The article talks about the southern California heat islands and how they're eliminating the fog, and then implies that it's a threat to the redwoods because they rely on fog for their water (they actually don't, but I'll get to that in a second). The problem is that the extreme southern tip of the redwoods natural range is in Big Sur in central California. The only redwoods you'll find in southern California, where the heat islands in the article are a problem, have been planted by homeowners and landscapers for decorative effect. Redwoods went extinct in southern California at the end of the last ice age. Even places like Carbon Canyon, which promotes itself as southern California's largest "redwood grove", was actually planted by people during the last century.
The redwoods themselves exist much further north. Except for a small one at San Francisco, none of the northern California coastal towns and cities are large enough to generate a heat island capable of altering the local weather. The redwoods are safe.
And, when it comes right down to it, the redwoods don't actually REQUIRE fog anyway. Trees get most of their water by pulling it from the ground, and redwood trees are no different. The maximum height of a tree is determined by the efficiency of its water lifting ability...trees have to pump water from the roots up to the top, and a tree can't grow higher than it's capable of lifting that water. If a tree can only lift water 50 feet, it can only grow to 50 feet.
Redwood trees are very efficient at lifting water, and it's estimated that they can reach heights exceeding 250-300 feet on root-sourced water alone. The trees use fog-sourced water to supplement this, allowing them to grow even taller. The tallest existing today are around 380 feet, and it's estimated that there were many exceeding 400 feet before logging decimated the original old growth forests. Redwood trees today exist in a wide variety of climates around the world and do just fine.
A reduction in fog would lead to shorter redwood forests, but it wouldn't cause the redwood to go extinct or disappear from its current range.
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