UC San Diego

Coastal sage scrub (CSS) ecosystems are invaluable biodiversity hotspots and carbon sinks, characterized by a Mediterranean-type climate and native plants adapted to drought. With climate change causing increased droughts and wildfires in Southern California, CSS systems are experiencing large-scale disturbances that allow fast-growing invasive species to dominate slower growing natives. In this experiment we used a handheld crop scanner to quantify the normalized difference vegetation index (NDVI) as a proxy for ecosystem-level plant productivity in a partially burned CSS preserve in San Marcos over a two-year period. Part of the preserve recovered with primarily invasive species while another remained native-dominated, producing three experimental areas: burned invaded, burned native, and unburned. We also observed how imposing drought affected each burn treatment area. We found that during the first experimental year, burn treatment affected maximum NDVI value, day of maximum NDVI, and day of green-up. Burned invaded and unburned treatments had the earliest days of maximum NDVI and green-up, as well as the highest maximum NDVI values. The burned native treatment lagged in all three values. Drought treatment only affected day of maximum NDVI, causing a delay across all treatments. In the second year, no significant differences in NDVI were found among burn or drought treatment types, likely owing to the increased recovery of burned areas that approached NDVI levels of the unburned reference area. Our results showed that in the early stages of wildfire recovery, invaded areas can be more productive than native-dominated areas during the wet season, but in as little as two years native vegetation can recover to have similar levels of productivity as invasive-dominated areas. Hence, efforts to remove invasive species and promote native shrub recovery have the potential to enhance long-term CSS carbon storage following wildfire.