Bachelor Thesis

Modellierung der ökologischen Nische quellspezifischer Arten und Prognosen zu ihrer zukünftigen Verbreitung

Johannes Ingrisch (01/2008-12/2008)

Support: Carl Beierkuhnlein, Volker Audorff

Due to the influence of groundwater, forest springs of the siliceous lower mountains ranges of Central Europe are sites with very constant environmental conditions. According to Ellenberg (1996) their water temperature is equivalent to the annual mean temperature of the air. Thus, species that are specialized on springs are only exposed to minor variations in temperature and are regarded as stenothermic. Between species, a varying degree of stenothermy is expected, that is expressed as well by their binding to springs as by the variation of the air temperature to which they are exposed. The species' narrow demands on temperature lead to the assumption, that the temperature influences the occurrence of the species. In this study, I investigate if the influence of the springwater temperature on the occurrence of certain species is larger than the influence of its pHvalue. Furthermore, it is assumed that stenothermic species react particularly sensible to the expected increasing temperature caused by climate change. I investigate these questions on the basis of eight selected spring-specific plant species. Based on hydrological data and vegetation records of 81 forest springs in Fichtelgebirge and Frankenwald, I model the regionally realised niches with regard to the pH and the temperature of the springwater. Climate data and distribution maps of the species are used to model the climatic niches (Climate Envelopes) with regard to the annual mean and seasonality of the air temperature. The models are calculated with Generalized Linear Models (GLM) and Generalized Additive Models (GAM). Using the Climate Envelopes for the annual mean of the air temperature and a regional climate model, predictions are made on the future suitability of the climate in Germany for the studied species. Although the air temperature influences the water temperature, the annual mean temperature of the air and the mean temperature of the springwater are not equal. In all cases the GLMs for the pH explain the occurrence of the plants in the springs better than the corresponding models for the water temperature. This suggests that the influence of the water temperature on the occurrence of the species is weaker than the influence of its pH. Differences in the degree of stenothermy between the species manifest in their area of distribution and in their binding to springs in Germany. For some of the investigated species (e.g. Cardamine amara) the suitability of the climate in Germany declines due to Climate Change and the species could be lost regionally.