A gradual decrease in summer fog along the California coast over the past century may be endangering the region's giant redwoods and affecting the ecology of the area surrounding the trees, according to a study by UC Berkeley scientists.
The redwoods along our coast are highly dependent on fog as a source of water during the summer when water in the ground is scarce," Todd E. Dawson, one of the study's two authors, said in an interview. "Foggy nights are needed to rehydrate the trees that can't tolerate long droughts."
Mature redwoods are unlikely to die if the decrease in fog persists, he said. But fewer seeds are likely to sprout, take root and grow to maturity.
A report is being published today in the online edition of the Proceedings of the National Academy of Sciences.
Dawson and James A. Johnstone, both of Berkeley's Department of Environmental Science, Policy and Management, analyzed 110 years of temperature records gathered by 114 weather stations along the Pacific Coast, and studied fog levels recorded hourly since 1951 at eight local airports from Oregon to the Mexican border.
Using that information, Johnstone calculated that early in the 20th century the frequency of summer fog was 33 percent greater than it has been in recent decades - which could be enough to pose a significant threat of drought stress, particularly to younger trees.
Redwoods are dependent on cool, humid summers, and without enough days of fog the heat becomes too intense for growth, Johnstone said.