Agrilus auroguttatus (goldspotted oak borer) is an invasive wood-boring beetle that is killing Quercus agrifolia (coast live oak) in San Diego County and spreading to other counties in Southern California. A. auroguttatus has been in San Diego County for over a decade and has had unknown effects on other aspects of the oak woodlands. These unknown indirect effects were studied in this thesis by looking into understory plants and arthropods under varying crown conditions. Oak demographic changes were important to determine if these oak woodlands are able to replace themselves. Understory plant composition was valuable to understand because changes in composition may alter ecosystem production and future trajectories. Understory arthropods represent many trophic levels, are easy to capture, and respond relatively quickly to changes in the environment. Eight oak woodlands with 14 trees per woodland were studied. General linear models were used to look at specific responses due to differences in crown condition and number of neighboring trees, and non-metric multidimension scaling was used to visualize and evaluate clustering of multiple response variables. We determined that there were distinct plant and arthropod communities under individual oak trees depending on canopy condition. Overall, it appears that oak recruitment may not be in a linear decline after A. auroguttatus enters the system but may be more complicated.
