Ecosystem Threats

Sudden Oak Death is caused by a microscopic pathogen Phytopthora ramorum, a water mold. It is believed to have been brought from eastern Asia through the nursery trade.

The disease is spread to spores via air currents and through human transport of plants. It causes lethal cankers and non-lethal foliar blights and has killed millions of oaks.

Efforts to mitigate the effects of this pathogen have been through early detection and removal of infected plants.

The goldspotted oak borer (GSOB) is a non-native pest first found in San Diego, California in 2004. They feed on the cambium layer of the tree, which affects its ability to transport water and nutrients.

Symptoms include yellowing or dead branches at the tops of trees, discoloration of the trunk, and red/black sap stains.

Efforts to stop GSOB have been to remove infested trees and to prevent the transport of firewood, which can transport GSOB to other locations.

Climate change models have projected that at the current rate of greenhouse gas emissions, oak woodland ranges will be significantly smaller. This is mainly due to higher temperatures causing these species to shift their ranges northward.

Climate change also predicts prolonged drought in California could potentially kill more trees. Although these trees are adapted to drought, longer and repeated periods of drought could cause enough stress to damage and kill these trees.

Rapid population growth and urbanization threatens foothill oak woodlands, which are poorly protected. Studies using birds as an indicator species have shown that large fragments of habitat as well as a diversity of habitats is crucial for the persistence of several bird species. Planning of urban development should take into consider habitat fragmentation to allow for biodiversity to persist.

Invasive species, such as the Barbed Goatgrass, compete with native grasses and reduces their abundance.

Oak woodlands are adapted to regular low burning fires. However, fire suppression in California causes a build-up of fuels that results to severe crown fires today.

Fire exclusion can also lead to conifer encroachment since Douglas-firs are able to expand their ranges into oak woodland habitat. Encroachment can change the flammability of an area by decreasing the number of understory plants and dampening fuel bed flammability. This has lead to a significant loss of oak woodland habitat in Northwestern California.