PS 32-197 - Recovery of the dominant shrub species on natural gas well pads in a widespread midlatitude dryland

Abstract: Water-limitation in drylands results in the slow recovery of plant communities following a disturbance. Drylands in the western U.S. are dominated by big sagebrush (Artemisia tridentata), a long-lived and late-successional species which after disturbance, takes years to achieve pre-disturbance levels of biomass, density, and cover. Energy exploration and development is a particularly prevalent disturbance across federal lands in the Intermountain West. However, reclamation—the federally mandated act of rehabilitating an ecosystem from energy development—has been relatively unsuccessful in returning native plant communities to pre-disturbance states on oil and gas well pads. We sought to examine the effectiveness of reclamation by simulating the recovery of big sagebrush biomass and density in the first 150 years following well pad development. We collected vegetation and soils data at the Jonah natural gas field in southwestern Wyoming to use as inputs to a stochastic, individual plant-based, ecohydrological model (STEPWAT2). We ran simulations of 200 well pads for each of three seedling establishment treatments, high-establishment (50%), moderate-establishment (10%), and low-establishment (0%). We simulated treatments under historical weather conditions (1980-2010) and under four climate change scenarios, mid-century (2060-2090) and end-century (2070-2100) RCP 4.5 and RCP 8.5, for each of which we chose the median GCM of 13. From the results of these simulations, we compared yearly biomass and density with undisturbed reference areas. Under historical conditions, mean biomass and density of big sagebrush on well pads met and surpassed that of the undisturbed reference areas between simulation years 63 and 101. High-seedling establishment resulted in greater biomass and density than moderate and low-establishment. A comparison of the frequency distributions of biomass and density revealed that the well pads and reference areas had statistically different distributions throughout the entire simulation, but that their distributions were most alike between 110 and 147 years. Moreover, we found that greater mean annual temperature and precipitation under RCP 4.5 and RCP 8.5 resulted in higher simulated biomass overall compared to historical conditions. On average however, biomass and density did not recover earlier than under historical conditions. Our study suggests that while mean big sagebrush biomass and density may return to well pads in under a century, the recovery of big sagebrush stand structure is unlikely within 150 years of disturbance.