Native Plant of the Month: Oregon Ash (Fraxinus latifolia)
By Erica Guttman
The October sunshine we’ve recently been enjoying in South Sound has highlighted an often overlooked member of our local forests, the Oregon ash. With its lemon-colored fall foliage glimmering against the bright blue sky, it looks like a misplaced Eastern hardwood. Indeed, there are 16 other species of ash growing in the Eastern and Midwestern U.S., but the Oregon ash is the only one native to the Pacific Northwest.
What’s in a Name?
The scientific name for Oregon ash is Fraxinus latifolia. “Fraxinus” is simply the Latin word for “ash tree,” and “latifolia” refers to the leaves, whose leaflets are broadly oval in shape.
The derivation of the word “ash” is harder to pinpoint. Pojar and MacKinnon suggest that it is related to the Latin “ascia” (axe) or “axis” (axle) since the European ash was strong enough to be used for these purposes. The Anglo-Saxon word “aesc” means both “spear” and “vessel,” other common uses.
Ashes are placed in the Olive Family (Oleaceae), which also includes lilacs, forsythias, and edible olives. The Oregon ash is the only native representative of that family in our region. (Note that mountain-ash is an entirely different plant, in the genus Sorbus and in the Rose Family.)
General Description
The Oregon ash is a deciduous tree that grows 40 to 80 feet tall. With oppositely-arranged branches and leaves, it has a striking form in any season. The branches thrust outward almost parallel to the ground, and then turn upward in a candelabra-like form. When growing in the open, ash will develop a broadly spreading crown that from a distance will make it resemble a big-leaf maple. When in crowded stands, it develops a narrow crown as it seeks light skyward.
The leaves are pinnately compound, which means that each leaf stalk has five, seven, or (rarely) nine leaflets arranged across from each other with a single leaflet at the end. The tree’s fullness comes from these leaves, which can be over a foot long and up to a foot across.
The ash is dioecious: the yellowish male and greenish female flowers are borne on separate trees. Clusters of inconspicuous flowers appear just before the leaves, and the females evolve into clusters of one-seeded single samaras (imagine half of a maple “helicopter”), one to two inches long. Every three to five years, an ash produces an especially large seed crop.
The bark on older ash wood is dark-gray or brown, thick and deeply ridged. On young twigs, bark is olive green to almost black. In winter, its opposite arrangement and distinctive buds make it easy to identify: leaf buds resemble brown, hairy deer hooves, which develop above a horse-shoe shaped scar where the previous year’s leaf stalk fell off.
Distribution and Ecology
A truly western species, the range of Oregon ash is limited to the Western side of the Cascade Crest and Sierras from southwestern British Columbia as far south as central California, and then in a narrow band along the foothills of the Sierras. It grows from sea level up into the foothills to about 2,500 feet.
Oregon ash is most commonly associated with wetland edges and riparian zones, where it thrives in rich, fertile, saturated soils. Locally, one can see beautiful stands along the beaver pond at McLane Creek Nature Trail or along the river at Nisqually National Wildlife Refuge. The ash is also at home in sandy or gravelly soils, and one can see mature trees dotting the greens in the sandy, upland soils of the public Tumwater Municipal Valley Golf Course.
Oregon ash has a massive, widespread root system that keeps it windfirm in even the most saturated soils. In addition to sprouting from seeds, new trees can also regenerate from stumps. Ashes are fairly long-lived — to about 200 years or even more — but they put on most of their growth as young trees and then grow very slowly as they age. When left alone and occupying favored conditions in wet soils, ashes can achieve even greater heights of 150 feet or more with a pole-straight trunk. In poorer soils, the tree’s form becomes crooked.
In the Landscape
With a splendid candelabra-like form and beautiful year-round color, the ash is a great tree for any yard with a bit of space. Although its primary habitat is in wet areas, it will tolerate drier conditions, and our seasonal rainy deluges ensure it will have plenty of moisture for at least half the year! Ash is especially attractive as a shade tree near the house, which then lets in plenty of light during the winter months. Since its roots are windfirm, it will offer comfort to those who are concerned about trees falling on their homes.
Ash in the home landscape will be most attractive in full sun. It is intolerant of shade, and so will be less full if forced to occupy crowded conditions. Ash is an especially fine choice for anyone trying to plant to manage seasonal flooding, or restoring a wild area on the property.
Ash is attractive to a variety of birds, offering nesting sites, protection, and food. It is also a good food source for beavers and other small mammals, as well as deer. Occasionally, an unattractive but benign, fungal blight may temporarily interfere with the tree’s beautiful foliage late in the year.
Ethnobotany
Like its Eastern counterparts, Oregon ash has an extremely hard wood that is ideal for tools and furniture. Look at a quality baseball bat or shovel handle to see the wide-ringed growth from the core of the ash, which is more elastic than the more brittle wood of the older (outer) growth. Ash was a favored wood of Northwest Natives for canoe paddles and digging sticks.
Oregon ash also has a strong cultural history in protecting against poisonous snakes, who are said not to crawl over an ash stick nor to congregate where it grows. Thomas Nuttall, the adventuring botanist after whom many local species are named, noted that both pioneers and natives believed “the rattlesnake [will] retire with every mark of trepidation and fear; it would sooner go into the fire than creep over [an ash stick]. A similar superstition . . . prevailed even in the time of Pliny the natural historian.”
References
Plants of the Pacific Northwest Coast. J. Pojar & A. MacKinnon. 1994. Lone Pine Publishing, Redmond, WA.
Grow Your Own Native Landscape. M. Leigh. 1997. Native Plant Salvage Project/WSU Cooperative Extension — Thurston County.
A Natural History of Western Trees. D.C. Peattie. 1953. Bonanza Books, New York, NY.
Winter in the Woods: A Winter Guide to Deciduous Native Plants in Western Washington. E. Guttman & R. Thurman. 1999. Native Plant Salvage Project/WSU Cooperative Extension — Thurston County.
Northwest Trees: Identifying and Understanding the Region’s Native Trees. S.F. Arno & R.P. Hammerly. 1977. The Mountaineers, Seattle, WA.
Plants and Their Names. R. Hyam and R. Pankhurst. 1995. Oxford University Press, New York, NY.
Erica Guttman is the program coordinator of the Native Plant Salvage Project and a Green Pages staff writer. She and Nalini Nadkarni began this column one year ago as a monthly feature to enhance readers’ appreciation of the plants around them. With this issue, Nalini is pursuing other projects and Erica will continue the column solo.