The Conservation Reserve Program (CRP) has contributed to the restoration of perennial vegetation from former cropland to reduce soil erosion and establish habitat for wildlife across the United States. Although nearly 23 million acres are currently enrolled in CRP, few studies have examined the trophic responses of wildlife to management on these restored habitats across large spatial scales. We addressed this gap by surveying plant, insect, and bird communities on 108 CRP fields across a 635-mm longitudinal precipitation gradient in Kansas. Study fields were split between two Conservation Practices (CP) with relatively low (CP2) and high (CP25) diversity seeding mixes across short, mixed, and tallgrass prairie ecoregions. Approximately half (53) of all fields were also grazed by cattle over two growing seasons to examine the response of study taxa to a disturbance historically common in grasslands, but currently restricted on CRP lands. Through structural equation modeling, we tested the prediction that plant community composition and physical structure would be predicted by the CP and grazing treatments respectively, the response of insect biomass to CP and grazing would be mediated through the plant community, and bird diversity would be largely predicted by the plant community and secondarily by insect biomass.
Results/Conclusions
Despite the difference in seeding mixes, CP did not significantly predict total grass or forb plant cover in CRP plant communities. As expected, grazing did impact indicators of plant physical structure by reducing average litter depth, aboveground plant biomass, average plant height, and total grass cover while increasing variation in plant stand structure. Insect biomass responded negatively to average litter depth and positively to plant height, variation in plant stand structure, and total grass and forb cover in the plant community. Bird diversity was positively predicted by insect biomass and higher on CP25 versus CP2 fields, but no direct relationships were found between plant community indicators and bird diversity to explain this difference between CPs. Altogether, we found evidence for cascading relationships between grazing management, the plant community, and bird diversity, but the explanatory power of these relationships was relatively weak. Our findings may be due in part to inconsistent implementation of CP and additional large-scale geographic factors coinciding with the longitudinal gradient in precipitation. Further investigation within ecoregions may elucidate differing local trophic relationships that will help predict the response of these taxa to management on CRP lands.