Fog and live fuel moisture in coastal California shrublands

9 Across most Mediterranean-type climate regions, seasonal drought desiccates plants, facilitating ignition 10 and the spread of wildfires. Along the California coast, summertime fog has the potential to ameliorate 11 drought conditions and thus reduce plant flammability during a critical time of elevated fire risk. This 12 study investigated the uptake of dry season fog and how it affects live fuel moisture in six dominant shrub 13 species from chaparral and sage scrub plant associations. Fog water uptake was evaluated using stable 14 isotopes of hydrogen and oxygen at several field sites in Santa Barbara County, California. Clear 15 evidence of fog water uptake was identified only in Baccharis pilularis, from the sage scrub association. 16 To determine the effects of fog on live fuel moisture, meteorological variables and indices including fog 17 deposition were combined into principal components and the scores regressed against the live fuel 18 moisture loss rate during the summer drought. Fog deposition slowed rates of live fuel moisture loss for 19 all three sage scrub species tested, but it did not affect the chaparral species. Fog is a more regular 20 occurrence in the sage scrub association and thus it is likely that fog ameliorates drought for species that 21 experience consistent fog during the summer months. In coastal California, summer fog can be essential 22 to plant water relations and reduce live fuel moisture loss rates during the summer drought. 23 Understanding these effects is important in the context of changing climate in southern California and 24 Mediterranean-type climate regions around the world. 25