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Within the last 30 years the role of nitrogen in Central European forests has changed fundamentally from limiting resource to environmental problem. As the retrospective tracking of nutrient availability by soil chemical and biogeochemical measurements faces serious problems, bioindication based on understorey species composition is indispensable for monitoring broad-scale eutrophication. Based on a broad survey of more than 100,000 forest vegetation plots accessible in electronic data-bases from Germany and adjacent countries, we calculated unweighted average Ellenberg nutrient values (mN) as a proxy of plant-available macronutrients. Based on the quantiles of the frequency distribution of mN in a regionally stratified sample, we define five trophic classes, which can be used to compare dimensionless mN values. We studied spatial patterns of average nutrient values within 17 regions and compared the periods from 1899 to 1975 and 1976 to 2006. After 1975 eutrophic (mN > 5.67) and hypertrophic (mN > 6.28) conditions were common everywhere except in the Alps and Saxony-Anhalt, but very oligotrophic conditions (mN < 3.44) were still widespread in regions with nutrient-poor bedrock. Before 1975 mN of plots had been lower than after 1975 in all but the southeastern regions. Between the pre- and post-1975 data the proportion of hypertrophic plots increased from 5.7 to 11.8%, and that of very oligo-trophic plots decreased from 14.6 to 8.3%. To remove bias resulting from uneven distribution, the dataset was stratified by five tree layer dominance types, period and region and resampled. In pre-1975 plots medians of mN increased in the order Pinus sylvestris, Quercus spp., Picea abies, Fagus sylvatica and Alnus spp, whereas the increase of mN was highest in forest types with historically low nutrient values. Therefore, the widespread change in mN must be attributed to the pronounced vegetation changes in Quercus and Pinus stands, indicating the importance of land-use change, i.e. recovery of nutrient cycles after hundreds of years of exploitation through coppicing, grazing and litter use. The analysis confirms eutrophication as a megatrend of modern vegetation change and demonstrates the high research potential of linking vegetation plot databases across large regions.
Between 1996 and 2006 the vegetation succession in drift sands and in blown-out gravel-rich depressions, located in the nature reserve Hulshorsterzand in the central Netherlands, was studied. Within this Natura 2000 habitat (type 2330: inland dunes with open Corynephorus and Agrostis grasslands) so-called lichen steppes are included, famous for their biodiversity, both in flora (cryptogams), and in fauna. With multivariate analysis, the relation between the primary succession, the species composition of the vegetation and the soil quality was studied in three different biotopes i.e. 1. drift sand, 2. blownout gravel-rich depressions and 3. drift sand after management. With a total of up to 34 species, lichen diversity in the study area appeared to be high. Biotope 1, i.e. the pioneer vegetation with Corynephorus canescens on blowing sand, is rather scarce in lichens. Between 1996 and 2006 green algae, C. canescens and Polytrichum piliferum appeared, with the result that much of the former open drift sand area was covered by pioneer stages of the Spergulo-Corynephoretum. If sand stopped blowing in, a combination of P. piliferum with the neophyte Campylopus introflexus occurred. The terminal stages of lichen succession on drift sand, a vegetation with mainly Festuca ovina s.l., Deschampsia flexuosa and reindeer lichens (Cladonia subgen. Cladina), proved to be rather stable. Since 1996 the lichen steppes occurring in biotope 2 were increasingly grass-encroached. Where some sand was still blowing in, lichen diversity did not change much, but gradually C. introflexus increased. However, without sand blowingin, a decreasing lichen cover and loss of some Red List lichens occurred. In general, in this grass-rich vegetation Calluna vulgaris will germinate and gradually a dry heath might develop. However, where dynamics had stopped and Pinus sylvestris seedlings established, succession to a young forest started. Vegetation change from open sand to lichen-rich vegetation is clearly related to a decrease in pH, an increase in organic matter, in % total N and in % total P. The lichen composition is clearly related to this gradient. The applied restoration measures on steep sand dunes in the eastern area, both of cutting pine trees and removing topsoil down to the mineral soil layer, proved to be successful. The sand kept drifting and the pioneer community thriving, including the lichen Stereocaulon condensatum characteristic of pioneer conditions, while the neophytic moss hardly increased between 1996 and 2006.