Sensitivity of grassland plant community composition to spatial vs. temporal variation in precipitation

Abstract

Climate gradients shape spatial variation in the richness and composition of plant communities. Given future predicted changes in climate means and variability, and likely regional variation in the magnitudes of these changes, it is important to determine how temporal variation in climate influences temporal variation in plant community structure. Here, we evaluated how species richness, turnover, and composition of grassland plant communities responded to interannual variation in precipitation by synthesizing long-term data from grasslands across the United States. We found that mean annual precipitation,(MAP) was a positive predictor of species richness across sites, but a positive temporal relationship between annual precipitation and richness was only evident within two sites with low MAP. We also found higher average rates of species turnover in dry sites that in turn had a high proportion of annual species, although interannual rates of species turnover were surprisingly high across all locations. Annual species were less abundant than perennial species at nearly all sites, and our analysis showed that the probability of a species being lost or gained from one year to the next increased with decreasing species abundance. Bray-Curtis dissimilarity from one year to the next, a measure of species composition change that is influenced mainly by abundant species, was insensitive to precipitation at all sites. These results suggest that the richness and turnover patterns we observed were driven primarily by rare species, which comprise the majority of the local species pools at these grassland sites. These findings are consistent with the idea that short-lived and less abundant species are more sensitive to interannual climate variability than longer-lived and more abundant species. We conclude that, among grassland ecosystems, xeric grasslands are likely to exhibit the greatest responsiveness of community composition (richness and turnover) to predicted future increases in interannual precipitation variability. Over the long-term, species composition may shift to reflect spatial patterns of mean precipitation; however, perennial-dominated systems will be buffered against rising interannual variation, while systems that have a large number of rare, annual species will show the greatest temporal variability in species composition in response to rising interannual variability in precipitation.

Experiment, monitoring, and gradient methods used to infer climate change effects on plant communities yield consistent patterns

“…It stands to reason that thermophilization may be another emergent community property with a relatively strong sensitivity to climate. Although results tend to be more similar when examining synthetic community properties, in situ temporal variability does not always alter community properties in the same direction as predicted by geographic gradients; for example, the effect of rainy years on species richness does not generally mimic the positive relationship between grassland species richness and precipitation across latitudinal gradients (28,29).…”

Responses of soil microbial functional genes to global changes are indirectly influenced by aboveground plant biomass variation

“…Predicting ecosystem responses to global change is a fundamental issue in ecology. It has been well documented that the aboveground plant community is sensitive to precipitation change (Cleland et al, 2013;Eskelinen and Harrison, 2015) and N deposition (Stevens et al, 2004;Clark and Tilman, 2008), particularly in arid and semi-arid grassland ecosystems, where water and N are generally considered to be limiting resources (Harpole et al, 2007;Yang et al, 2011;Xu et al, 2012b). A growing body of evidence suggests that higher precipitation increases plant species richness (Bai et al, 2008;Xu et al, 2015b), whereas N fertilization is reported as the main driver of the loss of species richness (Gough et al, 2000;Stevens et al, 2004;Yang et al, 2011).…”

Climate-driven diversity loss in a grassland community

“…In California, where overall aridity has increased in recent decades (18) and coastal and inland fog have declined dramatically (24,25), aridification is predicted to dominate the effects of climate change on natural vegetation over the coming century (18,19,26). Although directional declines in species richness in western US grasslands in response to long-term drying trends are not yet documented, they may be expected based on evidence that grassland species richness is higher in wetter than drier years, geographical locations, and experimental treatments (27)(28)(29). Seed dormancy, especially by annuals, is likely an important facet of short-term fluctuations in grassland species richness in response to water availability (e.g., ref.…”