Those Difficult-to-Tell-Apart Yews of the Puget Lowlands

The urban forests of the Puget Lowlands support both the native Pacific yew (Taxus brevifolia) and the non-native, naturalized European yew (Taxus baccata).

Yews grow slowly and can live for a long time. A Pacific yew with a trunk only six inches in diameter can be 100 years old. This specimen in Everett’s Forest Park was probably growing before the Douglas fir beside it sprouted from seed.

The Same or Different Species?

According to information about Pacific yew genetics in a 2018 U.S. Forest Service publication (here), “Pacific yew was originally classified as a variety of T. baccata (European yew), which it closely resembles.” Furthermore, “Where different species grow near each other, interspecific hybrids frequently occur, lending support to the view that there is but one species.”

Whether they are the same or different species, the density of foliage and the shape of individual needles can often — but not always — distinguish a Pacific yew from a European yew.

Density of Foliage

On a recent plant tour in Seattle’s Ravenna Park, Arthur Lee Jacobson showed us both species and highlighted differences he has observed. To quote from his book, Wild Plants of Greater Seattle, the needles of Pacific yew “tend to be at the ends of sparse, skinny, drooping twigs.” In contrast, the twigs and needles of European yew are “stronger, glossier, and more luxurious.”

This photo, looking up through the canopy, shows the sparse foliage of an old Pacific yew growing in the understory.

In comparison, the foliage of this European yew is dense.

This small branch of a Pacific yew shows significant loss of needles after only a few growing seasons.

In comparison, this branch of a European yew shows no evidence of losing its needles.

But Not All Pacific Yews Have Sparse Foliage

This small Pacific yew with no dominant leader was planted by the Green Everett Partnership in a shady spot in 2016. Its foliage shows no signs of thinning. This is consistent with an experiment that found that “leaf area was significantly higher in Pacific yews grown in the shade than in the sun.”

This branch from a middle-aged Pacific yew growing under a canopy of Douglas firs is retaining its needles.

For some unknown reason, this mature Pacific yew in Edmond’s Hutt Park is growing at a slant. Its foliage is relatively dense.

Shade Tolerance

The European yew seems to have dense foliage whether it grows in the sun or the shade.

I wonder if lack of direct sunlight might contribute to the sparse foliage on some of the older Pacific yews?

One source states that “where the overstory has been removed or thinned, diameter growth on undamaged Pacific yews may increase considerably.”

Another source indicates that Pacific yews tolerate direct sunlight if they have access to a steady water supply in well-drained soil.

In drier open habitats, Pacific yews can take on a shrublike appearance, forming a dense groundcover and spreading through layering.

Perhaps the Pacific yew prefers shade to become established, but eventually needs a certain amount of direct sunlight to maintain its foliage.

The foliage on this ancient Pacific yew in Everett’s Forest Park grew increasingly sparse in its final years, eventually failing to produce any new growth. Did it starve from lack of direct sunlight or just succumb to disease or old age?

Bark

Shape of the Individual Needles

If density of foliage is not always a clear indication of the species, what other physical characteristics separate them? Jacobson has observed slight differences in the shape of the needles. With European yew, the needles usually taper gradually to a point whereas in Pacific yew the transition is more abrupt.

Comparing the Needles of Pacific Yew and European Yew

Slow Rate of Natural Regeneration

Both Pacific yews and European yews reproduce sexually when birds eat the bright red arils and disperse the undigested seeds. The fact that both species are uncommon in the Puget Lowlands suggests that their natural rate of regeneration is very, very slow.

The European yew is naturalized in our urban forests to some extent (here, page 54). This small European yew amidst other shrubs may have grown from a bird-deposited seed.

Despite having been grown ornamentally in parks and yards for decades, the European yew does not appear to be invasive in our urban forests because of its slow rate of natural regeneration.

Where Does That Leave Us?

In short, density of foliage does not always provide a clear distinction between European and Pacific yews. Though the foliage on European yews is usually dense, not every Pacific yew has sparse foliage. The differences in the shapes of the needles are so subtle that I can’t always tell the difference. I would not remove a yew from the backyard forest unless I was certain it was the non-native European, and if in doubt, I would let it be since the European yew does not appear to be invasive.