Extreme drought reduces climatic disequilibrium in dryland plant communities

Abstract

High rates of climate change are currently exceeding many plant species' capacity to keep up with climate, leading to mismatches between climatic conditions and climatic preferences of the species present in a community. This disequilibrium between climate and community composition could diminish, however, when critical climate thresholds are exceeded, due to population declines or losses among the more mismatched species. Here, we assessed the effect of an extreme drought event on rich semiarid shrubland communities in the south-eastern Iberian Peninsula. Using a community climate framework, we compared the community climatic disequilibrium before and after the drought episode on three study sites with different levels of precipitation. Disequilibrium was estimated as the difference between observed reference climate and community-inferred climate, calculated as the mean climatic optimum for the species present, weighted by their abundances. We found that extreme drought embedded within a decadal trend of increasing aridity led to a significant reduction in community climatic disequilibrium, and that this reduction was positively related to water deficit (low P/PET values). In contrast, microhabitat variables such as vegetation cover or slope, did not emerge as significant predictors of changes in community climatic disequilibrium. Our study highlights that extreme drought events pushing communities in the same direction as climate trends may decrease community climatic mismatch, leading to communities more adapted to aridity through loss of drought-sensitive

Decrease in climatic disequilibrium associated with climate change and species abundance shifts in Mediterranean plant communities

“…The selected 13 climatic variables—instead of the 19 biovariables commonly used—were chosen to avoid implicit climatic interactions between temperature and precipitation (e.g. temperature of the driest quarter), which may correlate differently between different species distributions, thus hindering subsequent interpretation (Pérez‐Navarro et al., 2021).…”

“…These values can be generally deduced from the distribution of the species (Elith et al, 2006;Franklin, 2010), which allows us to estimate the species-realized niche, although microlocal variability, demographic and adaptive legacies, and the effects of past land uses and disturbances also contribute to current patterns of species abundance (De Frenne et al, 2013;Thuiller et al, 2008). (Bertrand et al, 2011(Bertrand et al, , 2016De Frenne et al, 2019;Devictor et al, 2012;Duchenne et al, 2021;Dullinger et al, 2012;Esperon-Rodriguez et al, 2022;Gaüzère et al, 2017;Lenoir et al, 2013;Pérez-Navarro et al, 2021;Richard et al, 2021), but they are still more observational than experimental. To document the changes in the compositions of plant communities, detailed surveys conducted regularly over long periods are required, such as those provided by field experiments that manipulate climatic conditions (Elmendorf et al, 2015;Komatsu et al, 2019;Peñuelas et al, 2018).…”

“…community approaching an equilibrium with climate) in accordance with the magnitudes of environmental forcing (Richard et al., 2021). Extreme climatic events such as drought or heatwaves may thus induce abrupt changes in community composition promoting sudden decreases in CD (Pérez‐Navarro et al., 2021; Serra‐Diaz et al., 2018). In contrast, changes in climatic means, which act as progressive and constant environmental filters, would lead to gradual decreases in CD (Alexander et al., 2018), although fast decreases due to long‐term accumulated changes would still be possible (Carnicer et al., 2011).…”

“…Long‐term studies addressing the magnitude and change in community composition relative to changes in climate are particularly useful to understand processes leading to vulnerability or adaption of vegetation to climate change. Studies assessing the presence or accumulation of CD have recently become increasingly frequent, from global scales to finer spatial resolutions (Bertrand et al., 2011, 2016; De Frenne et al., 2019; Devictor et al., 2012; Duchenne et al., 2021; Dullinger et al., 2012; Esperon‐Rodriguez et al., 2022; Gaüzère et al., 2017; Lenoir et al., 2013; Pérez‐Navarro et al., 2021; Richard et al., 2021), but they are still more observational than experimental. To document the changes in the compositions of plant communities, detailed surveys conducted regularly over long periods are required, such as those provided by field experiments that manipulate climatic conditions (Elmendorf et al., 2015; Komatsu et al., 2019; Peñuelas et al., 2018).…”

The rate of ecosystem acclimation is the dominant uncertainty in long-term projections of an ecosystem service

“…A synthesis of multi-year drought experiments found little evidence of statistical movement away from the time-series model to the spatial gradient model within a decade 38 . On the other hand, extreme events could accelerate this process if they strongly select against species poorly adapted to future conditions 39 , though many semiarid systems appear resilient to extreme events such as drought 31 . Paleoecological studies document dramatic compositional changes in the recent past, but cannot provide sub-century resolution 40,41 .…”