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

doi:10.1111/j.1461-0248.2004.00706.x

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Wiley InterScience

Ecology Letters

Volume 8 Issue 2, Pages 127 - 137

Published Online: 17 Dec 2004

Published on behalf of the Centre National de la Recherche Scientifique

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LETTERS

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

John W. Williams ^1,2*, Eric W. Seabloom ^1,3 , Daniel Slayback ⁴ , David M. Stoms ⁵ and Joshua H. Viers ⁶

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
³ Department of Zoology, Oregon State University, Corvallis, OR, USA
⁴ Science Systems & Applications Inc., Biospheric Sciences Branch, NASA Goddard Space Flight Center, Greenbelt, MD, USA
⁵ Institute for Computational Earth System Science, University of California, Santa Barbara, CA, USA
⁶ Information Center for the Environment, Department of Environmental Science and Policy, and John Muir Institute of the Environment University of California, Davis, CA, USA

Correspondence to * E-mail: jww@geography.wisc.edu

KEYWORDS

California • human impacts • land cover change • net primary productivity • species richness • structural equation models

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.

Editor, Helmut Hillebrand Manuscript received 10 May 2004 First decision made 15 June 2004 Second decision made 20 September 2004 Manuscript accepted 1 October 2004

DIGITAL OBJECT IDENTIFIER (DOI)

10.1111/j.1461-0248.2004.00706.x About DOI