Unexpected patterns of sensitivity to drought in three semi-arid grasslands

Abstract

Global climate models forecast an increase in the frequency and intensity of extreme weather events, including severe droughts. Based on multi-year relationships between precipitation amount and aboveground annual net primary production (ANPP), semi-arid grasslands are projected to be among the most sensitive ecosystems to changes in precipitation. To assess sensitivity to drought, as well as variability within the shortgrass steppe biome, we imposed moderate and severe rainfall reductions for two growing seasons in three undisturbed grasslands that varied in soil type and climate. We predicted strong drought-induced reductions in ANPP at all sites and greater sensitivity to drought in sites with lower average precipitation, consistent with continental-scale patterns. Identical experimental infrastructure at each site reduced growing season rainfall events by 50 or 80%, and significantly reduced average soil moisture in both years (by 21 and 46% of control levels, respectively). Despite reductions in soil moisture, ANPP responses varied unexpectedly-from no reduction in ANPP to a 51% decrease. Although sensitivity to drought was highest in the semi-arid grassland with lowest mean annual precipitation, patterns in responses to drought across these grasslands were also strongly related to rainfall event size. When growing season rainfall patterns were dominated by many smaller events, ANPP was significantly reduced by drought but not when rainfall patterns were characterized by large rain events. This interaction between drought sensitivity and rainfall event size suggests that ANPP responses to future droughts may be reduced if growing season rainfall regimes also become more extreme.

Contrasting responses of terrestrial ecosystem production to hot temperature extreme regimes between grassland and forest

“…For the grassland sites, however, there is no significant correlation between mean annual iEVI and T max (R 2 = 0.05, P = 0.64). This is consistent with the fact that vegetation production is more controlled by water availability for grasslands in arid and semi-arid regions and interannual ANPP being related to soil moisture variability (Knapp and Smith, 2001;Knapp et al, 2002;Cherwin and Knapp, 2012). On the other hand, the forest biome is more temperature-limited with regard to productivity, particularly in regions that are not constrained by water, and climatic warming can stimulate vegetation growth through enhancing summer photosynthesis (Churkina and Running, 1998;Nemani et al, 2003;Piao et al, 2007).…”

Consequences of Changing Precipitation Patterns for Ecosystem Functioning in Grasslands: A Review

“…Most studies were conducted in ecosystems with future climate change prognoses indicating decreasing amounts of precipitation (e.g. Miranda et al 2009Miranda et al , 2011Evans et al 2011;Talmon et al 2011;Cherwin and Knapp 2012;Potts et al 2012;Báez et al 2013;Byrne et al 2013). However, some studies, especially those conducted in northern European mesic ecosystems, chose to study precipitation reduction without a clear consensus of climate model predictions (e.g.…”

Drought and Carbon Cycling of Grassland Ecosystems under Global Change: A Review

“…Grasslands have an irreplaceable role, as their contribution to climate change mitigation and adaptation improves land and ecosystem health, resilience, biological diversity regimes, global productivity, and water cycles under future climate scenarios [5]. However, they are also projected to be among the most sensitive ecosystems to drought [6]. Therefore, research on grassland response to drought is of great significance.…”