Pacific Southwest Research Station

Research Topics Tree Mortality

In California, an estimated 102 million trees have died in California’s national forests due to a combination of climate change, an unprecedented drought, bark beetle infestation and high tree densities. The U.S. Forest Service’s Pacific Southwest Research Station has been working with the Pacific Southwest Region to address the tree mortality issue by using existing science and identifying future research opportunities.

Meanwhile in Hawaii, Rapid Ohia Death is a plant disease killing millions of mature ohia trees on Hawaii Island during the last several years, and is a high priority issue for all natural resource and agricultural agencies working in the state.

Read more about specific impacts from climate, insects and diseases through the research topics below.

Tree Mortality in California

Since 2010, an estimated 102 million trees have died in California’s national forests. An estimated 29 million trees died in 2015 alone, which was the driest of the four years of drought affecting California.

Rapid Ohia Death

Stands of Hawaii's keystone endemic tree, ohia lehua (Metrosideros polymorpha), are experiencing alarming levels of mortality, more than 90 percent in some cases, across large areas of Hawaii Island.

Sudden Oak Death

Phytophthora ramorum, the exotic plant pathogen that causes sudden oak death, has killed more than a million oak and tanoak trees, and is responsible for non-fatal infections in more than 125 plant species.

Climate and Forest Diseases

Extreme weather can kill large expanses of trees by overwhelming them physiologically or compromising their vigor, making them more susceptible to insects and disease.