While we have learned much from ecological research on plant water resources, many unknowns remain in our understanding of how fog influences ecosystems. 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. 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. To determine the effects of fog on live fuel moisture, meteorological measurements, drought indices, and fog deposition were merged into principal components and incorporated into a linear mixed effects model of live fuel moisture loss rate during the summer drought. We hypothesized that given the patterns of summer fog deposition, lower elevation plant communities and species with shallow roots were more likely to uptake fog water. Additionally, we predicted that fog would significantly affect plant flammability in these same species more than species found at higher elevations.
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 was a significant correlate of live fuel moisture loss rate for the three sage scrub species tested, but not for the chaparral species. It is likely that fog ameliorates drought for species that experience consistent fog during the summer months. In coastal California, summer fog can be an important water source for some species and reduce live fuel moisture loss rates during the summer drought. Regions of the world with consistent fog deposition may be less susceptible to wildfires than would be predicted by traditional models of fire danger.