Landscape Variability Underpinning the Social-Ecological System in the Nebraska Sandhills

abstract:The Nebraska Sandhills comprises the largest stabilized sand-dune formation in the Western Hemisphere and the major recharge area for the High Plains groundwater aquifer. The grass-stabilized sand dunes are interspersed with wet valleys where groundwater is at or near the surface. The dominant land use is cattle grazing, and grass cover is likely key to dune stability. Grass cover, however, is likely highly dependent on landscape position and moisture status. We focused this study on an area managed for cattle grazing and wild hay production for over a century, representative of the relatively low-intensity land use throughout the central Sandhills. We used field plots, drone imagery, and analyses of satellite imagery, together with drought indices, to document dune-to-valley patterns. Results indicate that warm-season (C4) grasses and bare ground are more prevalent on dune tops while cool-season (C3) grasses dominate valley bottoms, especially in the groundwater-irrigated hay meadows. Thirty-five years of Landsat imagery revealed higher greenness (Normalized Difference Vegetation Index—NDVI) values in lowlands compared to uplands. Finally, greenness of both valleys and dunes responded to drought, as measured by the Standardized Precipitation-Evaporation Index, but dunes showed stronger correlation than did valleys to short-term drought. Overall, our study suggests that landscape complexity in the Nebraska Sandhills is a key element controlling its function and is likely key to the sustainability of the social-ecological system.