Spatial and temporal patterns of Ellenberg nutrient values in forests of Germany and adjacent regions - a survey based on phytosociological databases

J. Ewald, S.M. Hennekens, S. Conrad, T. Wohlgemuth, F. Jansen, M. Jenssen, J. Cornelis, H.G. Michiels, J. Kayser, M. Chytry

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29 Citations (Scopus)

Abstract

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 dom-inance 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 exploita-tion 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. Keywords: bioindication, Central Europe, Ellenberg indicator values, eutrophication, nitrogen deposi-tion, soil nutrients, vegetation-plot data
Original languageEnglish
Pages (from-to)93-109
JournalTuexenia
Volume33
Publication statusPublished - 2013

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