Location: On the edge of the drive leading down to the Burke Museum parking lot on the downhill side (west), growing in the median just past the sidewalk which runs parallel to the drive.

Summary: Our first specimen of the native tree tour is one who has specialized as a riparian species, a type of plant whose preferred habitat lies along the streams, rivers, and wetlands of our region. The Oregon White Ash is a relatively small tree for the Pacific Northwest, generally achieving a height of about 80ft. Such a size would make it difficult for the species to compete in amongst the coniferous giants which make up so much of the western forests of Washington, but the open nature of riparian habitats allows sun to shine brightly on the light green foliage of the Oregon Ash. River and stream habitats often experience sudden changes in the form of floods, which can create new opportunities for growth, but also knock down existing trees. As a result, this species benefits from a fast rate of growth, achieving large mature sizes within a few decades to take advantage of suddenly available sunny growing spaces.

The Oregon White Ash has dense hard wood, whose strength makes it a preferred source of traditional tools such as canoe paddles and digging sticks amongst indigenous peoples of the region. It has also been incorporated into tool handles, and exhibits properties which make it a fair substitute for the popular Eastern Ash timber. In the past few years, this native tree has come under threat of a newly introduced insect from Asia, the Emerald Ash borer, which has been detected in the Portland area. As populations of this insect increase, it is likely to place major pressures on this native hardwood. Movement of ash trees (and several other plant species that are known hosts for this insect) is illegal within areas of infestation.

Identifying Features light: A deciduous tree with smooth gray to brown bark becoming ridged and thinly scaly with age, this species is defined by being one of the very few in the Pacific Northwest to exhibit compound leaf structure. A compound leaf is composed of a central stalk with opposite leaflets on either side and often a terminal leaflet on the end. The leaves of this species are therefore composed of 3-9 (most often 5-7) small leaflets 3-7” in length, with the overall size of the leaf being about 5-14” in length. The twigs these leaves are born upon are thick and round, and often have fuzzy hairs which persist into their second season. Winter buds bear 4-pairs of hairy scales, and appear in spring in the light pleasant green of this species. The crown of these trees grow to be open and conical, with stout angular spreading branches. In drier regions it is often a riparian species, lining streams and riverbanks in immensely pleasant groves.

Identifying Features In Depth:

1. Form: A large deciduous tree, growing to a height of about 80’ (25 m) and a diameter of 2-3’ (0.6-0.9 m). When mature in good conditions it displays an open crown with stout spreading branches and a conical form, but when growing in exposed regions it may be short and thick and in thick forests it may appear as a very thin trunk with a thin crown. In perfect conditions it may achieve heights of 150’ (45 m) or greater.

2. Leaves: Leaves of this species are compound, growing with 3-9 (usually 5-7) leaflets. These leaflets have a length of about 3-7” (7.6-17 cm), while the overall length of the leaves is between 5-14” (17.5-35.5 cm). They have a stout grooved stalk angled out from the stem, and are light green with a pale vein in the middle of each leaflet. They are sometimes hairy, and veins are distinctly curved forward at the edges.

3. Bark: The bark of these species is a dark gray or brown, often tinged with red undertones, growing in thin scaly ridges with deep seams in between. On older trees bark may reach over an inch thick, ridged into furrows much like on a bigleaf maple. Twigs are thick and either hairless or, when new, exhibiting a pale rust colored fuzz persisting to the second year of growth.

4. Reproductive Bodies: This species is dioecious, meaning male and female flowers occur on separate trees. These flowers appear just as the leaves are bursting from their buds, and grow in small compound clusters. These give rise to fruit between 1 and 2 inches (2.5-5 cm) growing in dense clusters. Each fruit is an oblong single winged seed, often notched at one tip and pointed at the other.

Historical Background: A lover of moist bottomlands and riparian habitats, this tree can play an important role in such ecosystems, growing along with maple and birch in those places just a bit too soggy for conifers of the northwest. As a timber tree, it has been prized due to its status as a hardwood in a climate dominated by softer board types, and it is therefore prized in the northwest for furniture and finish, as well as in woodworking. A shorter lived species, these trees may yet achieve more than 200 years of age in the right growing conditions where light is ample. In a forest setting their form is spindly and narrow, stretching for the light, but in the open they may spread to a broader (yet still cylindrical) growing habit. According to the lore of early trappers and indigenous people of Oregon, venomous snakes do not inhabit regions where ash grows, and thus a branch of ash may protect one from a rattlesnake. The fresh root of these trees were crushed as a poultice for the treatment of serious wounds by some indigenous tribes, while others used a cold infusion of the twigs to treat fever. The bark is known to be anthelmintic, meaning it kills parasitic intestinal worms.

Native Range: The Oregon White Ash occurs from coastal British Columbia south to Monterey Bay in California, and inland in the Cascades and Sierra Nevada all the way south to California’s San Bernardino mountains.