Grassland biodiversity is vulnerable to land use change. How to best manage semi-natural grasslands for maintaining biodiversity is still unclear in many cases because land-use processes may depend on environmental conditions and the indirect effects of land-use on biodiversity mediated by altered abiotic and biotic factors are rarely considered. Here we evaluate the relative importance of the direct and indirect effects of grazing intensity on plant communities along an elevational gradient on a large topographic scale in the Eastern Carpathians in Ukraine. We sampled for two years 31 semi-natural grasslands exposed to cattle grazing. Within each grassland site we measured plant community properties such as the number of species, functional groups, and the proportion of species undesirable for grazing. In addition, we recorded cattle density (as a proxy for grazing intensity), soil properties (bare soil exposure, soil organic carbon, and soil pH) and densities of soil decomposers (earthworms and soil microorganisms). We used structural equation modelling to explore the direct and indirect effects of grazing intensity on plant communities along the elevation gradient. We found that cattle density decreased plant species and functional diversity but increased the proportion of undesirable species. Some of these effects were directly linked to grazing intensity (i.e., species richness), while others (i.e., functional diversity and proportion of undesirable species) were mediated via bare soil exposure. Although grazing intensity decreased with elevation, the effects of grazing on the plant community did not change along the elevation gradient. Generally, elevation had a strong positive direct effect on plant species richness as well as a negative indirect effect, mediated via altered soil acidity and decreased decomposer density. Our results indicate that plant diversity and composition are controlled by the complex interplay among grazing intensity and changing environmental conditions along an elevation gradient. Furthermore, we found lower soil pH, organic carbon and decomposer density with elevation, indicating that the effects of grazing on soil and related ecosystem functions and services in semi-natural grasslands may be more pronounced with elevation. This demonstrates that we need to account for environmental gradients when attempting to generalize effects of land-use intensity on biodiversity.

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24Grassland biodiversity is among the most vulnerable to land use. How to best manage 25 semi-natural grasslands for maintaining biodiversity is still unclear in many cases because 26 processes may depend on environmental conditions and indirect effects are rarely considered. 27 Here we evaluate the relative importance of direct and indirect effects of grazing intensity on 28 plant communities along an elevational gradient on a large topographic scale in the Eastern 29 Carpathians in Ukraine. We sampled 31 semi-natural grasslands exposed to cattle grazing in 30 two years. Within each grassland site we measured plant community properties such as the 31 number of species, functional groups, and the proportion of undesirable weeds. In addition, 32 we recorded cattle density (as proxy for grazing intensity), soil properties (bare soil exposure, 33 soil organic carbon, and soil pH) and densities of soil decomposers (earthworms and soil 34 microorganisms). We used structural equation modelling to explore direct and indirect effects 35 of grazing intensity on plant communities along the elevation gradient. We found that cattle 36 density decreased plant species and functional diversity but increased the proportion of 37 undesirable weeds. Some of these effects were directly linked to grazing intensity (i.e., 38 species richness), while others (i.e., functional diversity and proportion of undesirable weeds) 39 were mediated via bare soil exposure. Although grazing intensity decreased with elevation, 40 the effects of grazing on the plant community did not change along the elevation gradient. 41Generally, elevation had a strong positive direct effect on plant species richness as well as a 42 negative indirect effect, mediated via altered soil acidity and decreased decomposer density. 43 Our results indicate that plant diversity and composition are controlled by the complex 44 interplay among grazing intensity and changing environmental conditions along elevation. 45Furthermore, we found lower soil pH, organic carbon and decomposer density with elevation, 46 indicating that the effects of grazing on soil and related ecosystem functions and services in 47 semi-natural grasslands may be more pronounced with elevation. This demonstrates that we 3 48 need to account for environmental gradients when attempting to generalize effects of land-use 49 intensity on biodiversity. 50 51 53 4 55 Introduction 56 Grasslands cover more than 40% of the global terrestrial area [1] and are among the 57 most species-rich habitats in Europe [2]. As a result of their high biodiversity, grasslands 58 provide crucial ecosystem functions and services beyond that of livestock forage production 59 [3-7]. However, grassland biodiversity compared to the diversity in other ecosystem types is 60 among the most vulnerable to human impact, particularly to land-use change [8]. Of 61 extraordinary importance for biodiversity are semi-natural grasslands [2,6,7], which are 62 remnants of habitats created by tree cutting, haymaking, or low-intens...