The Mendocino Coast where we live gets lots of fog – 80 to 120 days a year.
The Earth’s tallest trees, California redwoods, rely on the coastal fog to reach heights of over 300 feet. Coast redwoods (Sequoia sempervirens) are found along a narrow band of California’s northern coast where there is fog. During the summer these red giants take advantage of the fog to capture water out of the air—and summer is the critical growing season for the trees, despite being California’s dry season.
To obtain sufficient moisture for photosynthesis and growth, redwoods have developed leaves shaped like baseball mitts that capture the fog that rolls in by night and languishes through most mornings. From 25 to 40 percent of the moisture in the Redwood eco-system comes from fog. Some of the fog simply covers the leaves and prevents evaporation. But some of it also enters the stomata, or tiny pores, on the leaves and is drawn down through the branches to the roots. This is the reverse of transpiration, the normal flow of water from the roots to the leaves that exists in most trees. Redwoods were the first trees found to move water in both directions.
Fog is not just a vital element for the redwoods—it’s also crucial to the entire redwood forest ecosystem. Some of the moisture drips off the redwood leaves, landing on the forest floor to water the trees and young saplings. It’s not just a drip, drip, drip – the moisture can descend into the ground up to 15 inches deep, and that’s a lot of water.
The fog comes from the Pacific Ocean’s California Current where winds create upwellings that bring cold, deep, nutrient-rich waters to the surface. Those nutrients get incorporated into the fog. The fog rolls in not only bearing moisture but also nitrogen, phosphorus and some minerals. Winds and waves kick the surface high into the air, where it is incorporated into the fog that moves inland.