Diversity-productivity relationships vary in response to increasing land-use intensity

Background and aims: Theoretical and experimental evidence, predominantly from temperate grasslands, demonstrates strong support for a positive relationship between biodiversity and ecosystem functioning. This relationship is likely to be affected by land use drivers that remove vegetation, and/or disturb the soil surface. Our study aimed to examine the links between land use intensity and plant richness, and potential effects on productivity and function. Methods: We examined the impact of mowing, grazing, and mowing plus grazing, on the relationship between plant diversity, and two measures of function; aboveground biomass and soil carbon. Our focus was on Eurasian grasslands, which support a high diversity of plant species, millions of people and their livelihoods, and where livestock grazing and mowing are predominant land uses. We used structural equation modelling to examine the effects of these land use drivers at 371 sites across 100,000 km2 of northern China. Results: Mown sites supported a greater number of plant species than sites that were either grazed, or grazed and mown. Increasing plant richness was associated with greater aboveground biomass and soil carbon when sites were either mown or grazed, but these relationships disappeared when the two land use drivers were combined. Relationships among plant diversity and two measures of function were maintained when we accounted for the spatial differences between sites. Conclusion: Our results demonstrate that additional land use pressure imposed when mowing and grazing are applied together can decouple the positive associations between plant richness and functions. An understanding of these potential effects is important if we are to adopt strategies, such as destocking or reduced mowing, to maintain diverse grassland ecosystems, and their services and functions