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Volume 86, Issue 3 p. 295-311
Article

Ecological effects of extreme drought on Californian herbaceous plant communities

Stella M. Copeland

Corresponding Author

Stella M. Copeland

Department of Environmental Science and Policy, University of California, Davis, California, 95616 USA

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Susan P. Harrison

Susan P. Harrison

Department of Environmental Science and Policy, University of California, Davis, California, 95616 USA

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Andrew M. Latimer

Andrew M. Latimer

Department of Plant Sciences, University of California, Davis, California, 95616 USA

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Ellen I. Damschen

Ellen I. Damschen

Department of Zoology, University of Wisconsin, Madison, Wisconsin, 53706 USA

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Anu M. Eskelinen

Anu M. Eskelinen

Department of Environmental Science and Policy, University of California, Davis, California, 95616 USA

Department of Ecology, University of Oulu, Oulu, Finland

Department of Physiological Diversity, Helmholtz Center for Environmental Research – UFZ, German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, Deutscher Platz 5e, D-04103 Leipzig, Germany

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Barbara Fernandez-Going

Barbara Fernandez-Going

Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, California, 93106 USA

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Marko J. Spasojevic

Marko J. Spasojevic

Department of Biology and Tyson Research Center, Washington University in St. Louis, St. Louis, Missouri, USA

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Brian L. Anacker

Brian L. Anacker

Open Space and Mountain Parks Department, City of Boulder, Boulder, Colorado, 80303 USA

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James H. Thorne

James H. Thorne

Department of Environmental Science and Policy, University of California, Davis, California, 95616 USA

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First published: 10 May 2016
Citations: 63
Corresponding Editor: J. M. Levine.

Abstract

Understanding the consequences of extreme climatic events is a growing challenge in ecology. Climatic extremes may differentially affect varying elements of biodiversity, and may not always produce ecological effects exceeding those of “normal” climatic variation in space and time. We asked how the extreme drought years of 2013–2014 affected the cover, species richness, functional trait means, functional diversity, and phylogenetic diversity of herbaceous plant communities across the California Floristic Province. We compared the directions and magnitudes of these drought effects with expectations from four “pre-drought” studies of variation in water availability: (1) a watering experiment, (2) a long-term (15-yr) monitoring of interannual variability, (3) a resampling of historic (57-yr-old) plots within a warming and drying region, and (4) natural variation in communities over a broad geographic gradient in precipitation. We found that the drought was associated with consistent reductions in species richness and cover, especially for annual forbs and exotic annual grasses, but not with changes in functional or phylogenetic diversity. Except for total cover and cover of exotic annual grasses, most drought effects did not exceed quantitative expectations based on the four pre-drought studies. Qualitatively, plant community responses to the drought were most concordant with responses to pre-drought interannual rainfall variability in the 15-yr monitoring study, and least concordant with responses to the geographic gradient in precipitation. Our results suggest that, at least in the short term, extreme drought may cause only a subset of community metrics to respond in ways that exceed normal background variability.