Sudden Oak Death Risk Assessment

for Special Status Vertebrates in Washington, Oregon and California

Sudden Oak Death (SOD) derives its name from the mortality that it produces in tanoaks (Lithocarpus densiflorus) and certain species of true oaks (Quercus spp.). These species are important components of many western forests and woodlands, providing habitat and food for a diversity of wildlife[i]. Sudden Oak Death affects many other plants besides oaks and SOD-associated mortality threatens the functional integrity of these ecosystems, through its impact on plant and animal communities.

At present it is difficult to predict the course of infection in any given forest or stand. Factors ranging from host genetics to microclimate influence the expression of disease in ways we are only beginning to understand. Similarly, it is impossible to predict with any certainty how wildlife species will respond. Nevertheless it is likely that SOD will have consequences for many creatures—not only for familiar vertebrates but also for many obscure but ecologically crucial invertebrates as well. The present report is based on a series of models, including state GAP and wildlife-habitat relationship models, which predict the distribution of selected plant and animal species and bioclimatic models that predict the susceptibility of regional ecosystems to SOD. This report uses these models to suggest where the habitats of special status[ii] vertebrates may be at risk of infestation with SOD. In addition to these models, data from the scientific literature and other sources such as NatureServe and AmphibaWeb[iii] were incorporated to estimate the extent to which particular species, subspecies or populations might be at risk.

We examined the predicted distributions of all special status mammals, birds, reptiles, and amphibians native to California, Oregon, and Washington to determine the extent to which their habitats might be at risk of SOD infestation. For California we used a risk model developed by Metenmeyer et al [iv] (below). Because no detailed risk maps had been developed for Oregon or Washington when this project was initiated, we constructed a risk layer for each state (below). Further details on the methods are available in the report.

The results reported here comprise a first, coarse-grained attempt to predict risk associated with SOD based on biological models and on SOD’s impact in a limited area over a relatively short period of time. We hope our findings will help identify areas of ignorance and focus attention on the zoological breadth of what may be at risk as a result of this exotic forest disease.

[i] Standiford, R. B. 2002. California's oak woodlands. Baltimore, MD, Johns Hopkins University Press.

[ii] In this study, special status includes all Federal and State Endangered, Threatened, Sensitive, and Candidate species, subspecies, and populations (taxa).

[iii]NatureServe. 2005. NatureServe Explorer: An online encyclopedia of life [web application]. Version 4.6. NatureServe, Arlington, Virginia. Available http://www.natureserve.org/explorer  AmphibiaWeb: Information on amphibian biology and conservation. [web application]. 2005. Berkeley, California: http://amphibiaweb.org/.

[iv] Meentemeyer, R. et al. 2004 Mapping the risk of establishment and spread of sudden oak death in California. Forest Ecology and Management 200: 195–214