Biological Invasions

, Volume 10, Issue 8, pp 1243–1255 | Cite as

Impact of sudden oak death on tree mortality in the Big Sur ecoregion of California

  • R. K. Meentemeyer
  • N. E. Rank
  • D. A. Shoemaker
  • C. B. Oneal
  • A. C. Wickland
  • K. M. Frangioso
  • D. M. Rizzo
Original Paper

Abstract

The Big Sur ecoregion in coastal California is a botanically and ecologically diverse area that has recently experienced substantial mortality of oak (Quercus spp.) and tanoak (Lithocarpus densiflorus) trees due to the emerging forest disease sudden oak death, caused by the invasive pathogen Phytophthora ramorum. In response to the urgent need to examine environmental impacts and create management response strategies, we quantified the impact of P. ramorum invasion on tree mortality across the Big Sur ecoregion using high-resolution aircraft imagery and field data. Using the imagery, we mapped all detectable oak and tanoak trees possibly killed by P. ramorum infection within redwood-tanoak forests and mixed oak woodlands. To validate and improve our remote assessment, we quantified the number, size, and infection status of host trees in 77 field plots (0.25 ha). The field data showed that our remote assessment underestimated mortality due to the occurrence of dead trees in the forest understory. For each forest type, we developed regression models that adjusted our remote assessments of tree mortality in relation to field observations of mortality and local habitat variables. The models significantly improved remote assessment of oak mortality, but relationships were stronger for mixed oak woodlands (r2 = 0.77) than redwood-tanoak forests (r2 = 0.66). Using the field data, we also modeled the amount of dead tree basal area (m2) in relation to the density of mapped dead trees in mixed oak woodlands (r2 = 0.73) and redwood-tanoak forests (r2 = 0.54). Application of the regression models in a GIS estimated 235,678 standing dead trees in 2005 and 12,650 m2 of tree basal area removed from the ecoregion, with 63% of mortality occurring in redwood-tanoak forests and 37% in mixed oak woodlands. Integration of the remote assessment with population estimates of host abundance, obtained from an independent network of 175 field plots (0.05 ha each), indicated similar prevalence of mortality in redwood-tanoak forests (20.0%) and mixed oak woodlands (20.5%) at this time. This is the first study to quantify a realistic number of dead trees impacted by P. ramorum over a defined ecological region. Ecosystem impacts of such widespread mortality will likely be significant.

Keywords

Big Sur Emerging infectious disease Forest disease Invasive species Landscape epidemiology Phytophthora ramorum Plant-pathogen Tree mortality Remote sensing 

Notes

Acknowledgements

We thank B.L. Anacker, G. Garner, and M. Kozanitas for assistance with field work; K. Merg and the UC Santa Cruz Landels-Hill Big Creek Reserve for use of researcher and overnight facilities; M. Borchert and the USDA Forest Service for logistical support; and B.L. Anacker for helpful contributions to the preparation of the manuscript and coordination support for field data collection. This research was supported by grants from the USDA Forest Service (Pacific Southwest Research Station) and the National Science Foundation (EF-0622677).

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Copyright information

© Springer Science+Business Media B.V. 2007

Authors and Affiliations

  • R. K. Meentemeyer
    • 1
  • N. E. Rank
    • 2
  • D. A. Shoemaker
    • 1
  • C. B. Oneal
    • 1
  • A. C. Wickland
    • 3
  • K. M. Frangioso
    • 3
  • D. M. Rizzo
    • 3
  1. 1.Department of Geography and Earth SciencesUniversity of North Carolina at CharlotteCharlotteUSA
  2. 2.Department of BiologySonoma State UniversityRohnert ParkUSA
  3. 3.Department of Plant PathologyUniversity of CaliforniaDavisUSA

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