Landscape effects on diversity of semi-natural grasslands

We studied how the landscape structure (percentage cover and diversity of surrounding habitats) affects different components of species diversity (alpha, beta and gamma) of vascular plants in semi-natural grasslands in the Slovak Republic. We analyzed all grasslands combined as well as four main types delimited according to their position along a moisture gradient (xerophilous, sub-xerophilous, mesophilous and wet grasslands). We used grassland records stored in the Slovak Vegetation Database. The geographically stratified dataset included 3795 plots with 1221 species of vascular plants. Along with the total number of species in the vegetation plots, we considered the numbers of target grassland species, forest species, archaeophytes, neophytes and species with high fidelity to non-natural habitats. The landscape parameters based on CORINE land cover maps and the National Grassland Inventory, were calculated for plot neighbourhoods of 4 km(2). Spatially constrained rarefaction curves were constructed to examine how different diversity components behave with changing structure of the surrounding landscape. Our study revealed that alpha diversity was affected by both percentage cover and diversity of different habitats in the plot neighbourhood. It increased with increasing proportion or diversity of different natural and semi-natural habitats and decreased with increasing proportion or diversity of non-natural habitats in the surrounding landscape. Beta and gamma diversities showed opposite pattern to that of alpha diversity for most analyzed factors. Alpha diversity in sub-xerophilous and mesophilous grasslands was more susceptible to changes in landscape structure than alpha diversity in xerophilous or wet grasslands. Regression trees and linear or quadratic regression models revealed that in xerophilous or wet grasslands, high alpha diversity was best predicted by a high proportion of ecologically valuable grasslands in the surroundings. In sub-xerophilous and mesophilous grasslands, the best predictor was proportion of natural and semi-natural habitats followed by the proportion of non-natural habitats. The detected pattern regarding alpha, beta and gamma diversity calculated for grassland target species did not differ from the pattern for the whole species assemblage. However, the surrounding landscape affected the number, proportion and cover of species typical of forest or non-natural habitats (including alien species) in the plots. We explain the results by the interplay of two main mechanisms: species pool and spatial mass effects. In our study, the effect of species pool on alpha diversity was stronger than the spatial mass effect. Based on differences indicated in the responses of various grassland types to the surrounding landscape structure, we suggest adoption of community type specific conservation measures (C) 2013 Elsevier B.V. All rights reserved.