San Francisco State University
Geography 316: Biogeography
The Biogeography of Sequoia sempervirens
By Brandon Jebens, student in Geography
316, Fall 1999
Species: Sequoia sempervirens
by Ed Cooper, Redwood Empire
Description of Species
Redwoods are the tallest trees in the world. These are not just individual trees growing in favorable conditions, but as an entire species, they are the tallest in the world (Snyder 1992). On average, the trees grow up to 280-325 feet in height, with a trunk 8-15 feet in diameter, and the tallest reaching heights over 360 feet (McBride and Jacobs 1977, Snyder 1992). These giant trees tend to be scattered throughout the entire range rather than clumped in one particular area (Snyder 1992).
Redwood bark is fibrous, thick, and furrowed with long, vertical ridges. It is reddish brown in color, but can weather to a dull gray. The wood is tough, but light and soft (Snyder 1992). The heartwood is red and is believed to be the origin of the name "redwood" (Snyder 1992). There are two kinds of leaves: a small awl shaped variety that grows close to the stem on exposed branches, and a long, needle like variety in two rows on the rest of the branches. Both are green in color. Redwoods are evergreen, and do not lose their leaves like other members of the Taxodiaceae family (Snyder 1992).
The roots are incredibly shallow for such a huge tree. Roots may only penetrate 6 feet below the ground (Snyder 1992). Redwoods have no taproots (Fritz 1995). The roots also have an amazing ability to adapt to burial by growing new roots on top of the old. When a tree is inundated with silt from flooding, and the roots are buried under more soil, the tree simply stops growing the buried roots and begins a newer and higher set on top of the old in response (Fritz 1995). Because of this, upturned redwoods often look like they had deeper roots than they actually did.
Redwoods are also extremely long-lived trees. They may reach ages of 2200 years, though, as with height, these extremes are rare (Snyder 1992). Much more common are trees that are 600-800 years of age (Snyder 1992).
Photo by David Swanlund, Redwood Empire
Redwood forests have the highest biomass of any terrestrial ecosystem in the world, more than 8 times the total above ground biomass of a tropical rainforest (Snyder 1992). Common averages of board feet per acre range from 125,000 to 150,000, and the record from a single tree comes from Humboldt County at 480,000 board feet of prime, first class lumber, or enough to build 22 5-room houses (Snyder 1992).
Natural elements such as fire and fog play integral roles in the redwood community, and redwood adaptation to these elements make them unique trees in many ways. Their methods of reproduction are also worthy of note, again because of the exceptional attributes they have.
Redwoods reproduce two ways. One is by seed growth, just as most plants, and the other is by sprout (McBride and Jacobs 1977, Snyder 1992). Redwoods are unique among conifers in their ability to vigorously sprout (Snyder 1992). Sprouts come from a collar at the base of the tree made of dormant bud material, but are usually inhibited to grow due to the constant flow of a growth regulating hormone released by the tree (Snyder 1992). When the tree undergoes stress, the flow is interrupted and a sprout begins to grow (Snyder 1992). Should the sprout survive, it may eventually grow into a full-grown tree. When one tree produces many of these sprouts and a number of them survive, it's not uncommon for them to form a ring around the original tree and produce what is commonly called a "family circle" or "fairy ring" (McBride and Jacobs 1977, Snyder 1992). The original tree may pass away, yet leave its descendants behind in the family circle. These trees are all related to each other because they came from the original tree, and that is why they are called a "family circle." These family circles are easily seen in most redwood forests.
Redwoods do reproduce by seeds, though the seeds and cones are smaller than one would anticipate from such a large tree. Redwood cones are about the size of an olive or grape, and contain between 60-120 seeds (Snyder 1992). The seeds, small and light, would take 59,000 to 300,000 to make one pound (Snyder 1992). Redwoods produce both male and female flowers on the same tree, but separate branches (Snyder 1992). Trees begin to bear seeds between the ages of 5-15, and maximum production usually occurs between 60-250 years (Snyder 1992). The flowering season usually runs from mid-October to late March (McBride and Jacobs 1977, Snyder 1992). Most seeds begin to germinate once they land on fertile soil. (Snyder 1992)
Once redwoods are established, they have amazing characteristics that help them survive and adapt to their environment. Redwoods contain a chemical in them called tannin that helps protect them from fire, insects and fungus (Monroe 1999). Redwoods also contain no resin (McBride and Jacobs 1977, Snyder 1992) and their thick bark may grow up to 1 foot thick (Snyder 1992). This bark helps to protect the tree from fire damage (Monroe 1999). Fire is a natural part of the redwood ecosystem and has amazing benefits for the forest environment. Fire happened naturally every 22-27 years in some redwood communities (Jacobs et al. 1985, Greenlee and Langenheim 1990). Benefits of fire ecology in a redwood forest include aiding nutrient recycling, clearing the understory, controlling forest insects and diseases, and preparing the soil for seeds (Monroe 1999). Suppressing fires has shown to create vulnerability in redwoods to disease and catastrophic large fires (Monroe 1999).
Photo by Ed Cooper, Redwood Empire
Another adaptation redwoods have in response to their natural environment is in regards to fog. Fog is a fact of life for coastal California plant communities, and even the mighty redwood has shown not only a tolerance but a dependence on it. Fog can define limits of redwood groves, but fog also plays a key role in water use by the redwoods. Fog use by redwoods is high (Dawson 1998). Because the California summers are dry and have no rain, the moisture from the summer fog is in high demand and trees can use up to 600 liters/day (Dawson 1998). Redwood foliage is actually very efficient at "stripping" fog moisture from the air and making it available for the ecosystem (Dawson 1998). Dawson (1998) also notes that during the summer months, redwoods may get up to 40% of their water from fog, and that fog can account for 13-45% of its water uptake annually. Besides water intake, redwoods receive many valuable benefits from fog. Fog can "wash" dust and other accumulated matter on redwood leaves to the ground and add the nutrients contained there to the soil (Azevedo and Morgan 1974, Dawson 1998). Dawson (1998) noted that there is more fog accumulation in the ecosystem in areas with large, mature redwood trees as opposed to more open, less forested areas and concluded that deforestation will also cause a reduction in moisture inputs and therefore nutrient inputs, nutrient cycling and decomposition. Redwoods, therefore, not only rely on fog, but the redwood ecosystem also relies on the redwoods.
The earliest known Sequoia (S. jeholensis) comes from the Jurassic, and is known only from fossil leafy imprints (Miller 1977). These closely resemble the modern S. sempervirens and may be an early relative. There is no consensus as to the location of the origin of the Sequoia's, but is believed to be either the arctic islands or west-central North America (Snyder 1992). The fossil record is not clear. By the end of the Cretaceous, 65 million years ago, however, S. sempervirens is known to have existed and been fairly widespread (Snyder 1992).
S. sempervirens belongs to the Taxodiaceae, or deciduous cypress, family, which has 15 species, distributed among 10 genera. None of the species are found on more than one continent, which has lead Miller (1977) to conclude that they are all modern representatives of "long lines of specialization," and may be relicts of more abundant groups in the past (p. 250). Though the coast redwood and the giant sequoia (Sequoiadendron giganteum) are closest geographically, it is believed that the coast and dawn redwood (Metasequoia glyptostroboides), found in China, are closer genetically (Snyder 1992).
The oldest known member of the sequoia family is from the Late Jurassic Southern Manchuria, and by the end of the Mesozoic all northern continents had representatives of sequoia species alive today (Snyder 1992). Seqouia sempervirens had reached its northernmost limits during the Paleocene and Eocene, 65 MYA to 38 MYA. It is known to have been on the islands of Svalbard, today part of Norway and well above the Arctic Circle (Snyder 1992). During the Oligocene and Miocene, 38 MYA to 6 MYA, its range had moved south due to cooler and drier climates, and by the Pliocene it had become established in its present location. At this time, it had also disappeared completely from Europe and Asia (Snyder 1992).
Map from Snyder 1992
The present distribution of Sequoia sempervirens is along a narrow strip of land hugging the Pacific Coast of the United States. It reaches from the southernmost tip of Monterey County in California, and follows a discontinuous line all the way up to the Oregon border. In fact, Sequoia sempervirens misses out on being an exclusively Californian tree by 14 miles over the Oregon border. On average, the tree is not found more than 20 miles inland, but its furthest inland distribution is roughly 40 miles in Napa County where the climate is still moderated by marine influences. This narrow strip of land is about 500 miles long, and originally contained approximately million acres of old-growth, virgin forest.
Limiting factors that define redwood distribution are generally climatic, but are also geologic. Sequoia sempervirens does not tolerate extreme conditions of either temperature or precipitation. On average, the temperature of the redwood forest ranges between 47 degrees Fahrenheit in January to 64 degrees in July (McBride and Jacobs, 1977). Temperatures rarely exceed freezing or reach above 100. Precipitation is between 35 - 90" annually with larger amounts of precipitation the further north you go. As it is located in the Mediterranean climatic biome, the redwoods receive the majority of their precipitation in the winter. Further north of the current redwood distribution provides too cold and too wet a climate for successful colonization, and further south the climate is too hot and dry for the trees.
The summer fog is generally recognized as a limiting (and contributing) factor for redwood distribution, but as McBride and Jacobs (1977) point out, the correlation is not perfect. The fog belt extends way beyond the distribution of the redwoods, reaching down to Baja California and up to Portland, Oregon. There are several severe gaps in the redwood distribution that cannot be attributable to the fog as well (McBride and Jacobs 1977). Fog, because it occurs primarily in the summertime, does play an important role for some redwoods. In the southern range of their geography, the fog may be the key factor in keeping redwoods alive. The heat and dryness in the south confines redwoods to canyons and river valleys, where summer fog brings much needed and valued moisture.
In general, redwoods are confined to soils of serpentine origin (Monroe 1999). Serpentine is a metamorphic rock that began as bits of the earth's mantle. As it weathers, it provides a soil too harsh for some plants, but is ideal for redwoods.
Barnett (1998) notes that the change of redwood distribution over the past has come from the relationship the tree has with its roots. Or rather, with a symbiotic fungal association found in the roots. This fungus allows the tree to absorb certain nutrients from the soil (Barnett 1998). This type of mycorrhizal, or fungal, association is found in other trees as well, but in redwoods the fungus penetrates the tissues of the roots (Barnett 1998). At the furthest redwood expansion, this fungal association allowed the roots to absorb the nutrients it needed in the high latitude locations. Then, when global climate changed 20 million years ago, redwood distribution began to shrink gradually to its present location. Barnett notes that the fungal association was no longer capable of removing the necessary nutrients from the soil because the soil changed as the climate changed. Plants and trees, such as pines, which have fungal associations that are more superficial and do not penetrate the tissues as deeply were better able to survive the climates and eventually helped push out the redwoods (Barnett 1998). He notes that the distributional success of the redwoods has partly depended upon the fungal associations it has formed.
Other interesting issues
The Coastal Redwood can be seen in many good National and California State parks. Below is a list of some parks with more than 1,000 acres of old-growth forest. There are many other good parks besides these.
|Name of Park||Old-Growth Acreage|
|Big Basin Redwoods State Park||2,000|
|Butano State Park||1,500|
|Del Norte Coast Redwoods State Park||2,600|
|Humboldt Redwoods State Park and Holbrook-Whittemore Groves||20,333|
|Jedediah Smith Redwoods State Park||9,450|
|Portola State Park||1,400|
|Prairie Creek Redwoods State Park||8,240|
|Redwood National Park||19,650|
Table from Snyder 1992
Interesting Web Links
Azevedo, T.E. and D.L. Morgan. 1974. "Fog Precipitation in Coastal
California Forests." Ecology. 55:1135-1141
Barnett, A. 1998. "How the North was Won." New Scientist. 158 (2139): 34-37
Collings, R. 1985. Redwood Empire. Anaheim, CA: Adam Randolph Collings , Inc.
Dawson, T.E. 1998. "Fog in the California redwood forest: ecosystem inputs and use by plants." Oecologia. 117: 476-485
Fritz, E. 1995 (49th printing). Story Told By A Fallen Redwood. San Francisco, CA: Save-The-Redwoods-League
Greenlee, J.M. and Jean H. Langenheim. 1990. "Historic Fire Regimes and their Relation to Vegetation Patterns in the Monterey Bay Area of California." American Midland Naturalist. 124 (2): 239-253
Jacobs, D. F., D.W. Cole, and J. McBride. 1985. "Fire History and Perpetuation of Natural Coast Redwood Ecosystems." Journal of Forestry. 83 (6): 494-497
McBride, J. and D. Jacobs. 1977. Ecology of Redwood and the Impacts of Man's Use of the Redwood Forest as a Site for Recreational Activities-A Literature Review. Muir Woods Research Project, Technical Report No. 1. Department of Forestry and Conservation, University of California, Berkeley. Prepared for USNPS. Contract No. CX 8000-6-0035
Miller, C.N. 1977. "Mesozoic Conifers." Botanical Review. 43 (2): 217-280
Monroe, Mia. August, 1999. Personal Interview. Site Supervisor, Muir Woods National Monument
Snyder, J. A. 1992. The Ecology of Sequoia sempervirens: An Addendum to "On the Edge: Nature's Last Stand for Coast Redwoods". M.A. Thesis, Department of Biological Sciences: San Jose State University
Veirs, S. 1989. Redwood Relatives. Muir Woods National Monument
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