Distribution, dispersal, and management of the invasive legume Lupinus polyphyllus in the UNESCO Biosphere Reserve Rhön

Abstract

Semi-natural grasslands are one of the most prominent remnants of the historical cultural landscapes of Central Europe. Due to their century-long land-use history, they are remarkably diverse ecosystems. However, they are threatened by different aspects of global change, such as land abandonment, agricultural intensification, and the spread of invasive species. One species of particular concern for grassland managers is the invasive garden lupine (Lupinus polyphyllus Lindl.), which is among the most widespread invaders in European semi-natural grasslands. This thesis assesses the ecology of L. polyphyllus concerning its distribution, germination, and dispersal in semi-natural grasslands of the UNESCO Biosphere Reserve Rhön against the background of a more efficient management of the species. To this end, the spatio-temporal distribution of L. polyphyllus was assessed by combining mapping via aerial photographs and field mapping. A germination experiment under laboratory and common garden conditions was carried out to assess the potential of L. polyphyllus seeds of different development stages to be dispersed by management. Finally, a field experiment was carried out to explore seed dispersal by mowing machinery and migratory sheep, concerning both the invader and typical grassland species. Data analysis was performed using different univariate and multivariate statistical approaches. This thesis documented a considerable spread of L. polyphyllus in the study area and supported the finding that landscape structure is highly relevant for plant invasions. Particularly, the size of a grassland patch and its distance to the next road were deciding factors for the L. polyphyllus invasion. Concerning the germination of L. polyphyllus, it became evident that both germination capability and timing of germination depend on management, as late cut black seeds showed high germination percentages and germinated under favorable spring conditions. Thus, the production of these seeds should be avoided. Furthermore, seed dispersal by mowing machinery and sheep endozoochory was explored in the heavily invaded grasslands of the study area. It could be shown that both dispersal vectors transport different parts of the regional species pool, and different functional traits are favored by each vector. For the long-term conservation of semi-natural grasslands, several dispersal vectors should be made available by grassland managers. Dispersal of L. polyphyllus can be mitigated given adequate management (i.e. before ripe seeds are produced). In invaded grasslands, an adaptation of the management to the phenology of L. polyphyllus is to be advised. Additionally, management in semi-natural grasslands should consider the landscape context more thouroghly. To this end, the development of holistic land-use concepts that include the management of patches of semi-natural grassland, neighboring land-use and edge habitats such as roadsides are necessary.