Redwoods

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Redwoods

There are three genera of redwood trees, each with a single species . The native range of the coast redwood (Sequoia sempervirens ) is a narrow 450-mi (725-km) strip along the Pacific Ocean from central California to southern Oregon. The giant sequoia (Sequoiadendron giganteum ) is restricted to about 75 groves scattered over a 260-mi (418-km) belt, nowhere more than 15 mi (24 km) wide, extending along the west slope of the Sierra Nevadas in central California. The third species, dawn redwood (Metasequoia glyptostroboides ), was described first from a fossil and was presumed to be extinct. However, in 1946 live trees were discovered in a remote region of China. Since then, seeds have been brought to North America, and this species is now found in many communities as an ornamental planting. Unlike the coast redwoods and giant sequoias, dawn redwoods are deciduous.

Redwoods are named for the color of their heartwood and bark. The thick bark protects the trees from fires which occur naturally throughout their ranges. Their wood has a high tannin content which makes it resistant to fungi and insects, making redwood a particularly desirable building material. This demand for lumber was responsible for most of the destruction of the original redwood forests in North America. In 1918, the Save-the-Redwoods League was formed to save redwoods from destruction and to establish redwood parks. This organization has purchased and protected over 280,000 acres (113,400 ha) of redwood forests and was instrumental in the establishment of the Redwoods National Park . The term Sequoia used in the generic names of these species, and in the common name giant sequoia, honors the Cherokee Chief Sequoyah who developed an alphabet for the Cherokee language.

Coast redwoods

Coast redwoods are the tallest and one of the longest living tree species. Average mature trees are typically 200–240 ft (61–73 m) tall, although some trees exceed 360 ft (109 m). The world's tallest known tree is a coast redwood that stands 368 ft (112 m) tall on the banks of Redwood Creak in Redwood National Park. In some areas coast redwoods can live for more than 2,000 years. They are evergreen, with delicate foliage consisting of narrow needles 0.5–0.75 in (1.3–2 cm) long, growing flat along their stems and forming a feathery spray.

Coast redwoods are prolific. Their cones are about an inch long and contain from 30 to 100 seeds. They produce seeds almost every year with maximum seed production occurring between the ages of 20–250 years old. They also have an advantage over other species in that new trees can sprout from the roots of damaged or fallen trees.

Unlike the other two species of redwoods, coastal redwoods cannot tolerate freezing temperatures. They thrive in areas below 2,000 ft (607 m), with summer fog, abundant winter rainfall, and moderate temperatures. Although coast redwoods are often found in mixed evergreen forest communities, they can form impressive pure stands, especially on flat, riparian areas with rich soils.

Giant sequoia

The giant sequoia, although not as tall as the coast redwood, is a larger and more long-lived species. Giant sequoias can attain a diameter of 35 ft (10.6 m); whereas the largest Coast redwood has a 22-ft (6.7-m) diameter. The largest tree species by volume, giant sequoias the trees through which roads were built and rangers' residences hollowed out. The most massive specimen, the General Sherman tree, located in Sequoia National Park, has a bole volume of 52,500 ft³ (1,575 m³)

The oldest giant sequoia is 3,600 years old, compared with 2,200 years old for the oldest coast redwood. This makes the giant sequoia the second oldest living thing on earth (the bristlecone pine is the most long-lived).

Giant sequoias can be found between elevations of 5,000 and 8,000 ft (1,517 and 2,427 m), growing best on mesic sites (such as bottomlands) with deep, well-drained sandy loam soil. Unlike coast redwoods, mature trees of this species cannot sprout from the roots, stumps, or trunks of injured or fallen trees (young trees can produce stump sprouts subsequent to injury). It is paradoxical that one of the largest living organisms is produced by one of the smallest seeds. Three thousand seeds would weigh only an ounce. Typically, cones bearing fertile seeds are not produced until the tree is 150–200 years old. The cones are egg-shaped and 2.0–3.5 in (5–9 cm) in length. Once cones develop they may continue to grow without releasing the seeds for another 20 years. A typical mature tree may produce 1,500 cones each year, and because they are not dropped annually, a tree may have 30,000 cones at one time, each with about 200 seeds. Two species of animals, a wood-boring beetle (Phymatodes nitidus ) and the chickaree or Douglas squirrel (Tamiasciurus douglasii ), play important roles in dislodging the seed from the cones. Fire is also important in seed release as the heat drys the cones. Fire has the added advantage of also preparing a seed bed favorable for germination. The light seeds are well-adapted for wind dispersal, often travelling up to a quarter mile away from the source tree.

Like the other redwoods, the wood of the giant sequoia is extremely durable. Because of this durability and the ornate designs in the wood, this species was harvested extensively. One tree can produce up to 600,000 board feet of lumber, enough to fill 280 railroad freight cars or build 150 five-room houses. Unfortunately, because of the enormous size of the trees and the brittle nature of the wood, when a tree was felled, as much as half would be wasted because of splintering and splitting. Now that virtually all giant trees have been protected from logging , the greatest threats from humans are soil compaction around their bases and the elimination of fire which allows fuels to accumulate, thereby increasing the chances of deadly crown fires. Toppling over is the most common natural cause of death for mature giant sequoia trees. Weakening of the shallow roots and lower trunk by fire and decay, coupled with the tremendous weight of the trees, results in the tree falling over. Sometimes wind, heavy snows, undercutting by streams, or water-soaked soils contribute to the toppling. In its natural range this species is now valued primarily for its aesthetic appeal.

[Ted T. Cable ]