Legumes play important roles in grasslands and other nutrient-limited ecosystems by fixing atmospheric nitrogen, facilitating nutrient cycling, and increasing species diversity. For these reasons, legumes are commonly used in seed mixes to restore degraded grasslands; however, the historical distribution and abundance of native legumes is not well understood. We collected vegetation data across the longitudinal precipitation gradient (450-1100 mm annually) in Kansas from 108 Conservation Reserve Program (CRP) sites that were replanted with native species and compared them to 4 native reference sites that had never been plowed. We hypothesized that legume species richness and abundance would be positively related to annual precipitation on native and restored CRP sites. Additionally, we tested whether there was a positive relationship between legume abundance and plant species richness.
Results/Conclusions
Preliminary results suggest that legume species richness and abundance were similar between restored CRP and native reference sites at the lowest annual precipitation levels. In contrast, legume richness increased substantially with annual precipitation on native reference sites, but remained largely unchanged on the restored CRP sites leading to a significant disparity at the highest levels of annual precipitation. This disparity was unexpected given that grasses and non-leguminous forbs increased with annual precipitation on both restored CRP and native reference sites. Legume abundance was positively correlated with annual precipitation, but this relationship was weak and did not differ between restored and native reference sites. Total richness was not correlated with legume abundance regardless of annual precipitation. Although additional native reference sites are needed, our results suggest that as precipitation increases, restoration of legume species on CRP is much lower than expected and these restored CRP sites may not be representative of native prairies.