Intra‐seasonal precipitation patterns and above‐ground productivity in three perennial grasslands

Abstract

Summary 1Relationships between above-ground net primary productivity (ANPP) of grasslands and annual precipitation are often weak at the site level, with much of the inter-annual variation in ANPP left unexplained. A potential reason for this is that the distribution of precipitation within a growing season affects productivity in addition to the total amount. 2 We analysed long-term ANPP data for three southern African temperate grasslands (mean annual precipitation ranging from 538 mm to 798 mm) to determine the effects of precipitation event size, number and spacing relative to seasonal totals. 3 Ungrazed, non-manipulated treatments at each site showed contrasting results despite sharing a common, dominant species. At the driest site, a model combining average event size and number of events per growing season provided a substantially better fit to the ANPP data than precipitation amount (seasonal total). At the wettest site, the interval between events was the most important precipitation variable. Precipitation distribution was not important at the intermediate site where amount was the best predictor of ANPP. A limit to the size of precipitation events efficiently utilized for ANPP was evident for the driest site only. 4 At each site, experimental treatments that altered species composition and soil fertility had little effect on precipitation-ANPP relationships. The lack of consistency in the relative importance of the precipitation variables among sites suggests that local, edaphic factors modify precipitation-ANPP relationships. 5 This analysis demonstrates that the distribution and size of precipitation events can affect ANPP independent of precipitation amount. As altered precipitation regimes are forecast by global climate models, the sensitivity of ecosystems to precipitation distribution should be considered when predicting responses to climate change. 6 While mean values of precipitation, and other ecosystem drivers, are typically used to predict function at the level of whole ecosystems, our results show that more complex measures of environmental variability may be required to understand ecosystem function, and to increase the accuracy of predictions of ecosystem responses to global change.

Anticipating changes in variability of grassland production due to increases in interannual precipitation variability

“…Furthermore, under the nonlinear models, ANPP will be decreasing more in dry years than it is increasing in wet years, increasing the frequency of low production years more than the frequency of high production years despite a symmetric increase in the frequency of wet and dry years. These increases in ANPP variability will make primary production more difficult to forecast and could exacerbate existing challenges for natural resource management, especially when combined with alterations in ANPP caused by changes in the annual mean of precipitation (Hsu et al 2012) as well as the intra-annual variability and timing of precipitation (Swemmer et al 2007, HeislerWhite et al 2009, Craine et al 2012.…”

Tallgrass prairie soil fungal communities are resilient to climate change

“…While such changes in the per event volume of rainfall as well as in their frequency have been suggested to lead to rapid alterations in soil processes as well as aboveground community composition Fay et al 2003;Harper et al 2005;Swemmer et al 2007;Fay et al 2011), consequences of such alterations for belowground microbial communities have received comparatively less attention (Chou et al 2008;Zeglin et al 2013). This major gap prohibits our understanding of the soil community responses to changes in soil water that far exceed those witnessed for dominant plants (Huxman et al 2004;Ogle & Reynolds 2004;Schwinning & Sala 2004), tend to be more dynamic, and responsive to pulse events (Austin et al 2004;Ogle & Reynolds 2004;Carbone et al 2011).…”

Responses of gross primary productivity to different sizes of precipitation events in a temperate grassland ecosystem in Inner Mongolia, China

“…Considering that the precipitation events are mostly of small sizes (2-5 mm is the mostly frequent) in arid and semi-arid regions (Li et al, 2001;Loik et al, 2004), the changes in the sizes of precipitation events may have significant consequences on productivity of grassland ecosystems because grasslands are among the most sensitive ecosystems to precipitation changes. Studies have suggested that the effects of precipitation events on productivity may be as important as the annual amount of precipitation (Swemmer et al, 2007;Walter et al, 2012). Therefore, it is imperative to study the response of productivity to different sizes of precipitation events in grassland ecosystems.…”