Effects of local and landscape factors on grassland plant diversity

Abstract

During the last decades, both the decrease of the area and the fragmentation of semi-natural habitats in Central Europe caused a dramatic decline of biodiversity at local and regional scales. These processes have been largely attributed to the intensification of land-use practices. More recently, the pressure of agricultural intensification has increased by abandonment of many low-productivity semi-natural grasslands that no longer ensured sufficient economic yields. At the local field scale, management intensification resulted in simplified, species-poor grassland communities of low nature conservation value, mainly due to high nutrient input and increased defoliation frequency. At the landscape and regional scale, management intensification had a profound influence by creating relatively simple and homogeneous landscapes dominated by arable fields.In this study, we examined the relative importance of local field management, topographic and landscape variables on grassland species of different management regimes, focusing on both vascular plant species richness and species composition. In addition, we analysed the effect of management regime (meadow vs. pasture) on local-regional patterns of species diversity to provide understanding of the contribution of different management regimes to total observed regional species diversity. Finally, we investigated the relative importance of local and landscape factors on species diversity of mown meadows in an area of the Southern Alps. The data were analysed using different univariate and multivariate statistical procedures.The study was conducted in the rural district of Northeim in Lower Saxony, Germany, and in several districts of the Trento Province, NE Italy. The Northeim district is characterised by a large proportion of arable land and forest, interposed with patchily distributed fragments of grassland. Managed grassland sites were sampled at random, covering a complete gradient from agriculturally improved, species-poor grassland to semi-natural, species-rich grassland that had not experienced agricultural improvement. In the Italian study area, the investigated meadows covered a large gradient of management intensity and elevation.Three major findings emerged from the study concerning the analyses in the rural district of Northeim. (1) Local field management such as low application rates of nitrogen fertilisers contributed to high plant species richness in grasslands, and this effect was much more pronounced for meadows than for pastures. This indicated that high amounts of nitrogen fertilisers caused more competitive exclusion in grasslands protected from herbivory. Moreover, species richness of pastures was positively related to local abiotic site conditions like soils with a low nutrient status and steep slopes. (2) Landscape context showed a strong effect on plant species richness in pastures. Species richness of pastures significantly decreased with increasing percentage of arable land in the surrounding landscape, whereas species richness of meadows was not affected by landscape context. This suggested that both the dispersal by grazing animals and the colonisation of vegetation gaps after disturbance were negatively affected by a high percentage of arable land in the surrounding landscape of pastures. (3) Heterogeneity between the grassland sites at the regional scale contributed the most to overall observed species diversity, indicating considerable differences in plant community composition among the investigated sites. The analysis of management effects revealed that low-to-moderate livestock grazing contributed indirectly to high species richness as pastures were mainly located on steeply sloping grounds with poor soil quality. Analyses of Alpine meadows further revealed that plant species diversity was strongly related to the soil phosphorous content and elevation.Thus, to improve the ability to explain variation in patterns of vascular plant diversity in managed grasslands, there is an urgent need to conduct analyses at multiple spatial scales. This study further implies that future management policies should consider both a reduction of nitrogen fertilisation at the local scale and the maintenance of large scale pasture systems at the regional scale to enable the conservation of a wide diversity of grassland plants.