Since its initial appearance in the 1990s, SOD has become the most important cause of mortality of tanoak and susceptible oaks in coastal California forests. However, other agents and environmental factors can cause tanoaks and oaks in these forests to decline and die. Root diseases and wood decay fungi, especially canker rot fungi, can cause relatively high levels of tree decline and mortality in forests whether SOD is present or not.
Mortality due to other agents may also affect trees that are not at risk from P. ramorum. Oaks in the white oak group (table 1-1) are not affected by SOD but are susceptible to most of the same root diseases and decay fungi that affect the SOD-susceptible red oaks. The exotic root rot pathogen Phytophthora cinnamomi causes decline and death of Pacific madrone and California bay and can kill or cause disease in a wide variety of other native species.
Other invasive insects or diseases that are not yet present but could further impact forest health (e.g., the goldspotted oak borer) should be considered in a comprehensive management plan. For example, management practices that prevent the movement of potentially contaminated materials can reduce the risk that the forest will be affected by a variety of invasive agents.