Earth & Sky

Our thanks to the following individuals and institutions who assisted in the preparation of this script:

Tom Henry
Giant Sequoia Specialist
Sequoia National Forest
Porterville, CA

The following books, articles and web sites were used in preparing this script:

Worlds Largest Tree is Younger Than Once Thought (US Geological Survey Press Release, December 7 ’00)

Giant Sequoias: Treasures of the Nation (USDA Forest Service Pacific Southwest Region)

Big Tree Life Cycle (excerpted from “The Enduring Giants” by Joseph H. Engbeck Jr., published by the California State Parks. )

Giant Sequoia (Sequoiadendron giganteum) Species Account by Kristine J. Waldorf & Sandra Klepadlos Forest Ecology Page California State University, Department of Biology

Andrew Ellicott Douglass and the Big Trees American Scientist, September-October 2000 by Donald J. McGraw

The Giant Sequoia – Forest Masterpiece (National Park Service Page)

“California’s “Redwood” Trees: Giant Sequoia and Coast Redwood”:http://www.nps.gov/redw/sequoias.htm (National Park Service Page)

Chief Sequoyah (PowerSource.com)

USDA Fact Sheet, Giant Sequoia National Monument

Clinton sets aside sequoia tract – Sunday, April 16, 2000, Associated Press

Author’s Notes:

Not only do giant sequoias grow big, they grow fast. Since tIn the past 40 years, General Sherman’s diameter has increased by 3 inches, that’s equivalent to 40 cubic feet of wood each year!

More Information on the Giant Sequoia (Sequoiadendron giganteum)
by Shireen Gonzaga

Giant sequoias, named in honor of Sequoyah, a Cherokee Indian Chief who invented the Cherokee alphabet, are among the largest organisms in the world – mature trees average about 250 feet high, with trunks about 15 feet in diameter. One notable tree, the General Sherman, is considered the largest living tree by volume in the world, holding about 52,508 cubic feet of wood, It is 275 feet tall, has a circumference at the ground of 102 feet (a base diameter of 36.5 feet), and is believed to be about 2,500 years old.

Along with other redwoods, giant sequoias belong to the Taxodiaceae family of trees. Taxodiaceae originated during the Triassic, about 200 million years ago, and were once abundant throughout the northern hemisphere. In recent geological history, as the climate grew colder, many of these trees retreated south, and some became extinct. The giant sequoia itself has been around for 15 to 18 million years, and once occurred over a larger range when the climate was warmer. Today, they are found growing and reproducing naturally only in one area: the western slopes of the Sierra Nevada mountains.

The natural range of the giant sequoia is restricted to a 260 mile-long area of the Sierra Nevada, at elevations ranging from 4,500 feet to 8,400 feet. The trees are found scattered in forest communities of trees and shrubs, the composition of the forest fauna varying with elevation and latitude. Trees found growing alongside the giant sequoias include sugar and ponderosa pine, white fir, incense cedar, as well as red fir in higher elevations. Giant sequoias are said to occur in “groves,” a gathering of trees in an area. In their range, there are about 75 groves of these giant trees, most of them occurring towards the south of their range.

In the mid-1800s, many giant sequoias were cut down for lumber. Almost one-third of all giant sequoias were felled before they came under protection between 1890 and the 1940s. Today, all giant sequoias are protected from becoming timber. They are mostly under the care of government agencies, and subject to different management approaches: the Bureau of Land Management is responsible for one grove; the National Park Service, about 35 groves; the Forest Service, 38 groves; the State of California manages several groves, and the University of California at Berkeley owns and manages one large grove. Several groves are owned by Native American tribes and by private owners. On April 15, 2000, President Clinton signed a proclamation creating the 328,000-acre Giant Sequoia National Monument, to protect 34 groves of giant sequoia. Although the giant trees themselves are already protected, this new national monument will eventually prohibit commercial timber operations of other tree species that could potentially disrupt the well-being of the giant sequoias.

No one really knows how long a giant sequoia can live. Many of the trees at the Sequoia National Park are believed to be more than 3,000 years old. The oldest known tree to be aged from its tree rings was 3,300 years old when it was felled. The giant sequoia’s long lifespan can be attributed to several of its unique characteristics: it has a thick fire-resistant bark, its wood contains a natural preservative, and the tree is very resistant to damage by insects.

Fire is an important part of giant sequoia forest ecology. Giant sequoias have a spongy fire-resistant tree bark that is 1 to 2 feet thick, allowing them to withstand forest fires. Fire is also important for the reproduction of these trees. Most seeds are released after a fire and need bare mineral soil, cleared by fire, to germinate. Young seedlings need sunlight during their initial growth stages, and will wither away under the shade of understory trees and shrubs. However, the benefits of forest fires were not recognized during early forest management practices. Fires were commonly extinguished, allowing the growth of smaller trees and shrubs that would otherwise be naturally removed by fire to flourish. In the 1950s and 1960s, the benefits of fires in sequoia groves became increasingly recognized as scientists realized that the overgrowth of the forest understory had resulted in a steep decrease in giant sequoia reproduction.

Currently, giant sequoia groves are managed differently by the various agencies that are responsible for them. According to Tom Henry, a giant sequoia specialist at the U.S. Forest Service’s Sequoia National Forest, “to a very large degree, all wildfires (man-caused or natural) on our forest (and hence in the Monument) are aggressively suppressed. The only exception to this suppression policy is: There are a very few small groves in designated wilderness on the forest. If a fire is in the wilderness, these fires may be under a “wait-and-watch” approach if the Forest has an approved management plan for that particular wilderness.”

Yet giant sequoia tree regeneration is on the decline. Said Henry, “Until a management plan for the newly-established Giant Sequoia National Monument is complete, no active management is currently being taken in any [Forest Service] groves other than suppression of fires if they occur. We have planted many young seedlings in the past, and in the 1980s, some limited harvesting [of other tree species] in groves led to very successful young regeneration. Since that time, though, no active management has taken place. Other agencies such as the Park Service and California Department of Forestry and Fire Protection continue to actively manage their groves in different ways, leading to some successful regeneration.”

Giant sequoia seeds come from egg-shaped cones that grow up to three inches long, with each cone containing about 200 seeds. These seeds are so small that 3,000 seeds weigh only one ounce. The cones take two years to mature, and can remain on the tree for as long as 20 years. A giant sequoia produces about 1,500 cones each year, and could have as many as 40,000 cones at any given time, though about one-third of those cones are dry and seedless. Most seed releases occur as a result of forest fires: intense heat from the fires cause the cones to dry and open up, releasing the seeds. Some seeds, not much though, are released by the larvae of long horned beetles that bore into the fleshy part of the cone, releasing some seeds, as well as by the Douglas squirrels that feed on cones.

Even though giant sequoias produce prodigious amounts of seed, only a very small fraction of the seeds will germinate. The seeds need very specific growing conditions; they cannot tolerate too much exposure to sun and have to be within one-half inch below the soil surface. They are also very sensitive to soil temperature and moisture during the germination stage. After germination, the seedlings need sunlight and will wither under the shade of an overgrown forest understory.

During the first two years of life, the young giant sequoia tree is extremely fragile. It is easily destroyed by fire. It must survive the dessicating conditions of dry summers, the cold effects of winter that cause frost damage, soil changes due to freezing moisture, and fungus. In spring, erosion could be a problem for seedlings close to streams. If a young tree can overcome these initial hurdles and become established, it will emerge as a tough little tree that is better equipped to withstand the extremes of the environment.

A young sequoia grows quite rapidly. During its early years, the tree has a conical appearance with a pointy top. But as it matures, its crown becomes more dome-shaped. As the tree ages, older branches closer to the base are naturally pruned away. Many old trees are also “snag-topped,” that is, they have dead wood at the top of the crown. This is mostly caused by fire damage – about 85% of sequoias with snag tops also have burn scars on the trunks.

During the first 50 to 100 years of their lives, giant sequoias can grow about 2 feet in height each year. Its massive trunk however, continues to grow over the lifetime of the tree. Young trees growing in favorable conditions can increase by 1 inch per year in diameter, producing 1/2 inch growth rings. As the trunk becomes larger, the annual growth rings shrink in width, but that doesn’t mean the tree isn’t growing; the tree continues to increase in volume each year but because its diameter is larger, the new wood is spread out over a larger area, therefore appearing as narrower tree rings. The General Sherman tree, the largest tree in the world by volume, may also be the fastest-growing tree in the world. Over the last 40 years, its diameter has increased by 3 inches. Considering that the tree is 272 feet high and 30 feet in diameter, General Sherman has been generating 40 cubic feet of new wood each year, for the past 40 years!

The root system of the giant sequoia is as impressive as the tree, but most of us don’t see that intricate network. Most of the roots are tiny threadlike feeders that extend from a network of larger roots, tiny structures that absorb moisture and nutrients from the soil. The roots of a large giant sequoia spread out about 100 to 150 feet, in some instances 200 feet, around the tree. However, most of the root system does not extend more than 4 to 5 feet below the soil surface, a surprisingly shallow root structure for such massive trees that tower as high as 250 to 300 feet.

Giant Sequoias and Dendrochronology

Dendrochronology, the dating and study of annual tree rings, was created by astronomer Andrew Ellicott Douglas in the early 1920s. He worked on the hypothesis that the width of tree rings, layers of growth that are laid down each year in a tree’s trunk, are directly related to the tree’s food supply, which indicates the amount of water that is available. Therefore, tree rings can provide a natural documentation of the climate at that tree’s locality.

One important aspect of tree-ring dating, developed by Douglas, was called cross-dating. Each cross-section of a tree has a signature ring pattern that corresponds to the climatological conditions during that tree’s lifetime. He used tree-ring specimens from dead and living trees of a particular area, with lifetimes that overlapped in time, from a point in the past to the present. He was able to match overlapping tree-ring signatures from various time intervals in different trees to build a continuous chronology of the climate from a particular time in the past to the present.

Douglas first started working with ponderosa pine tree rings in Arizona, but later switched to the giant sequoia. In a book published in 1919, he demonstrated the value of giant sequoias in developing this new field of dendrochronology: giant sequoias were long-lived trees that offered a long chronology of rings within one tree. He also pointed out that the location of a study tree was a critical factor in getting good data. Trees in “water stressed” areas, that is, trees growing in well-drained areas that got their moisture only from climatic sources like rain and fog, offered a good record of climatic conditions in the rings. However, trees that obtained moisture from streams or other natural sources of ground moisture, had rings that were not indicative of climatic conditions.

Dendrochronology was first applied to dating the ruins of ancient Anasazi Indians in the four corners region (where Arizona, New Mexico, Utah, and Colorado meet). At first, he hoped to use the giant sequoia for this task, but this was not possible because of the climatic differences between the site of the ruins and the sequoia forests of northern California. He therefore turned to local trees near the site of the ruins, and built a long chronology of tree rings. He was then able to match tree ring patterns in his chronology with wood that came from roof beams of the Anasazi dwellings, and date the ruins.

Douglas spent much of his career continuing to work on giant sequoias. The oldest tree he was able to date reached back to 1305 B.C.. When he first started working on tree rings, Douglas was interested in looking for a correlation between climatic changes and the 11-year sunspot cycle. As hard as he looked for evidence of sunspot-induced climate changes, it was not to be found in the tree rings of the giant sequoias, by him or by others who continued his quest.