A new method for jointly assessing effects of climate change and nitrogen deposition on habitats

Abstract

Climate change and nitrogen (N) deposition are among the most important drivers of biodiversity change at a global scale. Although commonly considered separately in applied research, conservation, and policy development, both empirical evidence and modelling studies indicate that these two stressors may act synergistically and trigger a more pronounced biodiversity loss than each of them alone. Interactive effects thus need to be considered in biodiversity conservation. In this study, we propose a new method for jointly assessing risk from both stressors to habitats by combining climate envelope modelling and the evaluation of exceedance of empirical critical loads for eutrophication through N deposition. Based on this approach we can calculate a combined risk metric, which is the scaled exceedance of the N critical load and climatic thresholds in the three-dimensional space of N deposition, temperature, and water limitation. We use a habitat map to project this risk metric for 34 EUNIS habitat types across Austria. Resulting risk maps indicated that about 16 % of the area of these natural and semi-natural habitat types is currently at risk from either N exceedance, drought or warming. Using combinations of future climatic (RCP2.5 and RCP8.5) and N deposition (business as usual, current legislation and maximum feasible reduction) scenarios, we predict that the area at risk might increase to up to 19% until 2050, with risk from N-deposition decreasing and risk from climate change increasing. Combined impacts of both stressors affect only up to 2% of the entire evaluated area, but are much more frequent in particular habitat types such as oligotrophic bogs and subalpine to alpine grasslands. We conclude that this method provides a useful screening procedure to identify and compare areas and habitats under combined risk from both stressors and to thus support prioritization and decision making in biodiversity conservation.