Session

In Europe, low-intensity livestock grazing regimes are increasingly used as a tool by managers for maintaining natural and semi-natural grasslands. These regimes help to maintain an open ground canopy and potentially conserve rarer species while increasing the wider biodiversity. It is widely demonstrated that the grazer type and grazing intensity affect the overall structure of grasslands, influencing the distribution of functional traits, however the extent to which these effects relate to species turnover versus intraspecific phenotypic shifts is less understood. For example, more intense grazing typically lowers inflorescence height. How much of this is due to an influx of lower flowering species or a reduction of mean flowering height within the population? An improved understanding of the interplay between these processes under varying grazing regimes would help managers achieve their conservation aims. Here, we investigated the impacts of grazing on the composition and structure of grasses within a long-term (20 years) grazing experiment in the Scottish Uplands. We collected data on grass composition and seven individual-level grass functional traits from 18 plots with three grazing treatments. Multivariate abundance models were used to determine the effect of grazing treatment, plot drainage, and location on grass community composition. Variation between plots was largely due to differences in the relative abundance of widespread species and was driven by plot location, although treatment had marginally significant effects. We then decomposed grass community trait variability to examine the relative roles of species turnover and intraspecific trait variability (ITV) in trait responses to environmental variables and grazing intensities. Our results indicate that ITV is the primary driver of variation across these traits, more than species turnover. Overall, we found that grazing intensity does influence these grass communities but structural changes are largely the results of existing species adapting their trait values to changing levels of grazing rather than community shifts towards species better adapted to that grazing level. This has implications for land managers who can diversify grazing levels in different areas to enhance landscape heterogeneity and biodiversity.