Coast Redwood Germination and Growth

Three Redwood Relatives

The Coast Redwood has only two close relatives, the Giant Sequoia and Dawn Redwood. Although the Coast Redwood has been cultivated elsewhere, this tree naturally achieves its majestic heights and lush groves only in one place in the world -- a 450-mile strip along the Pacific Coast of North America. The trees prosper in this mild climate zone, where winter rains and summer fog provide an even temperature and a high level of year-round moisture.  

Redwoods are a hydrostatic marvel. They can siphon water upward to great heights, fighting gravity and friction every inch of the way. And during the dry summers in California, the coast redwoods actually create their own "rain" by condensing heavy fog into drenching showers that provide welcome moisture to the roots below.

In addition, scientists believe that redwoods take in much of their water directly from the air, through their needles and through canopy roots which the trees sprout on their branches. Lofty "soil mats" formed by trapped dust, needles, seeds and other materials act like sponges to capture the water that nurtures these canopy roots. Moisture from fog is thought to provide 30% to 40% of a redwood's water supply. 

Young redwoods use sunlight so efficiently (3-4 times more than pines) that they can grow even in deep shade. But with full sunlight and moist soil, a redwood sapling can grow more than 6 feet in a single growing season!

The coast redwoods are the tallest living species on Earth. Often they can reach heights of 300-350 feet and diameters of 16-18 feet. More than a dozen trees exceeding 360 feet in height are now growing along the California coast.

The redwood's thick bark, with deep furrows running the length of the trees, is a rich reddish brown. It is this bark that gives the redwoods their excellent fire-resistant quality. 

Coast Redwood Needles

The dark green leaves are needle-like and grow flat off the branches. Small cones, usually about an inch long, hang from the branch tips.

Redwood Seeds

Redwood cones release tiny brown seeds when mature. (They're so small that it takes about 125,000 to make a pound!) A single tree may produce six million seeds in a year. Of these seeds, less than 5% germinate, and of these, very few actually grow into seedlings. Redwoods are also capable of sprouting from the roots of parent trees, from dormant buds in the burls at the base of a tree, or from fallen trees. As well, if a tree is cut or burned, a family circle of trees ("fairy ring") may sprout up from the stump. These sprouts, because of already established root systems, grow more vigorously than seedlings and so are the more common form of reproduction. In fact, successive generations of sprouts are really "clone trees". Thus the genetic information of an individual redwood may be thousands of years old, dating back to the first parent. Will grow in USDA zones 7-10.

The Importance of the Summer Fog on Coastal Redwoods

According to Steve Norman of the United States Forest Service, climate change in coast redwood forests do affect its growth and ecosystem. He points out that despite being buffered by a cool humid coastal climate, future changes in climate may affect the coast redwood forest in direct and indirect ways. So, one of the most important climate-related factors that influences fire risk and the floral and faunal character of the coast redwoods is the incidence of summer fog. For those of us who have had the pleasure of living in Northern California and along the coast, the summer fog is a common occurrence. Some sites receive a great influx of moisture during the otherwise dry summer from fog drip, but the cooler temperatures and reduced evapotranspiration along the overcast coast are probably a more widespread and influence on fire regimes.

The interesting relationship between fog-stratus and regional temperature is known to those who have lived on the redwood coast for any length of time. Any occurrence of summer fog and cooler temperatures indicate to those who live to the east of the Trinities (such as in Redding) that the summer heat will be at your doorstep. Along the coast, cool water up-wells offshore as the California current flows southward. Warmer air moving over this humid surface is chilled and condenses. When interior temperatures rise, this marine layer of air is pulled inland and gets forced against the coastal mountains and is vertically contained under an inversion associated regional high pressure. Given this persistance of this pattern during most year's fire season, the local occurrence probability of fog-stratus helps define the fire hazard as well as the vegetation that is found there.

The incidence of coastal fog-stratus varies over time. Less fog was recorded during the fire seasons during the 1920s and 1930s and 1950s, while fog was common during the 1890s, 1910s, 1940s and 1970s. It is common to observe the strongest fire activity in the interior Klamath mountains on days when this coastal fog-stratus pattern is best developed. Variation in fog-stratus over centuries can alter the fire occurrence probabilities which affect the importance of seeding trees, such as Douglas fir and patterns of biodiversity.

Ongoing research models the incidence of fog-stratus in relation to historical fire activity and vegetation. This knowledge will help managers understand the specific climatic mechanisms that create patterns of fire hazards and how fire-related risks might change over time. The 2008 fire season was extraordinary in northern California. From space, the ancient relationship between coastal fog that ameliorates the fire hazard, and interior burning, indicated here by grey smoke, is well illustrated (below; The top of the image is near the Oregon-California border, Lake Tahoe is in the right center and Monterey is at bottom center). Note the pattern of where coastal fog usually occurs. The incidence of fog in northwestern California (upper left) is more interior than along the Mendocino coast (center). These mid-day images under-represent the influence of early morning fog, which also contributes to higher fuel moistures and vegetation pattern.