The role of gap dynamics for the regeneration of the natural spruce forests in the Harz Mountains

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In Central Europe only few places are known where vegetation regeneration after natural disturbances can be studied in natural or near-natural Picea abies forests; one example are the slopes of Mt. Brocken. Although being mono-dominant, the spruce forests at Mt. Brocken are unique because they contain autochthonous Picea abies genotypes. In addition, the herb layer is comparably species-poor with a high proportion of clonally reproducing species. Based on the assumption that gap dynamics are equally important for regeneration of the tree and herb layer as in other forest types, the project seeks to test four main hypotheses. For the tree layer, it will be tested whether gaps promote the establishment of allochthonous genotypes of Picea abies and whether the proportion of autochthonous genotypes increases with gap age due to strong environmental selection. For herb layer regeneration the hypotheses are tested that generative reproduction is enhanced in gaps for the abundant clonal species Vaccinium myrtillus, Calamagrostis villosa and Trientalis europaeus and that clone size increases with gap age. To attain its goal the project employs GIS, dendrochronology and molecular genetic approaches. Using aerial photographs, gaps will be stratified according to age and sampled for species composition and population structure of target species. The field observations will be supplemented by experiments on establishment, frost hardiness and vegetative regeneration capacity of spruce as well as on clonal growth of target herbs.