-rich the substrate, the more independently from severe extrorse disturbance natural reforestation proceeds. 1. Base-rich, deep soils (e.g. Hordelymo-Fagetum): forest floor species and natural regeneration of the climax trees dominate independently from the severity of disturbance. 2. Base-rich, shallow soils (e.g. Carici-Fagetum): gaps regenerate very rapidly and don´t change significantly, extensively thrown stands regenerate more slowly and are covered by increasing pioneer vegetation. 3. Acidic soils (e.g. Galio odorati-, Luzulo-Fagetum): regeneration depends strongly on the severity of disturbance, the more the stand is disturbed, the more slowly the regeneration proceeds and pioneer vegetation becomes dominant. A complete species-change as it is postulated in the mosaic cycle-concept (Remmert 1985, 1987, 1991) can´t be confirmed for Central European beech forests which are in their optimal phase. Succession in these forest communities doesn´t involve major species changes but rather temporal changes of dominance of residual species.