The temporal dynamics of a regional flora—The effects of global and local impacts

Abstract

The main trends in changes in the global vascular plant biodiversity are generally considered to be a decrease in rare indigenous species and a spread of invasive plants. In the present paper, the impact of these changes on the flora of the state of Baden-Württemberg (Southwest-Germany) is examined. The data come from a regional floristic mapping project, which consists of two consecutive surveys, dating from 1970 to 1998 and from 2005 to present. In contrast to many other studies, not only a part of the flora or of an ecosystem was studied but the entire vascular plant flora of a region. As the recent survey is not yet completed, samples of 46 out of 1100 grid cells are analysed as a preliminary study on the trends in entire Baden-Württemberg. In the present paper we address the issues (1) whether changes in biodiversity observed in other studies, e.g. decrease of rare native species and increase of invasives, affect the flora of Baden-Württemberg, (2) which abiotic factors, i.e. climatic or soil conditions, cause these changes of species diversity.The analysis of the two consecutive surveys revealed a continuing decrease of rare native species and a constant increase of neophytes, thus reflecting the global trends. Many extinction events happened before 1970, some already in the 19th century. Changes in land use and urbanisation of former rural regions are two important factors for these changes. A statistic analysis using Ellenberg indicator values revealed the nitrogen input from agriculture and the effects of global warming as further potential causes for these trends.