Abstract
AbstractAimPrecipitation 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.LocationCalifornia, USA.MethodsWe 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.ResultsAPAR 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−2 mm−1 at a MAP of 300 mm year−1 to less than 0.05 MJ m−2 mm−1 at 1000 mm 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−2 mm−1 at 300 mm year−1 MAP to c. 0.6 MJ m−2 mm−1 at 1000 mm 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 conclusionThe 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.
Highlights
Water availability exerts a strong control over net primary production (NPP) in arid and semi-arid regions, regulating the year-to-year variation in NPP within individual sites and shaping the long-term distribution of NPP across the landscape (Knapp & Smith, 2001; Zavaleta et al, 2003; Harpole et al, 2007; Hsu et al, 2012; Ruppert et al, 2012)
The absorbed photosynthetically active radiation (APAR) sensitivity to interannual precipitation peaked in areas with intermediate variability in precipitation, such as grassland and desert shrubland, and was muted in wet areas with dense forest vegetation and in dry areas with very sparse vegetation (Figs 3 & 5; Knapp & Smith, 2001)
The high interannual APAR sensitivity observed for most grassland and shrubland sites presumably reflects selection for plants that capitalize on episodic increases in precipitation, as would be expected given California’s variable precipitation regime
Summary
Water availability exerts a strong control over net primary production (NPP) in arid and semi-arid regions, regulating the year-to-year variation in NPP within individual sites and shaping the long-term distribution of NPP across the landscape (Knapp & Smith, 2001; Zavaleta et al, 2003; Harpole et al, 2007; Hsu et al, 2012; Ruppert et al, 2012). Short-term fluctuations in water input, associated with seasonal or interannual variation in precipitation, affect plant production through rapid adjustments in plant physiology, phenology, leaf growth and crown expansion or dieback (Penuelas et al, 2004; Zhang et al, 2005). Long-term shifts in water input, associated with climate variation, affect plant production through gradual changes in plant establishment and mortality, population density and species composition, disturbance regime and soil development (Kratz et al, 2003; Suttle et al, 2007). A clear distinction between the implications of short- versus long-term change in precipitation, and an improved understanding of the amplitude and reversibility of rapid versus gradual ecological response, are needed to anticipate the ecological consequences of climate change (Easterling et al, 2000; Walther et al, 2002; Smith et al, 2009)
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