Reducing cultivation risk for at-risk species: Predicting outcomes of conservation easements for sage-grouses

Abstract

Conversion of native habitats to cropland is a leading cause of biodiversity loss. The northeastern extent of the sagebrush (Artemisia L.) ecosystem of western North America has experienced accelerated rates of cropland conversion resulting in many declining shrubland species including greater sage-grouse (Centrocercus urophasianus). Here we present point-process models to elucidate the magnitude and spatial scale of cropland effects on sage-grouse lek occurrence in eastern Montana, northeastern Wyoming, North Dakota and South Dakota. We also use a non-parametric, probabilistic crop suitability model to simulate future cropland expansion and estimate impacts to sage-grouse. We found cropland effects manifest at a spatial scale of 32.2 km² and a 10 percentage point increase in cropland is associated with a 51% reduction in lek density. Our crop suitability model and stochastic cropland build-outs indicate 5–7% of the remaining population in the US portion of sage-grouse Management Zone I is vulnerable to future cropland conversion under a severe scenario where cropland area expands by 50%. Using metrics of biological value, risk of conversion, and acquisition cost to rank parcels, we found that a US $100 M investment in easements could reduce potential losses by about 80%, leaving just over 1% of the population in the study are vulnerable to cropland expansion. Clustering conservation easements into high-risk landscapes by incorporating landscape-scale vulnerability to conversion into the targeting scheme substantially improved conservation outcomes.