Finding and defending grassland cores using spatial covariance

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Grasslands are an imperiled ecosystem, and grassland bird abundance is declining across North America. One of the strongest drivers for these declines is woody plant encroachment of grasslands. In the Great Plains and Sagebrush biomes of North America, spatial covariance—a remote sensing metric for tracking boundaries between vegetation types—is emerging as a new method to identify and strategize conservation of grassland cores in the face of woody plant encroachment. Here, we use spatial covariance to predict responses of six declining grassland species, including the iconic upland game bird Northern Bobwhite (Colinus virginiana) responded to spatial covariance at three scales (0.81ha, 7.29ha, and 65.61ha) and tree cover in fragmented grasslands of Arkansas, USA. Tree cover alone was poor predictor of grassland bird occupancy compared to models that included spatial covariance at the 0.81ha and 7.29ha scales. Grassland bird occupancy declined at tree‑grass boundaries (negative spatial covariance at the 0.81ha scale) and increased in grassland cores (near‑zero or slightly positive spatial covariance at the 0.81ha scale). Our results suggest that identifying grassland cores empowers defending core grasslands from woody plant encroachment and then growing cores via active restoration.