Constancy and dynamics in a species-rich calcareous beech forest. Changes within a large transect 1981-2011

On the plateau of the Gottingen Forest, an area of 12 ha of a ca. 145-yr- old species-rich submontane calciphytic beech forest (Hordelymo-Fagetum lathyretosum) was fenced for an ecosystem research project in 1980. Within this area a large transect (GT) of 2.81 ha with 281 10x10 m quadrats has been laid out as a permanent plot to study natural dynamics. From 1981 to 2011 every 10 years flora and vegetation have been recorded in detail (vertical structure, estimate of cover degree of all species in %, vegetation mapping). The results over the three decades are presented in tables of herb layer composition, as well as quantitative distribution maps of selected species and vegetation maps. Already within the first decade a shrub layer mainly of young trees has developed in parts of the transect. Some changes in the herb layer were observed. A frequency table with all 83 species found within 30 years (Table 1) shows many plants (33) with decreasing tendency besides a stock of constant species. Allium ursinum, Cardamine bulbifera, Dryopteris carthusiana, Hedera helix, and Neottia nidus-avis were the only species showing a pronounced increase. Different types of single species dominance or mixture were mapped out, with the key species Aconitum lycoctonum, Allium ursinum, Anemone nemorosa, and Mercurialis perennis. - For a long time the antagonism of Allium (distinct increase) and Mercurialis (strong decrease) was particularly striking, resulting in a strong increase of the A Ilium ursinum dominance type within the three decades. While on the microscale of quadrats a pronounced change of the floristic composition could be recognized, on the mesoscale of the total stand floristic constancy could also be found. - The discussion reviews possible causes and interpretations for the ascertained changes. Apart from local causes such as fencing and competitive power of Allium ursinum, comparison with the literature yields some more global trends. For a long time deciduous forests with no or negligible silvi-cultural treatment have undergone increasing canopy closure, leading to a shadier and more humid microclimate. Since some decades nutrient-demanding species may have benefitted from nitrogen deposition. Within the last two decades increasing effects of global warming such as a prolonged growing season have been observed. As a new phenomenon the dieback of ash by fungal attack has been described.