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Anthropogenic impacts upon plant species richness and net primary productivity in California

Authors

  • John W. Williams,

    Corresponding author
    1. National Center for Ecological Analysis and Synthesis, 735 State Street, Suite 300, Santa Barbara, CA, USA
    2. Department of Geography, University of Wisconsin, Madison WI, USA
      E-mail: jww@geography.wisc.edu
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  • Eric W. Seabloom,

    1. National Center for Ecological Analysis and Synthesis, 735 State Street, Suite 300, Santa Barbara, CA, USA
    2. Department of Zoology, Oregon State University, Corvallis, OR, USA
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  • Daniel Slayback,

    1. Science Systems & Applications Inc., Biospheric Sciences Branch, NASA Goddard Space Flight Center, Greenbelt, MD, USA
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  • David M. Stoms,

    1. Institute for Computational Earth System Science, University of California, Santa Barbara, CA, USA
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  • Joshua H. Viers

    1. Information Center for the Environment, Department of Environmental Science and Policy, and John Muir Institute of the Environment University of California, Davis, CA, USA
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E-mail: jww@geography.wisc.edu

Abstract

We assess the importance of anthropogenic land-use, altered productivity, and species invasions for observed productivity–richness relationships in California. To this end, we model net primary productivity (NPP) c. 1750 AD and at present (1982–1999) and map native and exotic vascular plant richness for 230 subecoregions. NPP has increased up to 105% in semi-arid areas and decreased up to 48% in coastal urbanized areas. Exotic invasions have increased local species diversity up to 15%. Human activities have reinforced historical gradients in species richness but reduced the spatial heterogeneity of NPP. Structural equation modelling suggests that, prior to European settlement, NPP and richness were primarily controlled by precipitation and other abiotic variables, with NPP mediating richness. Abiotic variables remain the strongest predictors of present NPP and richness, but intermodel comparisons indicate a significant anthropogenic impact upon statewide distributions of NPP and richness. Exotic and native species each positively correlate to NPP after controlling for other variables, which may help explain recent reports of positively associated native and exotic richness.

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