Yew Are Everywhere

Aril fruit of T. baccata

The yew is one of those ubiquitous foundation shrubs that far more people recognize than know its name. They are planted next to private homes and in public parks all over the Northern Hemisphere in part because they are relatively slow growing and but also because they are highly resistant to air pollution. They occasionally draw attention to themselves because they are poisonous to eat and children may have difficultly resisting the bright red berries (arils) on the female plants (the yews are dioecious). On the other hand, all yew species produce taxol, a chemical that has been used in cancer treatments.

My own fascination with yews might have started at age 10, when we moved into a 19th century Victorian house that had several large specimens growing in beds along the east side of the house. They had become greatly overgrown, crowding over the stairs that led into the house and with their branches pressed up against the shingles. In one bed two white cedars (Thuja) hung over the yews, leaning away from the house because they had been planted only about three feet from the foundation.

My mother, determined to bring some order to the landscape, organized a family project to cut down all of these conifers to stumps. At the age of 10 this struck me as pretty nearly criminal because this thicket of evergreen foliage and sturdy low-lying limbs seemed like a perfect hideout. I also had a somewhat reflexive idea that perfectly healthy trees shouldn’t be cut down and remember arguing for some less radical pruning.

Enormous yew hedge at Powis Castle

In the end only two of the yews and two of the cedars were cut back, and my mother, who literally owned a set of horticulture encylcopedias, assured me that the yews would grow back and that the cedars, like most conifers, would not sprout from stumps. I only half-believed her until the yews did actually begin growing back. For a while they looked like abstract sculptures erupting from the ground, but after three or four growing seasons they were shrubs again, now much more reasonably sized.

It may have been when I was in college that I learned that there was actually a yew native to the northeastern United States, and that I had never seen it because deer had browsed it into rarity. Taxus canadensis is found from Newfoundland and Labrador west to Manitoba and south in the mountains to Tennessee and Virginia. It is, however, listed as threatened or endangered in several states.

Over the years I have seen it only rarely in the woods, most recently far up Taughannock Gorge near Ithaca, where I have never seen a deer. The deer must, however, browse those yews because they are quite small. The area has been parkland for decades and yew can grow to be 20 feet tall if left undisturbed. The Taughannock specimens are spindly stalks perhaps two or three feet high.

There are large yews in the village park at the corner of McLallen and Old Main streets in Trumansburg. These are large specimens, approximately 15 feet tall, but they unlikely to be the native species. Most yews planted in designed landscapes are Japanese yews (T. cuspidata) or one of the many hybrids developed by crossing the Japanese species with one of the seven other species found in amazingly varying environments throughout the Northern Hemisphere. The Trumansburg park shrubs have been heavily browsed by deer, but they are actually too tall for the deer to reach the top third of the foliage. This gives them an unintentionally graceful appearance, their many anastomosing trunks nearly denuded of greenery resemble squat, coniferous versions of African acacias, the lower limbs of which are heavily browsed by antelope and giraffes.

In their native habitat yews are understory trees, which means they are adapted to doing well with relatively limited light. This also endears them to landscapers. The Trumansburg park yews seem impressively healthy growing beneath several towering sugar maples. The shallow root systems of maples often make it difficult to grow anything beneath them.

The bark of the Pacific yew, former source of taxol

Pacific yew (T. brevifolia) grows in the understory of the towering coniferous forests of the Northwest. It is less common than it once was in part because of logging operations; clear-cutting machinery tends to destroy the understory trees in the process of removing the canopy trees.
But there is a large demand for yew bark because of its importance in cancer research and overharvesting is depleting the shrubs in some parts of its range. According to Gordon Cragg of the National Cancer Institute:

In 1988, the NCI acquired 27 700 kg (60,000 lb) of dried Pacific yew bark, collected from trees cut down in southwestern Oregon. On average, one yew tree yielded 18 kg (40 lb) of green bark, which weighed about 9 kg (19 lb) dried (7). From the 27 700 kg of dried bark, about 4 kg (9 lb) of dry, crystalline taxol was extracted. Clinicians in several locations across the country have asked for increased supplies of taxol to expand tests to a broader range of cancer types. In January 1989, the NCI solicited another 27 700 kg of yew bark.

Cragg acknowledged that the harvest of Pacific yew was not sustainable.

By 1993 Bristol Myers Squibb had developed a laboratory process to produce taxol from a cell line propogated in an aqueous medium and that effectively ended the threat to wild Pacific yew.

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