Currently legislated decreases in nitrogen deposition will yield only limited plant species recovery in European forests

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 NH3 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

Host plant-mediated effects of climate change on the occurrence of the Alcon blue butter¿y (Phengaris alcon).

Among the expected consequences of climate change are shifts in species’ ranges. Most of current methods to predict such shifts in species distributions consider changes in suitability of climatic conditions for existence. With these models, it is possible to indicate the potential distribution of species that would arise under spatial conditions that cause unlimited landscape accessibility and habitat suitability. At the regional scale, however, detailed predictions of changes in species distributions and performance are pivotal for conservation planning. This study aims to predict species occurrences at the regional scale, incorporating demographic processes and dispersal to assess habitat accessibility and suitability in detail. We investigated a system with trophic dependence: the Alcon blue butter¿y (Phengaris alcon) is fully dependent on the occurrence of its host plant species marsh gentian (Gentiana pneumonanthe). We applied a model chain, consisting of a soil and biomass model, a plant species occurrence and dispersal model and a butter¿y metapopulation model. We investigated the effect of future climate change, both under affected and unaffected habitat conditions as determined by host plant occurrence. Our modelled results show that the butter¿ies perform best when habitat conditions remain unaffected by climate change. However, when climate change does affect the occurrence of its host plant species, butter¿y distribution and performance will be deteriorated. This implies that detailed predictions of changes in species distributions and performance should incorporate dispersal, demographic processes and biotic interactions explicitly. Our approach allows for the identi¿cation of locations that are potentially suitable for the measures increasing network robustness for P. alcon

Climate and air pollution impacts on habitat suitability of Austrian forest ecosystems

Climate change and excess deposition of airborne nitrogen (N) are among the main stressors to floristic biodiversity. One particular concern is the deterioration of valuable habitats such as those protected under the European Habitat Directive. In future, climate-driven shifts (and losses) in the species potential distribution, but also N driven nutrient enrichment may threaten these habitats. We applied a dynamic geochemical soil model (VSD+) together with a novel niche-based plant response model (PROPS) to 5 forest habitat types (18 forest sites) protected under the EU Directive in Austria. We assessed how future climate change and N deposition might affect habitat suitability, defined as the capacity of a site to host its typical plant species. Our evaluation indicates that climate change will be the main driver of a decrease in habitat suitability in the future in Austria. The expected climate change will increase the occurrence of thermophilic plant species while decreasing cold-tolerant species. In addition to these direct impacts, climate change scenarios caused an increase of the occurrence probability of oligotrophic species due to a higher N immobilisation in woody biomass leading to soil N depletion. As a consequence, climate change did offset eutrophication from N deposition, even when no further reduction in N emissions was assumed. Our results show that climate change may have positive side-effects in forest habitats when multiple drivers of change are considered.</p