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Sudden Oak Death

Sudden oak death on Soper-Wheeler lands

Sudden Oak Death is a forest disease caused by the fungus-like micro-organism Phytophthora ramorum and has resulted in widespread dieback of several tree species in California and Oregon forests. It is also the cause of Ramorum blight, which affects the leaves and twigs of numerous other plants in forests and nurseries.


Since the mid 1990s, P. ramorum has caused substantial mortality in tanoak trees and several oak tree species (coast live oak, California black oak, Shreve oak, and canyon live oak), as well as twig and foliar diseases in numerous other plant species, including California bay laurel, Douglas-fir, and coast redwood. The pathogen was also discovered in European nurseries in the mid 1990s, and it has since spread to wildland trees in the U.K. and the Netherlands.


Sudden Oak Death changes the species composition in infested forests and therefore changes how the ecosystem functions. Loss of food sources for wildlife, changes in fire frequency or intensity, and decreased water quality due to an increase in exposed soil surfaces are all potential consequences.

Pathogen Habitat

Redwood planted in Sudden Oak Death area

P. ramorum thrives in cool, wet climates. In California, coastal evergreen forests and tanoak/redwood forests within the fog belt are the primary habitat. Research in California forests has shown that the greatest predictor of P. ramorum is the presence of California bay laurel (Umbellularia californica). Nurseries outside of these cool, moist areas often create microclimates which mimic the preferred environment of P. ramorum and allow it to grow and spread far from the coast.


Currently there aren’t any effective treatments for infected areas. However, careful quarantining of forest products can help reduce the spread of the pathogen.

Soper-Wheeler is currently experimenting with planting redwood in areas devastated by Sudden Oak Death. The broken canopy provides a suitable micro-climate for young redwoods that have yielded promising results in test plots. If successful, redwoods could possibly balance some of the ecological stress created by the pathogen.

For more information on Sudden Oak Death, see www.suddenoakdeath.org

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