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The tree that fights cancer.

The whistle punk gave the signal, and the huge Douglas-fir log began to move up the mountainside, hauled by heavy cables and knocking down everything in its path: hemlock saplings, clumps of vine maple, and yew trees. After the logs were yarded, the leftover debris-including the yew was burned in hot slash fires.

As that incident indicates, the small, understory Pacific yew (Taxus brevifolia) was long considered a trash tree of no value. Today the news is that this lowly conifer has become the Cinderella of the Northwest woods. An unusual chemical called taxol, extracted from the bark of the Pacific yew, has been found useful in the treatment of ovarian cancer and is undergoing testing for other kinds of cancer. (See The Lifesaving Yew Tree- on this page.) Other species of yew (there are seven worldwide) also contain taxol, but Pacific yew yields more of this compound than does any other yew and remains the chief source. Efforts have been made to synthesize taxol, but all attempts so far have failed. A company in Washington state, Advanced Molecular Technologies, has a contract to supply the National Cancer Institute with 60,000 pounds of dried bark. This much bark is expected to yield about nine pounds of the cancer-fighting drug. Pacific yew bark is thin, about 1/8 inch thick, and it will take 2,000 to 4,000 trees to supply 2.2 pounds of the drug. Rather than cutting yew trees specifically for bark extraction, the company is using yew salvaged from areas recently logged. If clinical tests currently in progress are successful, large quantities of taxol will be needed, and Pacific yew will become an extremely valuable tree. So valuable that its continued existence could be threatened.

Pacific yew is a dwarf among the giant conifers of the Pacific Northwest. Yew trees grow 20 to 30 feet high and six to 12 inches in diameter. The record Pacific yew, located in Lewis County in western Washington, is listed in the American Forestry Association's National Register of Big Trees as being over 41/2 feet thick and 54 feet tall.

The oldest yew trees may live to be over 500 years old. I counted 260 annual growth rings on one 14-inch yew after it was cut.

Even before its promise as a cancer cure became known, the diminutive Pacific yew was far from completely worthless. Growing very slowly in deep shade, it produces dense, fine grained wood. Small amounts of this durable wood have been used traditionally for canoe paddles, archery bows, and cabinet work. The small size of the tree also makes it attractive as an ornamental.

This shade-tolerant species occurs over a large area of western North America, but it is not abundant throughout most of its range. It is found from southeastern Alaska to coastal British Columbia, Washington, Oregon, and northwestern California. Isolated trees are seen almost as far south as San Francisco. It is also found in the Sierra Nevada, where its southern limit is the Calaveras Big Tree State Park. The inland range extends from the western slope of the Rocky Mountains in British Columbia into northern Idaho and western Montana.

Pacific yew grows scattered in small groups or as isolated individuals rather than forming large, contiguous stands. An exception is a curious region on the south fork of the Clearwater River of northern Idaho where Pacific yew forms nearly impenetrable, jungle-like thickets.

The tree's sparse foliage and small size make it inconspicuous in the forest, and it is thought to be rare, yet this shadowy tree is more common than is generally recognized. In some areas of the Sierra Nevada, Pacific yew is abundant in almost every moist canyon and is scattered on the shady uplands. In Washington state I have seen yew growing on moist riverbanks, on dry, rocky glacial outwash, and hidden beneath towering old-growth Douglas-fir.

In my own small tree farm of 80year-old Douglas-fir, I found two large yew trees that I had passed many times without taking notice. I also found several tall, vigorous saplings and a number of seedlings that came up after the Douglas-fir were thinned six years ago.

I have not been able to determine yet whether my two large yews are male or female trees. Pacific yew, in common with other yews, does not have both male and female flowers on the same tree. Male trees produce small yellowish flowers abundantly on the underside of the branches. The less numerous greenish female flowers are hidden behind the base of the leaves, and after they are fertilized turn into scarlet, berrylike fruit eaten by birds. The seeds are disseminated throughout the forest by passing undigested through hungry birds.

Pacific yew can also reproduce vegetatively. I have seen yew knocked down by logging that had formed dense thickets of sprouts all along the stem of the down tree. One immortal old yew knocked over decades ago by a falling tree had sprouted a new tree from its base that was nearly as large as the original tree. Lower branches of Pacific yew that come in contact with the soil will form roots, and cut stumps will sprout.

A task force from the Pacific Northwest Research Station of the U.S. Forest Service was recently organized to report on the current knowledge of Pacific yew and to recommend research needed to study its growth and propagation. Pacific yew's ability to regenerate by sprouting could be its salvation. Dr. M.A. Radwan of the U.S. Forest Service laboratory in Olympia, Washington, has successfully rooted cuttings of Pacific yew and has shown that the tree can be propagated this way. The genetics team in Corvallis, Oregon, has also rooted cuttings. Thus crops of yew trees for the production of taxol could be grown from stem cuttings or stump sprouts.

The great western woods have revealed the secret of the invincible Pacific yew. What's next? Other forgotten western trees may well turn up someday and provide additional lifesaving drugs. AF (The U.S. Department of Agriculture announced a year ago that it has successfully grown Pacific yew cells that yield taxol. But Donna M. Gibson, a USDA plant physiologist who worked on the research team that isolated the drug-producing cells, says the problem is that producing taxol in a laboratory is not yet cost-effective. "We have the method for growing the taxol-producing cells, but now we need someone interested in working on scaling the method up to a commercial level."
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Title Annotation:includes related article; Pacific yew
Author:Murray, Marshall D.
Publication:American Forests
Date:Jul 1, 1991
Previous Article:Problems & progress in tropical forests.
Next Article:The wall within.

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