Fog and live fuel moisture in coastal California shrublands

Abstract

Across most Mediterranean-type climate regions, seasonal drought desiccates plants, facilitating ignition and the spread of wildfires. Along the California coast, summertime fog has the potential to ameliorate drought conditions and thus reduce plant flammability during a critical time of elevated fire risk. This study investigated the uptake of dry season fog and how it affects live fuel moisture in six dominant shrub species from chaparral and sage scrub plant associations. Fog water uptake was evaluated using stable isotopes of hydrogen and oxygen at several field sites in Santa Barbara County, California. Clear evidence of fog water uptake was identified only in Baccharis pilularis, from the sage scrub association. To determine the effects of fog on live fuel moisture, meteorological variables and indices including fog deposition were combined into principal components and the scores regressed against the live fuel moisture loss rate during the summer drought. Fog deposition slowed rates of live fuel moisture loss for all three sage scrub species tested, but it did not affect the chaparral species. Fog is a more regular occurrence in the sage scrub association and thus it is likely that fog ameliorates drought for species that experience consistent fog during the summer months. In coastal California, summer fog can be essential to plant water relations and reduce live fuel moisture loss rates during the summer drought. Understanding these effects is important in the context of changing climate in southern California and Mediterranean-type climate regions around the world.