Low cloud surrounding a tree covered mountain on an overcast day.

Fog sipping coastal redwoods – World Geographer

Fog is frequently found along coastal areas of parts of Northern California. California’s coastal ecosystems have evolved to take advantage of this regular flow of moisture-saturated air in a region with a distinct dry season during the late spring through late fall months.

One such ecosystem is the coastal redwood forests of Northern California. These areas are dominated by coastal redwood trees (Sequoia sempervirens), a type of evergreen tree native to the west coast of North America. Coastal redwoods extend along a narrow strip near the coast from the southern region of Oregon down to the central California region.

Coastal redwood forests are limited to the extent that coastal climate can reach inland. Therefore, most Coastal redwoods are found up to 50 miles off the Pacific coast Moderate climates and constant fog during the drier summer months provide the conditions in which these trees thrive.

Coastal redwoods thrive in areas where fog and moisture-laden clouds persist during Northern California’s drier summer months. Fog and clouds roll into the Santa Cruz Mountains during May. Photo: Caitlin Dempsey.

There are only a very limited number of old-growth redwoods left

Most of the redwoods growing today are second growth forests, a direct result of forest logging that began in the mid-1800s in California. According to Save Our Redwoods, only about 5% (110,000 acres) of old-growth native redwood forests Remains. The vast majority of coastal redwood forests are found on private lands (1.2 million acres – 77% of the total range) while about 382,000 acres (23%) of the coastal redwood range is on protected lands.

A pie chart that is mostly yellow to green with small green wedges to show how little of the original ancient redwood forest remains.
A pie chart created by the National Park Service shows how much of the original 2 million acres of historic growth remains.

Multi-layer canopy system

Coastal redwood forests contain a mixture of trees and shrubs that coexist with tall redwood trees. Common tree species in these forests can include Douglas fir, bigleaf maple, California bay laurel, madrone, and tanoak. Common shrubs found in the coastal redwood ecosystem include California hazel and wood rose. Common forest floor plants are redwood sorrel, redwood trillium, sword fern, and bracken fern.

A view of the lower forest canopy and floor in a redwood forest.
Beneath the coastal redwoods, trees and other forest plants thrive. Photo: Caitlin Dempsey, Henry Cowell Redwoods State Park.

“Cathedral Forests”

Coast redwood trees are the most common aspect of a coastal redwood forest. Coastal redwoods are the tallest tree species in the world It can reach a height of 350 feet. The tallest tree in the world is a coastal redwood called Hyperion that grows in Redwood National Park and reaches a height of just over 380 feet (about 116 meters).

Coastal redwoods can grow up to 22-27 feet wide and live 2,000-2,500 years. Fossil records show this The redwood’s relatives grew 160 million years ago during the Jurassic period.

Straight view of a grove of redwoods.
Standing in a grove of redwoods has been described as feeling like you are in a cathedral. Photo: Caitlin Dempsey.

In ancient forests, forests have been described as being like “cathedrals” because of the awe inspired by the enormous height of these trees. The dry, earthy scents from the redwood trees and the quiet rustle of the trees create ideal conditions for forest bathing by visitors.

Albino coastal redwood

One rare species within the coastal redwood forest is the white coastal redwood. These white-leaved redwoods are known by a variety of nicknames, most commonly as “ghost trees” or “ghost redwoods.” These trees are so rare, one researcher estimated in 2016 that there were fewer than 406 of them.

A small redwood sapling with white needles grows in the forest.
An albino redwood tree in Henry Cowell Redwoods State Park. Photo: Caitlin Dempsey.

The white color of white redwood trees is the result of a genetic mutation that prevents the tree from using photosynthesis to produce chlorophyll, the pigment that makes plants green. To survive, whitewashed redwood trees pull sugars from their natural host redwood trees through interconnected root systems because they are unable to make their own food from sunlight.

One researcher, Zane Moore, hypothesized that these whitewashed redwood trees have a symbiotic relationship with their host plants. Moore found that Edwood albino trees contain higher concentrations of heavy metals than their green counterpartsThis is thought to be due to poor stomatal control by albino plants. Moore hypothesized that albino plants act as a reservoir for cadmium, copper, and nickel in exchange for sugars from healthy redwood trees.

Fire-adapted ecosystem

Coastal redwood trees have remarkable adaptations that enable them to survive and even thrive in fire-prone environments. Its thick bark, rich in tannins, provides resistance against low-intensity fires and acts as a protective layer.

Redwood trees with buds growing from the base of trees in the forest.
Basal sprouting, a form of vegetative regeneration, enables coastal redwood trees to recover quickly from wildfires and continue their life cycle even after sustaining significant damage. Photo: Caitlin Dempsey.

This species also has the ability to sprout new shoots from the base, known as basal shoots, allowing them to regenerate quickly after fire events. This ability to resist fire has allowed redwoods to be a dominant species in fire-dependent ecosystems. However, their fire resilience is adapted to climate conditions and historical wildfires – that is, fires of low to moderate intensity over relatively long periods, allowing sufficient time for recovery.

A redwood snag burning with fire.
A redwood snag burning with fire. Photo: Caitlin Dempsey.

Climate change is altering the fire regime by creating longer, hotter and drier droughts, stressing and weakening trees, leading to more frequent and intense wildfires that can overwhelm even resilient coastal redwoods. Rising temperatures and changing rainfall patterns are creating drier conditions, making forests more vulnerable to devastating fires. This change poses a major threat to the longevity and health of these ancient trees, thus changing the composition and dynamics of the ecosystems on which they underpin.

The fog sustains the coastal redwood ecosystem

Fog is an important source of water, especially during the drier summer months. Northern California has a Mediterranean climate characterized by cooler, wetter winter months and drier, hotter summer months.

As temperatures rise, the demand for water by plants in this region increases. For plant communities near the Pacific coast, this demand is partly met by the presence of marine-induced fog.

Redwood trees have the ability to capture fog and use it as a source of moisture. Coastal redwood trees capture fog through their needles, a process known as “foliar absorption,” in which moisture is absorbed directly through the leaf surfaces.

View of a tall coastal redwood tree with an overcast sky.
Fog brings water to the coastal redwood forest during the summer months. Photo: Caitlin Dempsey.

Northern California coastal geography and fog formation

In Northern California, summer fog formation near coastal areas is primarily influenced by the interaction between the cool California Current and warmer inland air. Cold ocean water cools the surrounding air, creating a cool, moist marine layer. During the summer, warm air moves from the interior toward the ocean.

Satellite image of the Pacific Coast showing the marine layer along the coast of northern California and Oregon.
The marine layer is an important summer water source for the coastal redwood forest ecosystem. Satellite image of the marine layer over coastal areas of northern California and southern Oregon on September 29, 2006. Image: NASA, Aqua satellite.

When this warmer, less dense air meets the cold marine layer, it causes the moist air to rise until it encounters the temperature inversion layer, which is typically caused by high-pressure systems. This inversion traps moist air, forcing it to cool to the dew point, leading to condensation and fog formation.

Fog provides summer water for forests in coastal redwood forests

Fog is important not only for coastal redwoods, but also for plants with shallow roots that cannot access deeper soil water. Studies have shown this Fog brings a large amount of water to coastal redwood environments. Studies, such as one conducted in 1998, have also shown that 66% of the water presence in belowground plants in coastal redwood forests came from fog water falling from trees into the forest soil.

Declining fog and climate change

As climate change affects local conditions in Northern California, researchers are concerned about impacts on redwood trees and the essential ecosystem that relies on fog for water. Warm air holds less moisture. As summer becomes hotter and drier, this has a negative impact on fog humidity. For example, The National Park Service reports that the fog that redwood trees need to survive in Muir Woods National Monument has decreased by a third..

The coastal redwood forest has evolved over millions of years and fog is an essential ecological component. In these forests, the presence of summer fog affects everything from water availability, plant survival, microclimate and carbon sequestration. As climate change continues to worsen conditions conducive to survival, large segments of California’s forests, including redwoods, are at risk of turning into zombie forests as new generations of these majestic trees are unable to survive.


Azevedo, J., & Morgan, D. L. (1974). Fog falls in California coastal forests. Ecology, 55(5), 1135-1141.

Dawson, T. E. (1998). Fog in a California redwood forest: ecosystem inputs and use by plants. Ecology, 117476-485. https://doi.org/10.1007/s004420050683

Johnston, J. A., and T. E. Dawson. “Climatic context and ecological impacts of reduced summer fog in the coastal redwood region.” Proceedings of the National Academy of Sciences, Vol. 107, no. 10, 2010, pp. 4533-4538., doi:10.1073/pnas.0915062107.



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