Talk, IAVS 2015 - 58th Annual Symposium of the International Association for Vegetation Science, Brno: 2015-07-19 - 2015-07-24
The emission of acidifying airborne pollutants, which peaked in Europe and North America between the 1960’s and mid-1980’s, had detrimental ecological effects on large spatial scale. Legal regulations in the late-1980’s led to a considerable reduction of emitted atmospheric pollutants, the main source of acidification. The reduction of acidifying pollutants, which induced a recovery of terrestrial ecosystems, caused a significant decrease of scientific interest for this topic during the last decade. However, the ecological repercussions of acidification may interact with emerging physical stressors like gradual climate warming or extensive drought events. The legacy of the ecological heritage of 20th century acidification could evoke complex responses of biodiversity in face of climate change. Here, we investigate the interaction of the respective abiotic stressors and their impact on community composition and biodiversity for spring bogs in Central Europe. Additionally, we focus on positive feedbacks of these abiotic stressors with biotic system elements (i.e. species) which are able to biotically modify the biochemical environment and, thus, may create inertia to adaptation for other species. Therefore we studied species dominance relations and composition as well as discharge hydrochemistry of more than 100 spring bogs in the mountain ranges of Central Germany over a period of 25 years (1989-2014). Both, dominance relations and community composition were found to be mainly driven by water temperature and by the concentration of acidification-related elements (Al, Cd, Ca and Mg). As a result of acidification three groups of spring plant communities could be identified which significantly differed in their ecological responses (resilience, elasticity) to the extreme summer drought of 2003. Furthermore, we observed significant positive feedbacks between past anthropogenic acidification and the biogenic acidification caused by the increasing occurrence of peat moss species (Sphagnum spp.), which lead to lasting shifts of anthropogenically acidified communities towards even more acidophilous communities. Our studies on spring bogs, which are a neglected but very sensitive ecosystem, show that complex interactions between past and present abiotic stressors as well as biotic system elements affect patterns of beta-diversity until today although the initial abiotic trigger arose more than two decades ago.