COS 250-2 - Severe disturbance increases sensitivity of production to precipitation in drylands

Abstract: Drylands encompass a diverse array of ecosystems, unified by a scarcity of water, that cover roughly 40% of the Earths terrestrial surface and provide services to around 38% of the world’s population. Given their global extent, drylands play major roles in global energy balance and biogeochemical cycles. Disturbances drive large changes in plant composition and ecosystem functioning in drylands, but current understanding of disturbance effects on plant-water relations is limited due to the small-scale of previous studies and challenges in analyzing effects of disparate disturbances across climate gradients. Here we use 34 years of remote sensing across 5600+ km of natural gas pipeline corridors to understand effects (0-73 years after disturbance) of a uniform disturbance on plant precipitation use efficiency (PUE) and sensitivity of production to interannual deviations in precipitation. Our results indicate that disturbance reduces PUE 2-14% and increases sensitivity of production to precipitation 5-145%. Locations with high mean annual precipitation experienced a larger decrease in PUE and a larger increase in sensitivity to precipitation than areas with low mean annual precipitation. These shifts in plant-water relations are consistent with expected changes in plant functional type, with disturbance replacing late-successional plant forms such as shrubs and trees with early successional herbaceous species that have a higher sensitivity and lower PUE. Effects of severe disturbance on PUE were still significant 60-70 years following a severe disturbance, whereas effects on sensitivity were more ephemeral and lasted 30-50 years. Severe disturbance both decreases net primary productivity and increases its variability in drylands, especially in areas receiving more than 450 mm mean annual precipitation.