Trade-offs between biodiversity and soil carbon storage in grasslands due to cattle grazing

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Grasslands provide ecosystem goods and services (EGS), including: carbon storage, forage for livestock and biodiversity. The primary use of most grasslands is livestock grazing, and while grasslands evolved with grazing (i.e. bison), it can alter plant communities and ultimately affect multiple EGS. But rarely has the provision of multiple EGS been examined simultaneously. Thus, this program will examine the effects of grazing on the relationships and trade-offs among EGS with a focus on the role of grazing driven plant shifts in mediating these effects. We ask 1) what is the relationship among multiple EGS at multiple scales as affected by livestock, and 2) what are the roles of plant species in responding to grazing and affecting responses in EGS. The responses of individual EGS to grazing have been studied, however the pattern of trade-offs among EGS less so. It is often assumed that plant productivity and soil carbon are correlated. However, there are weak and highly noisy relationships between these variables and for some plant species the relationship between diversity, productivity and carbon do not follow these patterns. We will measure these patterns at small scale to relate plant species composition to localized EGS and large scale (pasture management) to examine affects resulting from altered landscape heterogeneity. A trait-based approach will be used to examine the functional role of plants in driving effects on EGS. Plants are key providers of EGS, and individual species may be better providers of different EGS or respond differently to grazing. To understand the effects of grazing on EGS we will measure plant traits that are directly related to ecosystem function (e.g. decomposition rate of leaves) and response traits, such as sensitivity to grazing. These traits will be linked to grassland community composition and ecosystem function, as well as preference by livestock. We will follow this approach with functional "knock-out" experiments designed to examine the impacts of grazing and global change process on EGS. This program will begin resolving how grazing alters multiple EGS through plant community changes. Such research is critical as societal awareness of grasslands increases, and policy to increase soil carbon storage is implemented through grazing management, which may have unintended consequences for biodiversity. Second, it will provide a mechanistic understanding of how individual plant species, through their traits, both respond to grazing and lead to changes in soil carbon storage in grasslands. We currently have an incomplete and sometimes opposing set of patterns in which grazing may or may not be beneficial for grassland ecosystems and ultimately these effects are driven by the selection of different plant species by grazing animals that leads to changes in their relative abundance, but why a particular species shift alters EGS is not always clear.