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.气候变化与大气氮（N）过量沉降，是影响植物区系生物多样性的主要胁迫因子之一。其中尤为值得关注的是，受《欧洲生境指令》保护的珍贵生境正出现退化。未来，物种潜在分布区由气候驱动的变化（乃至丧失），以及氮素驱动的营养富集，均可能对这类生境构成威胁。本研究针对奥地利境内受欧盟生境指令保护的5类森林生境（共18个森林样地），耦合应用了动态土壤地球化学模型（VSD+）与新型生态位型植物响应模型（PROPS），以此评估未来气候变化与氮沉降将如何影响生境适宜性——生境适宜性被定义为某一样地维持其典型植物物种的能力。评估结果显示，未来气候变化将是奥地利生境适宜性下降的主要驱动因素：预期的气候变化将促使嗜热植物物种的占比上升，同时降低耐冷物种的占比。除上述直接影响外，气候情景下木本生物质对氮的固持作用增强，进而导致土壤氮素耗竭，这使得寡营养物种的出现概率有所提升。因此，即便未假设氮排放量进一步减少，气候变化仍抵消了氮沉降带来的富营养化效应。本研究结果表明，当综合考量多重变化驱动因子时，气候变化可能对森林生境产生积极的附带效应。