By Doreen Walton
Science reporter, BBC News
Redwoods in coastal areas are protected from hot, dry summers
Scientists in California say a drop in coastal fog could threaten the state's famed giant redwood trees.
Their study, published in the Proceedings of the National Academy of Sciences, says such fog has decreased markedly over the past 100 years.
The weather records analysed come from the US National Climate Data Centre.
"Fog prevents water loss from redwoods in summer and is really important for the tree and the forest," said research co-author Professor Todd Dawson.
The team at the University of California, Berkeley was interested in how fog was involved in climate changes on the coast and noticed a drop that they believe could have an effect on the trees.
The scientists say redwoods are concentrated along the coastal areas primarily because they are not as well adapted as other tree species to deal with California's hot summers.
No extinction threat
Dr James Johnstone from the University of Berkeley, who led the research, explained the team had examined tree rings and found signs that reduced fog has had an effect.
"The evidence that you see in the tree rings is consistent with drought stress produced by drought reduction."
Dr Johnstone thinks drought stress could affect the growth of new trees and the plants and animals that depend on the redwoods. But he notes that the negative impact on the tree population is, as yet, unproven.
"We're concerned for certain, we expect some impact on the ecology but we don't have clear evidence that the redwoods are about to go extinct in the near term."
"We need further analysis to find out whether the effects are as we expect," said Dr Johnstone.