Refine
Document Type
- Article (3) (remove)
Language
- English (3) (remove)
Has Fulltext
- yes (3)
Is part of the Bibliography
- no (3) (remove)
Keywords
- eutrophication (3) (remove)
Wet grasslands once covered a large area in the lowlands of northern Germany, but have declined since several decades as a result of land use intensification. Permanent plot data from such grasslands in the region that would allow to assess the extent of changes in species composition and richness are still rare. Here, we present a re-visitation study of 52 quasi-permanent plots from the Stedinger Land area in the basin of the river Weser near Bremen, comparing quadrat data between 1948 and 2015. In 1948, the grasslands were characterized by species typical of wet, moderately fertile grasslands belonging to the Bromo-Senecionetum aquatici (Bromion racemosi), including 15 species currently classified as threatened. Until 2015, the vegetation had changed strongly: almost all indicators of wet grasslands had either declined or completely vanished, whereas more nutrient-demanding species of less wet soils had increased, especially grasses. The cumulative number of species had declined by 50%, while mean plot species richness had decreased by 64.6%, mainly resulting from the pronounced loss of many herbs. A comparison of mean Ellenberg indicator values suggested that the plots had become drier, but also more base- and nutrient-rich, most likely triggered by the intensification of land use with drainage and fertilization as well as more frequent and earlier cutting. Our study reflects the dramatic loss of plant species diversity in wet grasslands over the past 60−70 years in areas not preserved and properly managed, and it documents the need for protecting remnants of these grasslands and for restoring wet grassland areas by re-wetting, nutrient removal and the transition to a less intensive land use.
In the Westphalian Basin (North-Rhine Westphalia, Germany), 176 relevés of hedgerows first surveyed during the 1970s were reassessed in 2009 and 2010, and the floristic differences between these two time points were compared. The results were used to analyse the impact of exogenous factors on the species community composition using multivariate statistics (non-metric multidimensional scaling). Significant changes were found within all of the communities along the first axis of the ordination, and, in most cases, increasing average temperatures were best correlated with these alterations. However, based on the considerable evidence found, the alterations induced by land-use change and the intensification of agriculture appear to be the inducing factors.
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.