The Nebraska Sandhills comprise the largest stabilized sand dune formation in the Western Hemisphere and the major recharge area for the High Plains groundwater aquifer. The landscape consists of grass-stabilized sand dunes interspersed with wet valleys where ground water is often near or at the surface. The dominant land use is cattle grazing and grass cover is key to the resilience and sustainability of the social-ecological system. We used satellite and drone-based imagery to characterize the dynamics of vegetation greenness (NDVI) and bare ground cover, as it varies in both space and time in this complex landscape. In addition, we used the Standardized Precipitation-Evaporation Index (SPEI), over both short (3 m) and longer (48 m) time periods to understand the key role of moisture as a driver of vegetation and surface water.
Results/Conclusions
Our results suggest that dry periods can result in significant declines in NDVI but that these declines are buffered somewhat in the wet portions of the landscape, the groundwater-irrigated valleys. Furthermore, SPEI, integrated over a 48 m period reveals a multi-decadal wet period, which is likely responsible for historically high levels of ground water in the valleys. Our analysis suggests that both temporal and spatial scales operate in complex ways to control vegetation in this sand dune landscape with short term variation in precipitation controlling cover in uplands, whereas longer term variation in moisture controls cover in lowlands Sustainability of the social-ecological system depends on managers integrating this complex variability.