The coast redwood, Sequoia sempervirens, also known as the California redwood and the giant redwood is an evergreen, long-lived monoecious[1] tree. The species, which is one of the longest lived of all living things (1200 years to 1800 years) on earth, also includes the tallest of all known living things. Specimens well above 61 metres (200feet) are common and many specimens grow above 91 metres (300feet). The coast redwood was very widespread along the Pacific west coast of the United States from California (apart from Southern California whose poor rainfall pattern does not support the tree) right up to the south west corner of the State of Oregon. According to the best current estimates, these giant trees occupied more than 8,500 square kilometres (2 million acres) prior to 1850 when widespread commercial logging began along the Pacific coast. Since then, more than 95% of the original growth has been cut down for timber.
A study of pre-historic fossils indicate that the tree was much more widely distributed in the past than it is today, extending its natural habitat well into Europe and Asia. More recently, the coast redwood has been successfully transplanted from the Pacific coast of America to other areas, most notably New Zealand. Other areas where the coast redwood has thrived include Britain, South Africa, Texas and Italy.
Being hermaphroditic trees, coast redwoods can reproduce either sexually or asexually. Sexual reproduction, by means of seed production, begins when a tree is between 10 and 15 years old. Seed crops are large and occur frequently, but seed viability is poor less than 15% of all dispersed seeds being viable. The seeds, which are very small and light, are winged and they depend on wind action to move them to potentially good ground. However, their wings are extremely inefficient, at least when compared to other seeds that depend upon wind action for dispersal and on average seeds are carried only about 60 to 120 metres (200 to 400 feet) away from the parent tree. Where the seed takes, growth is extremely fast; young trees can attain heights of up to 20 metres (65 feet) in just 20 years!
The trees can also reproduce asexually, sprouting from the root crown, a stump, fallen branches or even, when a tree falls over, along a fallen trunk (this explains why many coast redwoods grow alongside in extremely straight lines. These sprouts also exhibit extremely rapid growth with heights of up to 2.3 metres (8 feet) having being recorded in just a single growing season.
Another way in which the tree reproduces asexually is by means of burls. i.e. woody lignotubers[2] which can appear at points from below the soil line up to about 3 metres (9 feet) above the soil line. These burls are capable of sprouting into new trees when they are detached from the parent tree.
Given proper climatic conditions, the coast redwood can be expected to live a very long life, grow very tall and very large. In its native environment, the tree is better equipped than most others for survival. The coast redwood’s bark is very thick and extremely rich in tannin[3] and serves as protection from insects and fires; two sources of extreme danger to the other trees with which the coast redwood shares its habitat. Indeed, increasing understanding of the nature of the coast redwood indicates that where wildfires occur, the increasing severity of such fires is directly related to the abundance of the tree. Indeed, following the great fire of San Francisco in 1906, the chief engineer of the city’s fire department declared that but for the extensive use of coast redwood timber as the primary building material in certain districts of the city, the ravages of the fire would have been decidedly worse.
Clearly then, the major threat to the life expectancy of a coast redwood is man and the activities that he engages in. as we have seen, more than 95% of the trees that existed less than a couple of centuries ago have vanished. Of course, since then, many areas that contain these great trees have been put into some form of protection or the other. But the real guarantee of the continued existence of the coast redwood is its immense value to man. Its beauty, light weight, resistance to decay, resistance to fire, etc. makes it extremely desirable, and there has been extensive cultivation of the tree in many diverse locations. In California alone, about 3500 square kilometres (900,000 acres), almost half of the acreage destroyed after 1850, of redwood forests are managed for timber production. This entire acreage consists entirely of secondary growth, i.e. it has been cultivated by man. It seems then that the coast redwood will continue to thrive for the foreseeable future.
[1] Monoecious plants are hermaphroditic plants which have separate male and female flowers on the same plant.
[2] A starchy swelling of the root crown possessed by some plants as a protection against destruction of the plant stem by fire.
[3] Any of a group of compounds found in plants which play a role in protection from predation, and perhaps also as pesticides, and in plant growth regulation.
