Abstract
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 NOx 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.
Highlights
IntroductionHuman emissions of reactive Nitrogen (N) have caused numerous environmental problems (Gruber and Galloway 2008)
Atmospheric nitrogen (N) pollution is considered responsible for a substantial decline in plant species richness and for altered community structures in terrestrial habitats worldwide
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
Summary
Human emissions of reactive Nitrogen (N) have caused numerous environmental problems (Gruber and Galloway 2008). Studies addressing climate change as a factor influencing recovery from soil acidification as well as plant available N through its impact on decomposition and N mineralization are rare (Bernal et al 2012, Butler et al 2012, McDonnell et al 2014, Gaudio et al 2015, Rizzetto et al 2016, Dirnböck et al 2017). This highlights a critical need for further research and continuous observation to appreciate the biodiversity benefit of reduced N deposition in European forests (Schmitz et al 2019)
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