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Berkeley, CA 94707
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  Nature Elective


The Redwood Forest
First posted February 1, 2004 Last updated June 19, 2009

Cazadero Performing Arts Camp lies nestled along Austin Creek, in a wonderful and rare natural area. The dominant plant is the Coast Redwood, Sequoia sempervirens. This famous symbol of California grows to a height of 200 to 240 feet (the record for a Coast Redwood is 368 feet, taller than either the Statue of Liberty or the Capitol Dome in Washington, DC). The towering size of the Coast Redwood casts a long shadow, both actually and figuratively. Its shade promotes the growth of ferns and cools the streams that flow underneath it. Its leaves and bark contain a reddish toxin, tannic acid, that gives the tree its name and deters other plants from growing. Along with the climate and soil conditions, it defines a plant and animal community called the Redwood Forest. If you have not yet read the Introduction to Biozones, you might want to now, as it will help you understand the rest of this page.

Lets first look at the climate conditions that make the beauty of Cazadero possible.

Climate Conditions
   

At the simplest level, fog is caused by global weather patterns and local hot air rising in the Central Valley pulling in cool ocean air laden with moisture. But the real story is much more interesting.

The story begins with the weather pattern out over the Pacific Ocean. The prevailing winds of the North Pacific High circle clockwise, owing to the Earth's rotation. This effects both the air mass and the ocean surface. As the moist, cool ocean air merges with air masses over the California land mass, it gives birth to a "ballet of fantastic flowing forms of aerial moisture" (SF Chronicle, June 12, 2000).

 

Look at the photograph of California at left, taken from space. The clear skies are caused by a high pressure area off the coast called the North Pacific High, which is a massive, semi-permanent high-pressure system that occupies most of the Pacific Ocean north of the equator. The photo also shows California's 500-mile-long Central Valley. The sun beats down on the Valley, heating the air to temperatures of 100 degress and more. This creates an onshore flow of cool, moist air.

On the right, air from out over the ocean north of California has run into cold water upwelling along the coast, which was caused by the Earth's rotation moving the warm surface water offshore. The combination of cool moist air and cold ocean water has created fog. The waves in the air mass are clearly seen. The mass flows along the coast and into the low parts of the coastal mountains: the river valley of the Russian River and the Golden Gate. You may have seen the ballet of fog as it flows over the Marin Headlands and crosses the Golden Gate Bridge. If you looked closely, you might have been able to see the waveforms of the fog. You certainly can see if it you are flying out of or into San Francisco Airport. (For a more complete analysis of the complex forces that cause our celebrated fog, see The Fog is Clearing.)


Fog rolling in from the ocean over the coast at Mt Tamalpais State Park
Photo taken by David Nelson, July 31, 2004

The fog rolls many summer evenings and persists to around noon. This keeps the temperature down and the humidity up, creating the unique conditions that allow us to have the only population of coast redwoods in the world. In the distance, you can see the fog out over the ocean. Moist, cool air is both drawn in by the updrafts of warm air in the Central Valley as well as pushed in by the North Pacific High (see above). This combines with the upwelling of cold water along the California coast, refrigerating the moist air and condensing its moisture into fog.

Fog rolling in from the ocean along the Russian River
Photo taken by David Nelson, July 23, 2004

This fog is coming in the Russian River basin at 5 pm. The movement of the fog is a fascinating study of the fluid nature of the atmosphere. We often don't think of air as a fluid, a term we usually reserve for liquids. The fog is a great demonstration of the fluid nature of the air. You can see it flow in from the sea, rounding over mountains and descending into valleys and basins. It is easily seen when driving from Marin to San Francisco. As you pass the Marin Headlands and before you cross the Golden Gate Bridge, you can see the fog flowing over the Headlands and out into the bay. This cool flow of moist air is found all along the coast, from Monterey to southern Orgeon, and is essential to the survival of our redwoods.

The Redwood Forest Biozone

Classically, the redwood forest biozone is divided into three forms, and then further subdivided into plant communities. The three forms of redwood forest are the alluvial-flat forest, the redwood/Douglas-fir forest, and the redwood/mixed evergreen forest.

The main area of Camp Cazadero is an example of the first type, the alluvial-flat forest. It is characterized by deep soil that has been deposited by the river over geologic ages. This form of redwood forest provides the ideal growing conditions for redwood trees, and all of the groves of massive coast redwood grow in alluvial-flats. Daily temperatures are mild and seasonal changes are minimal, summer fogs are persistent, soils are deep, well-drained, and nutrient-rich, soil moisture is plentiful, even at the end of California's Mediterranean climate summer (characterized by no rain), and fires are less common and generally of low intensity. The best examples of the alluvial-flat redwood forest are those along the Smith, Klamath, and Eel rivers, but we also have some in the deeper canyons along the San Lorenzo and Big Sur rivers. It is not surprising that all of our famous coast redwood parks are in these areas (see this website for more information about parks: California Recreation). Big Basin State Park, the world's first redwood park (1901), is along the San Lorenzo river.

Notice in the photograph at the right that there are essentially no trees other than redwoods, and that these are all rather tall, with little in the way of understory. This is a classic alluvial-flat redwood forest.

 
Redwoods at Cazadero near the Family Camp
This group of redwoods is located near the Family Camp, just uphill from the upper photograph. This shows the limited understory, with just a few trees filling in the space from the treetops of the redwoods to the ground. It also shows that there are limited groundstory plants: some ferns and shrubs. Although there is glaring sunlight at the top of the forest, very little light reaches the ground. A few sunbeams and sunflecks are all that are available to supply the groundstory plants, so they are few in number and have to be very efficient in using sunlight.
Redwoods at Cazadero near the Family Camp
 

There is a lot to enjoy and to learn about the Redwood Forest. Take a walk around camp and keep your eyes open!

Riparian Biozone

Oak Woodland Biozone

Chaparral Biozone

Grassland Biozone

Trees and Capillary Action

The Age of Redwood Trees

A poem to contemplate while admiring the redwoods: Frost's The Road Not Taken.