thank fog for redwoods

by Kyle Pinjuv

​Fog: Some embrace the cool reprieve it offers from hot summer temperatures. Some feel betrayed by its presence as they approach the beach in shorts and a tank-top with summery intent only to be forced to spend the day wrapped in a towel shivering in a cloud. Fog limits your vision and inspires the creative mind. It reduces contrast during movement, changing our perception of reality and literally causing us to move differently through space. It moves border-free without discrimination over land and sea. We cannot own it or control it. The fog is the San Francisco Bay Area’s breath. It is the gift that allows our iconic redwood forests to flourish. It is itself a coastal icon.

​Fog along the coastal belt is a result of our region’s unique geography, ocean currents, wind and air temperature both inland and offshore. It all begins as the spring sun warms the Central Valley of California: The heated air rises creating a low pressure system along the ground in the Valley, while at the same time, warm air moves north from the equator over the cool Pacific Ocean creating a high pressure system. The high pressure is then pulled inland toward the low pressure, balancing the two systems. While this balancing act is occurring, wind from the northwest, full of moisture gathered while traveling over thousands of ocean miles, comes into contact with the cold upwelled waters off the California coastline. The air is cooled, causing moisture to form into visible droplets. Eventually, the accumulation of billions of these drops occurs and produces what we call fog. The fog is pulled with the balancing high and low pressure systems from the coast as far inland as the Central Valley.

This complex process of fog formation is part of a larger ecological process that allows our beloved coastal redwood habitats to thrive. Summer is the growing season for coastal redwoods and they rely on the cool, moisturized air to collect water in an otherwise dry season. Approximately 30–40 percent of the water supply used by redwoods comes from fog. With the trees’ great height, they rely on pulling moisture both from the ground and from the air. Redwoods are one of only a few tree species that can move water in both directions. The fog also contributes to the greater coastal redwood ecosystem by soaking the ground up to 35 centimeters deep!
 
There have been studies throughout Northern California looking at how climate change reduces the differential of air and ocean temperatures resulting in the decrease of total days of fog per year. Without the fog, coastal redwoods are more vulnerable to drought and die back at the tops of the trees. With the drying of soils and hot summer temperatures, redwood seedlings are especially susceptible to drought conditions. Many organizations and agencies will be keeping a close eye on fog reduction as it has the ability to greatly impact our coastal ecosystems.
 
We are so often grateful for the landscapes of Sonoma County — and rightfully so — but every so often it is important to take a broader view of why this region’s land is so special. Many times, the outside forces that know no political boundaries, such as the wind, rain and fog, allow this region to flourish. It is our duty as stewards of the land to not only protect that which can be bought and sold, but also to care for our seas and our air. Take away the health of our shared planetary resources and we are left with little to protect. 

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Kyle Pinjuv is the stewardship associate project manager at Sonoma Land Trust.

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