Santa Clarita Valley Ecological Conservation: Identifying Oak Woodland Infested with the Goldspotted Oak Borer in the Santa Clarita Valley Using Earth Observations

The recent arrival of the invasive Goldspotted Oak Borer (GSOB; Agrilus auroguttatus) into Newhall Pass, California threatens oak woodlands in the Santa Clarita Valley and risks spreading into the Santa Monica Mountains. Without early intervention, previous GSOB infestations have led to widespread oak mortality. Currently, the Mountains Recreation and Conservation Authority and the Resource Conservation District of the Santa Monica Mountains, our two partners, employ ground surveys for GSOB detection and decision-making processes. Comprehensive surveys are constrained by rugged terrain and reliance of visible symptoms, which typically develop several years after the initial infestation, to identify infested trees. This study evaluated the feasibility of using Earth observations—specifically, the Airborne Visible InfraRed Imaging Spectrometer-3 (AVIRIS-3), Landsat 8 Operational Land Imager (OLI) &Thermal Infrared Sensor (TIRS), Landsat 9 OLI-2 &TIRS-2, and Sentinel-2 Multispectral Instrument (MSI) to assess the extent of GSOB infestations in the Santa Clarita Valley, identify regions susceptible to future spread, and examine historical landcover changes linked to GSOB activity. We demonstrated the capability of low altitude 2.9m-resolution AVIRIS-3 hyperspectral imagery to accurately identify infested oaks (74.7%) within the study area. We further identified areas in Los Angeles and Ventura Counties at high risk for future infestation and illustrated that the10m-resolution Sentinel-2 NDVI time series did not show the historical spread of infestation. The tools and models developed in this project offer valuable insights for future decision-making aimed at early detection and mitigation of the GSOB spread to ultimately protect oak ecosystems.