Temporal Changes and Spatial Determinants of Plant Species Diversity and Genetic Variation

Abstract

Intensification of agricultural land use during the last century, combined with an increasing level of agrochemicals, has resulted in a decline of both habitat diversity and quality and to simplification and homogenization of Central Europe landscapes. For three agricultural landscapes in Central Germany we investigated (1) the influence of historical and current land-use and landscape structure on plant species diversity patterns in semi-natural habitats as well as on arable fields and (2) the extent to which genetic variation within populations (H e) of the common forest herb Geum urbanum is related to population properties and to present landscape structure. Historical and present floristic field data were analysed in relation to land-use and landscape structure characteristics of the same periods (1950s, 1970s and 2000/2002). Changes in plant species richness and composition during the past 50 years varied among landscapes according to their land-use history and environmental characteristics, but were mostly in favour of ruderal species. Plant species richness for semi-natural habitats was negatively affected by increases in mean patch size of meadows and by increases in phosphorus application. Moreover, the application of mineral fertilizer, especially phosphorus, led to many habitat specialists being replaced by generalist species. Species richness of ‘arable weeds’ was significantly affected at both landscape and regional level by the proportion of semi-natural habitats, habitat diversity and habitat isolation due to landscape homogenization. More intensive land use, and particularly increased nitrogen application, was associated with decreased richness of ‘arable weeds’.