UC Irvine

Aim: Precipitation controls the production of semi-arid plants through various mechanisms that operate at a range of time-scales. Short-term variation in precipitation affects vegetation through adjustments in plant physiology and leaf phenology, whereas long-term effects are mediated by plant establishment and mortality, community composition and disturbance regimes. Our goal is to use remote sensing observations to separate the short- and long-term effects of variation in precipitation on ecosystem production. Location: California, USA. Methods: We used time series of gridded absorbed photosynthetically active radiation (APAR) to quantify the short- and long-term responses of diverse ecosystems to variation in precipitation across large productivity and precipitation gradients. We investigated the relationships between temporal sensitivity of APAR to interannual variation in precipitation and mean annual precipitation (MAP), ecosystem properties and disturbance. Results: APAR increased with precipitation both interannually within locations and across locations with MAP. The slope of the interannual relationship, which reflects the sensitivity of APAR to short-term fluctuations in precipitation, varied with climate, vegetation type and structure, and time since disturbance. The interannual APAR sensitivity decreased from c. 0.5 MJ m-2mm-1 at a MAP of 300mm year-1 to less than 0.05 MJ m-2mm-1 at 1000mm year-1. The slope of the spatial relationship, which reflects the long-term sensitivity of APAR to climate, decreased from c. 2.5 MJ m-2mm-1 at 300mm year-1 MAP to c. 0.6 MJ m-2mm-1 at 1000mm year-1. The initial physiological and leaf area effects of a precipitation shift were amplified five-fold over time by gradual changes in population density and species composition. Main conclusion: The impact of a hydroclimatic shift on the primary production, structure and function of California's terrestrial ecosystems depends heavily on time-scale and how rapidly changes in plant population density and community composition can occur. © 2013 John Wiley & Sons Ltd.