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Plant and Soil

, Volume 293, Issue 1–2, pp 121–132 | Cite as

Large-scale causes of variation in the serpentine vegetation of California

  • James B. Grace
  • Hugh D. SaffordEmail author
  • Susan Harrison
Original Paper

Abstract

Serpentine vegetation in California ranges from forest to shrubland and grassland, harbors many rare and endemic species, and is only moderately altered by invasive exotic species at the present time. To better understand the factors regulating the distribution of common/representative species, endemic/rare species, and the threat of exotics in this important flora, we analyzed broad-scale community patterns and environmental conditions in a geographically stratified set of samples from across the state. We considered three major classes of environmental influences: climate (especially precipitation), soils (especially the Mg2+/Ca2+ ratio), and the indirect influences of climate on soils. We used ordination to identify the major axes of variation in common species abundances, structural equation models to analyze the relationship of community axes and endemic and exotic species richness to the environment, and group analysis techniques to identify consistent groupings of species and characterize their properties. We found that community variation could be explained by a two-axis ordination. One axis ranged from conifer forest to grassland and was strongly related to precipitation. The second axis ranged from chaparral to grassland and had little relationship to current environmental conditions, suggesting a possible role for successional history. Precipitation and elevation were respectively the largest influences on endemic and exotic richness, followed by Mg2+/Ca2+. The results also support the idea that long-term precipitation patterns have altered the Mg2+/Ca2+ ratio via selective leaching, resulting in indirect influences on endemics (positive) and exotics (negative) but not affecting the abundances of common species. We discuss implications of these findings for the conservation of the California serpentine flora.

Keywords

California Cluster analysis Ordination Serpentine Structural equation modeling Vegetation 

Notes

Acknowledgements

We thank V. P. Claassen, R. O’Dell, D. McGahan, R. J. Southard, and R. Zierenberg for helpful discussions on the relationship between rainfall and soil chemistry. We also acknowledge the reviews of two anonymous colleagues.

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Copyright information

© Springer Science+Business Media B.V. 2007

Authors and Affiliations

  • James B. Grace
    • 1
  • Hugh D. Safford
    • 2
    Email author
  • Susan Harrison
    • 3
  1. 1.US Geological Survey, National Wetlands Research Center LafayetteUSA
  2. 2.USDA Forest Service, Pacific Southwest RegionVallejoUSA
  3. 3.Department of Environmental Science and Policy UC DavisDavisUSA

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