Chaparral is a dominant vegetation community in the southern California mountains. It is characterized by evergreen, sclerophyllous shrubs adapted to a Mediterranean climate and infrequent wildfire. However, there is limited documentation on how the loss and gradual regrowth of chaparral communities affects watershed runoff and nutrient loads or how severe drought conditions may alter community recovery. We collected aboveground vegetation data over seven years (2010, 2011, 2016) following a 2008 and a 2009 fire in Santa Barbara county to characterize which species recover immediately after fire and how community composition changed between the early and later post-fire years including across a severe four-year drought (2011-2016). Aboveground sampling was administered at eight “burned” sites, with twelve 1x1 m plots plus three 15 m transects per site, and compared with three “unburned” sites. Measurements included: presence/absence in plots, percent cover by species, aboveground biomass (wet and dry), water content, and carbon and nitrogen content. We specifically looked for evidence of drought kill in the 2016 survey. Field measurements were correlated with AVIRIS imagery to predict watershed scale recovery of biomass, water, and nitrogen.
Forb cover (%) was greatest in 2011 as expected. Shrub cover (%) continually increased from 2010 to 2016. Ceanothus megacarpus was the only shrub species to increase in cover all seven years. Resprouting species, as a group, declined in cover 2010-2011, and then some species increased while others declined during the drought. Resprouters like A. fasciculatum and some manzanita species increased, while C. betuloides, H. arbutifolia, and M. laurina decreased. Nonetheless, drought kill was rare across the plots.
There was a strong correlation between field recorded moisture content and AVIRIS calculated equivalent water thickness (“live fuel moisture”) in 2010 and 2011, with a stronger relationship in forb dominated sites compared to shrub dominated sites. A similar correlation was found between total aboveground biomass and equivalent water thickness. Field measured nitrogen was well estimated by AVIRIS data.
Monitoring chaparral recovery will provide additional information on succession and how these communities respond during drought conditions. At our sites, shrubs were resistant to drought, although drought may have caused the decline in some species. Correlating AVIRIS imagery with field measurements promotes our ability to monitor chaparral regrowth in remote locations and will allow for non-destructive, longer-term monitoring across larger portions of the landscape.