What we know about wildlife outcomes of the conservation reserve program: A meta-analysis

Abstract

The Conservation Reserve Program (CRP) is one of the most extensive private-land conservation programs in the United States, aimed at mitigating habitat loss and supporting biodiversity in agricultural landscapes. Individual studies of CRP effects on wildlife report mixed results, necessitating a comprehensive synthesis. We conducted a meta-analysis and vote-counting assessment of 96 studies (1009 case studies, i.e., individual analyses of a wildlife response to a CRP predictor variable) to evaluate effects on wildlife density, occurrence, reproduction, habitat use, and species diversity. Formal meta-analyses were performed for wildlife density and avian nest success. We found CRP generally benefited wildlife, with vote counting indicating positive effects in 32% of all comparisons (i.e., including comparisons to any type of non-CRP land) and in 64% of comparisons to cropland. Formal meta-analysis indicated avian nest success was significantly higher on CRP lands compared to non-CRP lands, but CRP enrollment did not consistently increase wildlife density, likely due to species-specific and ecological factors we did not account for. The literature was strongly biased toward birds (90% of case studies), with limited research on mammals, invertebrates, amphibians, and reptiles. High heterogeneity in effect sizes suggests that variation in conservation practices, study methodologies, and ecological contexts plays a critical role in shaping measured wildlife responses to CRP. Our results demonstrate CRP provides important benefits to wildlife, particularly by enhancing avian reproductive success. However, variation in wildlife effects highlights the need for studies that incorporate more detailed information on CRP management practices and increased research on non-avian taxa. Addressing these gaps may provide additional information allowing for the implementation of improved conservation strategies and maximize CRP's ecological benefits in agricultural landscapes.