Redwood (Sequoia sempervirens)

The following chapter was taken from Silvics of Forest Trees of the United States, Agriculture Handbook 271, prepared by the division of timber management research of the Forest Service in 1965. It in turn was revised from an unpublished 1964 manuscript by Douglass F. Roy, U.S. Forest Service Pacific Southwest Forest and Range Experimental Station.

The range of redwood extends southward from two groves on the Checto River in the extreme southwest corner of Oregon to Salmon Creek Canyon in the Santa Lucia Mountains of southern Monterey Country, California. This redwood belt, which includes about 1.9 million acres of commercial forest land, is an irregular coastal strip about 450 miles long and generally 5 to 35 miles wide. It has a transverse brake along the headwaters of the Mattole River in southern Humboldt Country, California. South of Sonoma County, redwoods grow in detached and irregular areas.

Habitat Conditions

Climate

The mild climate of the redwood region can be classed broadly as super-humid or humid. Mean annual temperatures vary between 50° and 60° F. Differences between mean annual maximum mean annual minimum temperatures vary from 10° or 15° for coastal points to 30° for the eastern edge of the redwood type. Temperatures rarely drop below 15° or rise above 100°. The frost-free period varies from 6 to 11 months (42, 51)

Annual precipitation varies between 25 and 122 inches and falls mostly as winter rain, although snow sometimes covers the highest ridges. Generally, January is the wettest month and August is the driest.

The frequent summer fogs which blanket the redwood region seem to be more important than the amount of precipitation in delineating the redwood type. Fog decreases water loss from evaporation and transpiration and, by condensing on and dripping from tree crowns, adds to the soil moisture supply to some degree. The range of tree is limited to areas where heavy summer fog from the ocean provide a humid atmosphere (9).

Soil and Topography

The parent rock material of the redwood region Is largely massive marine sandstone formed in Tertiary and Upper Mesozoic periods. Considerable shale and lesser amounts of Mesozoic limestones and Franciscan slates, cherts, limestones, and sandstones also are represented, and shists are fairly common in some localities (42).

High-site soils for redwood are the Hugo, Josephine, Melbourne, Empire, Sites, and Larabee series and associated alluvial soils. The high-site residual soils have been derived from either consolidated or soft sedimentary rocks. They are light grayish brown or light reddish brown to brown in color and moderately to strongly acid.

Soil textures grade through loam, sandy loam, fine sandy loam, silt loam, to clay loam (45).

The redwood region generally is characterized by irregular ridges oriented northwest to southeast with deep narrow valleys (44). Redwoods grow from sea level to about 3,000 feet (31) but most are found between 100 to 2,500 feet (42). The best stands have developed on flats and benches along the larger streams, on moist coastal plains, river deltas, moderate westerly slopes, and valleys opening toward the sea. Some of the flats and benches support pure redwood stands of exceptionally high volumes (42).

Although the main bodies of redwood are close to the ocean, redwood does not tolerate ocean winds, and considerable evidence suggests that it is sensitive to ocean salts carried inland during storms. Usually redwoods do not grow on hillsides squarely facing the ocean (32).

Redwoods become smaller and give way to other species as altitude, dryness, and slope increase. In the north, redwoods clothe all exposures (51). In the southern part of the range, redwoods are restricted to western or northern exposures, and in the extreme southern extension they are restricted almost entirely to the bottoms of narrow canyons which cut through steep foothills abutting the ocean. Trees near the mouths of these canyons often are exposed to onshore winds and frequent]y have flat tops with dead limbs on the windward side. This effect has been attributed to the tree's inability to replace moisture lost through desiccation by the winds (27).

On alluvial flats, where redwoods reach their maximum development, soils have been built up by deposits of sediment from successive floods. In one area the ground level had been raised 11 feet in 700 years (15). In another, repeated flooding in the last 1,000 years deposited nearly 30 feet of silt and gravel around the bases of many large redwood trees (50). Deposits from a single flood have been as deep as 30 inches. Redwoods adapt themselves to the new ground levels by originating new and higher root systems (l5).

Associated Trees

Redwood is a principal species in only one forest cover type, Redwood (Type 232), but is found in four other Pacific Coast types, Pacific Douglas Fir (Type 229), Port-Orford-Cedar-Douglas Fir (Type 231), Oak - Madrone (Type 234), and Pondersoa Pine-Sugar Pine-Fir (Type 243).

Pure stands of redwood are found only on some of the best sites, usually the moist river flats and gent]e slopes below 1,000 feet. Although redwood is dominant throughout its range, it generally is nixed with other conifers and broad-leaved trees.

Douglas-fir, the most important associate, is well distributed throughout most of the redwood type. The distributions of other conifer associates are more limited. Important species on the coastal side of the redwood type are grand fir and western hemlock north from northern Sonoma County, and Sitka spruce north from the vicinity of Humboldt Bay.

Conifers occurring less commonly with redwood are: Port-Orford-cedar, Pacific yew, western red cedar, and California torreya.

The two hardwoods which are most abundant and generally distributed in the redwood type are tanoak and Pacific madrone. Other hardwoods found in the redwood type are: vine maple, big-leaf maple, red alder, golden chinkapin, Oregon ash, Pacific waxmyrtle (Myrica californica), oregon white oak, cascara sagrada ( Rharunqls purshiana), willows, and California-laurel.

Life History

Reproduction and Early Growth

Flowering and Fruiting

Redwood blooms between late November and early March although flowering usually is over by the end of January (41). Weather conditions during flowering may directly affect seed quality. If flowers open during a continuous rainy period, pollen is washed from the pollen strobili. Little pollen may reach the conelets. Dry periods during flowering permit optimum dispersal of pollen and help produce seed crops of high viability.

Redwood cones are terminal and 1/2 inch to 1-1/8 inches long. They mature the autumn after flowering (41) and open from early September until late December (25). Although cones persist for several months, they open and shed seed soon after ripening.

Seed Production and Dissemination

Redwoods generally produce abundant seed almost every year (23, 47). Even trees in the intermediate crown-class often produce seed crops (21). The minimum age for good seed-bearing is 20 years; the optimum, from 60 to 100 years.

One study showed that seed viability increased with the age of the parent trees. The maximum was reached when trees were more than 250 years old. Seeds produced by trees under 20 years old generally were less than 1 percent viable, and seeds from trees over 1,200 years were sterile or not more than 3 percent viable (41) .

Trees with new, narrow crowns resulting from sprouting of dormant buds after fire has killed the crown produce few cones during the first 4 years after the fire. About half such narrow-crowned .trees, locally called fire-columns, bear cones in the fifth year, however, and almost all produce cones the seventh or eighth year.

The germination rate of redwood seed is usually low. Poor germination often is caused by the high percentage of empty seed rather than by dormancy. When obviously defective seed are removed, germination may be as high as 79 percent ). In one seed study soundness varied significantly with seed size. Seeds passing 12, 10, and 8 mesh screens were 2, 8, and 15 percent sound, respectively. Seeds from seven sources recently photographed by X-rays. The distribution seeds in categories was: empty or tannin filled, 58 to 97 percent; seeds with embryos damaged by fungi, 0 to 11 percent; and sound seed, 1 to 32 percent (28).

Redwood seed does not seem to store well. One seed-lot was stored successfully for 3 years, but lost its viability completely after 5 years (46).

Redwood cones dry readily under conditions of low humidity and quickly release their seeds with slight shaking. But because weather conditions at cone ripening usually are unfavorable for rapid drying, seed dispersal may be spread over periods varying considerably in length.

Rains, however, may hasten seed dissemination. One observer found in many instances that redwood seeds remained in the open cones until a drenching rain dissolved the tannic crystals in the cones .

Seed dissemination during the winter months seems characteristic of redwood in the northern stands. Over four-fifths of the sound seed in one study was shed during December and January (5). Redwood seeds are small and light, about 123,000 the pound, but lack efficient wings to slow them in falling. They fall at rates between 4.9-20.5 feet per second, averaging 8.6 feet. These rates are faster than for most other forest seed and limit seed dispersal considerably (48).

Timbered edges of clear-cut units have effective seeding distances of only 200 feet uphill and 400 feet downhill under average redwood stand conditions (43). A recent study in Del Norte County showed that the largest clear-cut units should be nearly round or square and not more than 30 to 40 acres.

In partially cut stands in Mendocino and Humboldt Counties, the minimum number of seed trees needed to provide acceptable stocking varied from 4 per acre on north slopes, with favorable ground conditions, to 8, or more, for southern exposures (43). In Del Norte County, more than 1.4 million sound seeds per acre fell under a shelterwood stand of 3 seed trees per acre and 4.4 million seeds fell in a selection cutting where 14 seed trees to the acre were reserved (5).

Seedling Development

Redwood seed generally is ready to germinate soon after it falls to the ground if seedbeds are moist and the weather is warm enough. As a rule, seed do not require pre-treatment for germination. Occasionally, germination has been improved by stratification, indicating slight and variable seed dormancy.

Mineral soil is the best seedbed, but seed will germinate readily in duff, on logs, in debris, or under other vegetation, and in either shade or full sunlight if adequate soil moisture is available (19, 21, 23, 41, 43, 52). Redwood seed germination is epigeous.

New redwood seedlings require a greater supply of soil moisture for survival than that needed by seedlings of most associated trees. Late spring and early fall rains can be critical survival factors (23). Redwood seedlings on fully exposed soil can withstand considerable surface heat if their roots have reached an abundant permanent moisture supply. Otherwise, they die before soil surface temperatures reach 140° F. (23).

In its early stages redwood grows rapidly in both height and diameter. Seedlings often grow 18 inches in the first season (11) and trees 4 to 10 years old commonly grow 2 to 6-l/2 feet in a year (31).

Juvenile growth of redwood is best in full sunlight. Although redwood seedlings can endure heavy shade, growth may be slow (19). Photosynthesis in redwood is remarkably efficient at low light intensity. This tree grew vigorously in much weaker light than 12 other tree species studied. For example, it increased its size 8.8 times in 10 percent of full sunlight in a 9-month period, more than twice the growth of any other species. For appreciable growth Engelmann spruce and Douglas-fir require twice as much light as redwood. Pines require three to four times as much (2).

A diurnal temperature variation is not required for maximum growth of redwood seedlings (30). Roots developed better in the laboratory at a soil temperature of 64° F. than at 46° and 82° (29).

A l-year-old tree may have roots only 3 inches deep in compacted soils, but in loosened soils roots will be more than 12 inches deep and abundantly branched (19).

Radial growth of redwoods in Mendocino County at points 4, 9, and 20 miles from the coast did not vary very markedly in growth pattern.

Radial growth began after mid-March, increased to a maximum in late May, and then declined at fairly uniform rate to a minimum at the end of September. Growth was negligible from October 1 to March 15 (3).

Vegetative Reproduction

Redwood can be propagated by cuttings (41), but no large scale attempts at this kind of reproduction have been reported. In one study 40 percent of the cuttings from the tops of fast growing seedlings, pushed into forest nursery soil with no special treatment developed new root systems (11).

The ability of redwood to sprout from root crowns at any season of the year within 2 or 3 weeks after logging is an unique characteristic. Numerous and vigorous sprouts originate close to the stumps from adventitious buds on the large lateral roots. In one study where the average stump diameter was 35 inches, there were 72 sprouts per stump on the average (41). Stumps often are circled by more than 100 sprouts (31, 32). Each sprout soon develops its own root system and in a remarkably short time the dominant sprouts create circles of new trees around the old stumps.

Sprouts may develop from root crowns on trees of any age, but this ability is strongest on the better forest sites and in smaller trees. In one study, 62 percent of all redwood stumps sprouted, Eighty-one percent of the stumps less than 56 inches in diameter sprouted, but only 36 percent of the stumps over 126 inches produced sprouts (52).

Sprouts are commonly 21 to 36 inches high at the end of the first year, but they be may be more than 6 feet tall (11. 18) . In one case a fire killed all the sprouts around a stump. About 300 new sprouts appeared at once, and at the end of one growing season many reached 7 feet (11). Sprouts grow more rapidly than seedlings and the initial impetus lasts many years .

Early estimates of stocking from root crown sprouts varied from 20 to 35 percent of full stocking (10, 37). Later, these estimates were recognized as high because they apply only when the best quality pure redwood stands, found on riverside benches, are logged (41, 47). Redwood sprouts on typical cutover redwood land in Mendocino and Humboldt Counties provided only 8 percent of full stocking (42).

Redwood also can sprout along almost the entire length of its trunk. If the crown of a tree is destroyed by fire or by logging damage, numerous dormant buds along the trunk are stimulated and produce new foliage. Most of the trunk will be covered by feathery foliage extending 2 or 3 feet from the trunk (31). Eventually, normal crowns develop again.

Even where fire burned away the tops of trees in plantations less than 2 years old, most of the seedlings sprouted again (38).

Growth and Yield

Redwood is long-lived, grows taller than any other tree in the world, and is exceeded in bulk only by the giant sequoia. Redwoods are mature at 400 to 500 years (31 32, 51). The age of the oldest tree found so far is nearly 2,200 years, determined by growth ring counts (22).

Redwood forests sometimes are incorrectly called even-aged and overmature, when, in fact, no other forest in the world can match many redwood stands in range of ages and mixture of vigorously growth and decadent trees (12).

Redwood probably is best known for its great size, although the average redwood is smaller than commonly believed. Trees larger than 12 inches in diameter on a 30- acre tract typical of Humboldt County, fell approximately into these divisions 12 to 30 inches in diameter, 50 percent; 31 to 60 inches, 32 percent; 61 inches and larger, 18 percent (12). Redwoods 12 to 16 feet in diameter found scattered all over the entire range, are considered large. Trees 20 feet or more in diameter at a point 5 feet above the ground are rare (12, 22).

Redwoods more than 200 feet tall are common and many trees growing on the river-side benches where the soil is deep and moist, are taller than 300 feet. The tallest redwood was 368.7 feet in 1956 (22).

Large trees and dense stocking combine to produce high yields. Over 81 percent of the commercial redwood forest land is classified as highly productive and only 3 percent is poor for growing trees. Individual acres yielding 100,000 board feet of saw timber are common, even on slopes (11). Recent cuttings in Del Norte County, on units of 13 acres and larger, produced gross volumes ranging from 95,000 to 280,000 board feet (Scribner) per acre. Defects in logs hauled was about 12 percent, and about 40,000 board feet of cull logs and broken wood was left on the grown. The number of merchantable trees varied from 29 to 46 per acre, and tree sizes were from 14 to 198 inches in diameter (4, 6). Flats along rivers have yielded more than 1,000,000 board feet per acre in scaled logs (7, 12, 13, 22, 51).

Young-growth redwood is often as spectacular in size and yield as old growth. Dominant young growth trees on good sites are 100 to 150 feet tall at 50 years, and 165 to 220 feet at 100 years (4). Height growth is most rapid up to the 35th year (35).

Diameter growth of individual young trees can be rapid or very slow. In dense stands where competition is severe, annual radial increment is commonly as little as 1/30-inch. Occasionally there are 100 rings per inch. At the other extreme, radial growth is as much as 1 inch a year. One redwood growing with little competition was 84 inches in diameter at 108 years of age (22).

The yield of young-growth redwood stands at 100 years is expected to range from 56,000 board feet per acre on low sites to 350,000 board feet on high sites. Much of the acreage now under management will grow 2,400 board feet per acre per year (34).

Natural pruning in young redwood stands often is not good. Although live crown may be limited to no more than the upper third of the trunk, dead limbs are persistent. Stubs, although decayed, may remain over 50 years. In old trees some branch stubs have affected the quality of the timber over a 200-year period (21, 23). Trees in the intermediate crown class, however, often prune well naturally (23), and some trees in a heavily stocked stand have clean trunks for 75 to 100 feet at 85 years (18).

Reaction to competition

Redwood has been classed as tolerant or very tolerant in a scale of 5 tolerance classes (1). Redwood stands are dense. The average well stocked acre supports nearly 1,000 stems at 20 years, including 500 dominant and codominant trees. At 60 years redwood has a basal area of 486 square feet on the best sites (8) . Heavy stocking is desirable because the relatively high tolerance permits an acre to support a large number of dominant and codominant trees.

Redwoods can endure suppression almost indefinitely. A 10-inch suppressed tree might be well over 100 years old (16). Small trees may be suppressed for over 400 years but still maintain a remarkable capacity to accelerate growth rates when released if they are not injured seriously during logging or slash-burning (17, 40).

Large trees also can accelerate growth when released from competition. A l,000-year-old tree, for example, increased its radial growth from 30 rings to 6 rings per inch when it was only partially freed from competition by clearing on a highway right-of-way (21).

The redwood forest is a climax type. When growing with other species redwood is always a dominant tree.

Principal Enemies

Fire is redwood's worst enemy. Young stands may be killed outright by a single ground fire (51). Fires are especially damaging to reproduction under 20 years old because their thin bark does not protect young trees. Also, more flammable litter lies on the ground, and the micro-climate is drier than under old-growth forests (14) .

Old-growth redwood stands show evidence of three or mole severe fires each century (22). In many cases fires may only reduce the thickness of the protective bark, which may be a foot thick. In other cases fires cause basal wounds through which heart rots enter. The combination of recurring fires and advancing decay produce large basal cavities called "goose pens" (14). In extreme cases mature trees may be so weakened mechanically that they fall (24).

Redwood has no tree killing diseases but heart rots cause extensive cull. Most common heart rot in the southern part of redwood's range is a brown cubical rot, caused by Poria sequoiae. A white ring rot caused by P. albipellucida is most important further north (33).

A twig and branch canker (Coryneum sp.) has been observed on sprouts and plantation trees of seedling and sapling size. This canker, which girdles small stems and branches, could become damaging in plantations.

Several insects are found on redwood but none cause significant damage. These include a flat-headed twig borer and girdler (Anthaxia aeneogaster), two redwood bark beetles (Phloesinus sequoiae and P. cristatus), and the sequoia pitch moth (Vespamima sequoiae).

Bark stripping by the American black bear has become serious in some parts of the redwood region (20) . Wide strips of bark are ripped from the tree, often from the top to the ground, during April to August. Trees 10 to 30 years old and 6 to 10 inches in diameter are damaged most (26) and may be girdled (39).

Redwoods have no tap roots, but lateral roots are large and wide-spreading (11, 51). Small trees have better than average wind-firmness (23) and larger redwoods are wind-firm under most conditions (36, 51). In partial cuttings the smaller codominant and intermediate trees are most frequently blown-down (4).

Special Features

A prominent special feature of the redwood is its production of burls from which beautifully figured table tops, veneers, bowls, and other turned products are cut. These burls are found on any part of the trunk and in sizes varying from an inch to many feet in diameter. Their cause is unknown.

Another feature of redwood is its extremely tough and fibrous bark. This bark must be removed before logs reach the head saws so that sawing uniform lumber will be possible (17).

Races and Hybrids

Races of redwoods are not known.

In Russia hybridization of redwood with giant sequoia, baldcypress and Japanese cryptomeria (Cryptomeria japonica) has been reported (53).

An interesting hypothesis concerning the origin of redwood, with a diploid number of 66 chromosomes, is that redwood originated as an allopolyploid from hybrids between an early Tertiary or Mesozoic species of Metasequoia, and some probably extinct Taxodiaceous plant like the modern giant sequoia, taiwania (Taiwania cryptomeriodes), or Tasmanian cedars (Athrotaxis spp.) (49).

Literature Cited

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