Monitoring the Impacts of Severe Drought on Southern California Chaparral Species using Hyperspectral and Thermal Infrared Imagery

Abstract

Airborne hyperspectral and thermal infrared imagery acquired in 2013 and 2014, the second and third years of a severe drought in California, were used to assess drought impacts on dominant plant species. A relative green vegetation fraction (RGVF) calculated from 2013-2014 Airborne Visible Infrared Imaging Spectrometer (AVIRIS) data using linear spectral unmixing revealed seasonal and multi-year changes relative to a pre-drought 2011 reference AVIRIS image. Deeply rooted tree species and tree species found in mesic areas showed the least change in RGVF. Coastal sage scrub species demonstrated the highest seasonal variability, as well as a longer-term decline in RGVF. Ceanothus species were apparently least well-adapted to long-term drought among chaparral species, showing persistent declines in RGVF over 2013 and 2014. Declining RGVF was associated with higher land surface temperature retrieved from MODIS-ASTER Airborne Simulator (MASTER) data. Combined collection of hyperspectral and thermal infrared imagery may offer new opportunities for mapping and monitoring drought impacts on ecosystems.

High N, dry: Experimental nitrogen deposition exacerbates native shrub loss and nonnative plant invasion during extreme drought

“…Over 5 years of below‐average rainfall and record high temperatures, native shrub cover was greatly reduced due to dieback of branches and entire shrubs. This is consistent with previous reports of CSS shrub mortality during extended drought (Minnich & Dezzani, ) and recent documentation of vegetation dieback in southern California during the same study period using hyperspectral and infrared aerial imagery (Coates et al., ). Similar widespread drought‐induced shrub loss was previously documented in Spanish shrublands (Peñuelas et al., ).…”

“…Since 2011 and as of this writing, California has experienced an exceptionally severe drought driven by below-average precipitation combined with record high temperatures (Fahrenkamp-Uppenbrink, 2015;Griffin & Anchukaitis, 2014). This has resulted in widespread increases in plant water stress at the landscape level (Asner et al, 2016) and dieback of woody vegetation, including CSS (Coates, Dennison, Roberts, & Roth, 2015). As in other Mediterranean regions, rainfall in southern California is highly variable from year to year, as well as within years (Haston & Michaelsen, 1997).…”

Extensive drought‐associated plant mortality as an agent of type‐conversion in chaparral shrublands

“…At one chaparral site, stand density was reduced by > 60%, primarily due to mortality that occurred during winter 2014, and some species exhibited > 90% mortality (Venturas et al ., ). The same patterns were also apparent at broader scales (Coates et al ., ).…”

Seasonal changes in tissue‐water relations for eight species of ferns during historic drought in California

“…The climate is mediterranean, characterized by long, dry summers and cool, wet winters (Aschmann, 1973; Cowling et al, 2005). Chaparral shrubs growing in the SMM typically survive 6 to 9 mo with little to no precipitation, but in 2013 they experienced only 28 mm of rain over 10 mo, that led to excessive defoliation and whole plant mortality (Coates et al, 2015). A recent study based on tree ring analysis suggests that the 2012–2014 drought in California was the worst in the last 1200 yr (Griffin and Anchukaitis, 2014).…”