Benefits of Conservation Easements to Biodiversity: Evidence from Wetland Birds

This study investigates the ecological benefits of conservation easements on bird populations, specifically those established around wetlands. Wetlands, which covered only 116.4 million acres (approximately 6% of U.S. land) by 2019, have experienced a 50% increase in loss rates since 2009 due to drainage and agricultural conversion. In response, the U.S. Department of Agriculture’s Natural Resources Conservation Service has obligated over $1.8 billion to preserve nearly 800,000 acres via agricultural and wetland easements, with the 2018 Farm Bill allocating roughly $450 million annually to the Agricultural Conservation Easement Program (ACEP). We provide causal estimates of how wetland easements affect bird relative abundance and species richness, accounting for variations in easement intensity, timing, and hydrological boundaries. Our data span 2003 through 2023 and include granular eBird observations—one of the most comprehensive citizen-science bird datasets available, offering novel geographic and temporal resolution—that we use to construct annual HUC12-level indices of relative abundance and species richness by conditioning on observer effort, expertise, and seasonality. We supplement these observations with the National Conservation Easement Database for spatial records of CREP, ACEP, and EQIP easements; the National Land Cover Database for high-resolution wetland and land-cover classifications; PRISM climate data (temperature and precipitation) to control for weather influences; and CropIndex land use and crop price information to capture adjacent agricultural pressures. Our empirical strategy proceeds in two steps. First, we generate subwatershed-level indices of bird abundance and richness using eBird checklists, differentiating between breeding and non-breeding seasons to capture habitat sensitivity. Second, we implement a staggered difference-indifferences design: treated subwatersheds with wetland easements are compared to matched control subwatersheds in the same HUC8 watershed that have not yet received easements. Matching on pre-treatment trends and covariates mitigates confounding and spillover concerns, while the two-period comparison isolates changes before and after easement implementation. Preliminary findings suggest notable heterogeneity in bird indices over time, with subwatersheds of higher initial richness tending to maintain or increase their relative abundance. Although definitive results are forthcoming, we anticipate that wetland easements will demonstrate positive but uneven effects on biodiversity measures. By providing timely, causal estimates of conservation easement efficacy, this research contributes to economic valuation of wetland ecosystem services and informs policymakers and land managers aiming to optimize investments in habitat protection.