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To protect ecosystems and their services, the critical load concept has been implemented under the framework of the Convention on Long-range Transboundary Air Pollution (UNECE) to develop effectsoriented air pollution abatement strategies. Critical loads are thresholds below which damaging effects on sensitive habitats do not occur according to current knowledge. Here we use change-point models applied in a Bayesian context to overcome some of the difficulties when estimating empirical critical loads for nitrogen (N) from empirical data. We tested the method using simulated data with varying sample sizes, varying effects of confounding variables, and with varying negative effects of N deposition on species richness. The method was applied to the national-scale plant species richness data from mountain hay meadows and (sub)alpine scrubs sites in Switzerland. Seven confounding factors (elevation, inclination, precipitation, calcareous conte nt, aspect as well as indicator values for humidity and light) were selected based on earlier studies examining numerous environmental factors to explain Swiss vascular plant diversity. The estimated critical load confirmed the existing empirical critical load of 5e15 kgNha⁻¹yr⁻¹ for (sub)alpine scrubs, while for mountain hay meadows the estimated critical load was at the lower end of the current empirical critical load range. Based on these results, we suggest to narrow down the critical load range for mountain hay meadows to 10-15 kgNha⁻¹yr⁻¹.

Roth, T., Kohli, L., Rihm, B., Meier, R., & Achermann, B. (2017). Using change-point models to estimate empirical critical loads for nitrogen in mountain ecosystems. Environmental Pollution, 220, 1480–1487. https://doi.org/10.1016/j.envpol.2016.10.083

Thanks to a close cooperation between the field team of the biodiversity monitoring of Switzerland BDM and the staff of Swiss Soil Monitoring Network NABO an extensive soil sampling campaign could be carried out. Between 2011 and 2015 topsoil samples at levels down to 20 cm at approximately 1200 locations evenly spread over Switzerland were taken during the field campaign of the BDM indicator «species diversity in habitats» (Z9). For the first time, a nationwide harmonised soil data set that includes all main land use types is now available for a comprehensive evaluation. Preliminary results of the measured pH levels reveal the expected differences according to geology. The comparison of vascular plants, mosses and mollusks of the biodiversity monitoring with measured soil parameters allow the identification of soil properties which have a substantial impact on the species diversity in the various habitats of Switzerland. A first comparison between topsoil pH and the reaction value R of plants reveals its applicability as a proxy variable for soil acidity.

Meuli, R. G., Wächter, D., Schwab, P., & Zimmermann, R. (2017). Connecting biodiversity monitoring with soil inventory information-A Swiss case study. BGS Bulletin 38 (2017):65-69. Link to PDF.

Aim The aim was to investigate the relationship between climate, topography and soil pH, as well as vegetation structure and the beta diversity of plants, butterflies and birds; and to investigate the correlations of (woody) plant beta diversity with animal beta diversity.

Location Switzerland (central Europe).

Methods We used pairwise Sørensen dissimilarity as measure of total beta diversity and partitioned it into its turnover and nestedness components. Variation partitioning was used to assess the independent and cumulative effects of environmental predictors, with vegetation
structure being derived from airborne light detection and ranging (LiDAR) data. We also checked for independent effects of plant and woody plant beta diversity on butterfly and bird beta diversity, respectively, and for independent effects of spatial distance on beta diversity.

Results Climate emerged as the strongest statistical predictor of beta diversity across taxonomic groups, with large independent effects on species turnover. Climate effects were most pronounced for plants, followed by butterflies and birds. We also found large independent effects of vegetation structure on total beta diversity and its turnover component across taxonomic groups, particularly for birds. Plant and woody plant beta diversity substantially improved the predictions of butterfly and bird beta diversity, respectively. Spatial distance had hardly any independent effect on beta diversity.

Main conclusions Climate is a stronger filter for plant communities than for butterfly and bird communities, which are more affected by vegetation structure, probably owing to associated resources and niches. Vegetation structure is a crucial predictor of beta diversity, and therefore contiguous and detailed 3-D habitat structure data are highly relevant to further our understanding of niche-based community assembly. Plant and animal beta diversity appear to be non-independent, suggesting that differences in the response times of interacting taxa should be accounted for in environmental change impact assessments on biodiversity.

Zellweger, F., Roth, T., Bugmann, H., & Bollmann, K. (2017). Beta diversity of plants, birds and butterflies is closely associated with climate and habitat structure. Global Ecology and Biogeography, 26(8), 898–906. https://doi.org/10.1111/geb.12598

Aim Biological invasions are today the second-largest global threat for biodiversity. Once introduced, exotic plant species can modify ecosystem composition, structure and dynamics, eventually driving native species to local extinction. Among the groups of organisms, most likely to be directly affected by exotic invasive plants are herbivorous insects, such as butterflies, which strongly depend on plants throughout their life cycle. However, it remains unclear whether invasive plants have a negative or a positive effect on butterfly diversity at a landscape scale.

Location Switzerland.

Methods Using an extensive inventory (393 sites across Switzerland) of both butterfly and invasive plants, we explore the impact of 31 invasive black listed plant species on local butterfly richness. We further identify each butterfly species’ response to invasive plants (i.e. positive, neutral or negative) and analyse the functional and phylogenetic characteristics of these different groups of species.

Results Our results indicate that butterfly richness negatively correlates with an increase in invasive plant richness. When studying the individual response of each butterfly species to the number of invasive plants, we found that no single butterfly is profiting from invasive plant species, while 28 butterfly species (24%) suffer from the presence of invasive plants. We further show that the species negatively affected are on average less mobile than the unaffected species and that they are phylogenetically clustered.

Main conclusions Our results present evidences of the influence of invasive species on other trophic levels and interaction networks. We further highlight that a lack of management efforts for mitigating invasive plant impacts threatens specific sections of the functional and phylogenetic diversity of butterflies.

Gallien, L., Altermatt, F., Wiemers, M., Schweiger, O., & Zimmermann, N. E. (2017). Invasive plants threaten the least mobile butterflies in Switzerland. Diversity and Distributions, 23(2), 185–195. https://doi.org/10.1111/ddi.12513