Chronic nitrogen (N) deposition is a threat to biodiversity that results from the eutrophication of ecosystems. We studied long-term monitoring data from 28 forest sites with a total of 1,335 permanent forest floor vegetation plots from northern Fennoscandia to southern Italy to analyse temporal trends in vascular plant species cover and diversity. We found that the cover of plant species which prefer nutrient-poor soils (oligotrophic species) decreased the more the measured N deposition exceeded the empirical critical load (CL) for eutrophication effects (P = 0.002). Although species preferring nutrient-rich sites (eutrophic species) did not experience a significantly increase in cover (P = 0.440), in comparison to oligotrophic species they had a marginally higher proportion among new occurring species (P = 0.091). The observed gradual replacement of oligotrophic species by eutrophic species as a response to N deposition seems to be a general pattern, as it was consistent on the European scale. Contrary to species cover changes, neither the decrease in species richness nor of homogeneity correlated with nitrogen CL exceedance (ExCLemp N). We assume that the lack of diversity changes resulted from the restricted time period of our observations. Although existing habitat-specific empirical CL still hold some uncertainty, we exemplify that they are useful indicators for the sensitivity of forest floor vegetation to N deposition.

Atmospheric nitrogen (N) pollution is considered responsible for a substantial decline in plant species richness and for altered community structures in terrestrial habitats worldwide. Nitrogen affects habitats through direct toxicity, soil acidification, and in particular by favoring fast-growing species. Pressure from N pollution is decreasing in some areas. In Europe (EU28), overall emissions of NO x declined by more than 50% while NH 3 declined by less than 30% between the years 1990 and 2015, and further decreases may be achieved. The timescale over which these improvements will affect ecosystems is uncertain. Here we use 23 European forest research sites with high quality long-term data on deposition, climate, soil recovery, and understory vegetation to assess benefits of currently legislated N deposition reductions in forest understory vegetation. A dynamic soil model coupled to a statistical plant species niche model was applied with site-based climate and deposition. We use indicators of N deposition and climate warming effects such as the change in the occurrence of oligophilic, acidophilic, and cold-tolerant plant species to compare the present with projections for 2030 and 2050. The decrease in N deposition under current legislation emission (CLE) reduction targets until 2030 is not expected to result in a release from eutrophication. Albeit the model predictions show considerable uncertainty when compared with observations, they indicate that oligophilic forest understory plant species will further decrease. This result is partially due to confounding processes related to climate effects and to major decreases in sulphur deposition and consequent recovery from soil acidification, but shows that decreases in N deposition under CLE will most likely be insufficient to allow recovery from eutrophication.

Aims: River gravel bars are endangered habitats in Europe. However, classification schemes of their vegetation and habitat types differ among European countries, and they are even ignored in some national schemes. This causes problems in conservation planning, monitoring and management. Hence we aimed at building the first unified vegetation classification for river gravel-bar habitats across European mountain systems. Location: Europe. Methods: In total 4,769 vegetation plot records of river gravel-bar plant communities were collected from national, regional or private databases, digitized from the literature and newly collected in the field. A hierarchical classification expert system with formal definitions of vegetation types was created. The definitions combined the criteria of presence or cover of groups of species with similar ecology or single species narrowly specialized to a particular gravel-bar habitat. The TWINSPAN classification was applied to early-successional vegetation types to check whether the classification based on formal definitions was supported by the results of unsupervised classification. Similarity patterns among vegetation types were visualized using the detrended correspondence analysis (DCA) ordination. Results: Early-successional and scrub gravel-bar vegetation types were respectively classified into two classes: Thlaspietea rotundifolii and Salicetea purpureae. Eleven associations and four alliances (Calamagrostion pseudophragmitae, Epilobion fleischeri, Salicion cantabricae and Salicion eleagno-daphnoidis) were defined formally. Based on a critical revision, some associations or alliances defined in the previous literature were merged or discarded. The main gradient in variability within the gravel-bar vegetation is connected with the altitudinal gradient, biogeographical variation, local hydromorphological processes and various successional changes. Conclusions: The first unified and formalized classification system of the European mountain river gravel-bar vegetation was created, and species composition, ecology 2 of 27 | Applied Vegetation Science KALNÍKOVÁ et AL. 1 | INTRODUC TI ON Gravel bars of mountain stream beds and banks are azonal habitats that host specialized flora and specific vegetation types. They are typical of wandering or braided river systems occurring from glacial river floodplains in the alpine belt to broad floodplains in the piedmonts. They develop on rivers with significant variation in discharge and are maintained by torrents that are bringing new sediments and regularly disturbing or rearranging river banks. Gravel bars occur preferably in places where the strong current suddenly slows down, allowing the deposition of the particles released by bank erosion in the upstream

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Staszewski, T., Uziębło, A. K., Kubiesa, P., Łukasik, W. 2012: Comparative studies of the spruce tree stand in the Tatrzański National Park. -Beskydy, 5 (1): 27-36The paper presents the results of an investigation carried out at a permanent plot in spruce stand of the Tatrzański National Park in the years 1998-2006. Concentrations of phytotoxic gases in the air together with the load of acidifying compounds reaching the forest soil were characterized. The forest ecosystem response was evaluated by analysing the chemistry of the needles, changes in health status of trees and floral composition. Neither exceedances of the critical SO 2 and NO 2 concentration levels in the air nor the critical load of acidity were found. Only ozone concentration level was recognised as a potential threat to the trees. Heavy metal concentrations in spruce needles represented levels concerned as non-hazardous for the health status of the tree stand. The use of the spruce needles as a cumulative bioindicator showed the presence of PAHs with carcinogenic properties in the air. The investigated spruce stand belongs to the slightly damaged class, however in the period of 1998-2004 a deterioration of the spruce trees condition was observed expressed by a diminishing number of health trees. A comparative investigation carried out in the years 2001 and 2006 proved stability of the floral composition at the permanent plot.