Fraxinus latifolia

Oregon ash

Oleaceae

The Basics

Taxonomy: Kingdom - Plantae (plants). Subkingdom - Tracheobionta (vascular plants). Superdivision - Spermatophyta (seed plants). Division - Magnoliophyta (flowering plants). Class - Magnoliopsida (dicotyledons). Subclass - Asteridae. Order - Scrophulariales. Family - Oleaceae (olive). Genus - Fraxinus L. (ash). Species - Fraxinus latifolia Benth (oregon ash).

Ecology: Oregon ash (Fraxinus latifolia) is the only native species of Fraxinus in the Pacific Northwest. It is commonly found in riparian habitats and is not managed for timber production. This tree may reach the age of 250 years and is fast growing the first third of those years, then grows slowly. The seeds are eaten by birds and squirrels. The wood is most used as fuelwood. Although Oregon ash is sometimes found growing as high as 1520 m (5,000 ft) in elevation, it usually does not occur higher than 910 m (3,000 ft). Its preferred habitat is poorly drained, moist bottom land with deep soil rich in humus (fig. 2). In the central Willamette Valley of western Oregon, it is most commonly found on sites with silty clay loams and clays. The species also grows in sandy soils or moist, rocky, gravelly soils. It often follows streams and swamps in ribbonlike fringes and is characteristic in seasonally flooded habitats. Oregon ash is also found on adjacent forest sites at higher elevations, in old fields, and along roads. It grows on Alfisols, Inceptisols, Mollisols, and Ultisols.

Identification

Oregon ash has moderately rapid growth for 60 to 100 years and attains a height of 18 to 24 m (60 to 80 ft) and a d.b.h. of 40 to 75 cm (16 to 30 in) in 100 to 150 years on good sites. Individuals may grow twice as large and reach 200 to 250 years of age under favorable conditions, although they generally grow slowly after their first hundred years.

The most notable use of Oregon ash is for fuel; it splits easily and has high heat value. The symmetrical shape, rapid growth rate, and hardiness of Oregon ash have resulted in its being planted as an ornamental tree and a street tree in cities within its native range, in the Eastern United States, in southwestern British Columbia, and in Europe. It is found in botanical gardens of western and central Europe. The wood of Oregon ash is used in its native range for tool handles, sports equipment, boxes, cooperage, and furniture.

Threats

Oregon ash is attacked by a variety of insects. Thysanocnemis spp. are small weevils that can destroy 60 percent of a seed crop. The heart rot Perenniporia fraxinophilus attacks older trees and may cause extensive cull. The true mistletoe Phoradendron longispicum is found on Oregon ash.

The species is classed as intermediate in tolerance of shade. Individuals self-prune quickly with side shade, and forest-grown trees have long, clean trunks and narrow, short crowns with small branches. Overtopped trees respond well to release. Open-grown trees on moist sites have short trunks and wide, round-topped crowns with large limbs. Oregon ash is often a small, crooked tree on dry sites or at high elevations.

Reproduction

Flowering and Fruiting - Oregon ash is dioecious; its small greenish flowers appear in dense, glabrous panicles with the leaves in April or May. The fruits, oblong to elliptical samaras, ripen in August or September. They are 3 to 5 cm long and 3 to 9 mm wide, including the wing, and are light brown when mature.

Seed Production and Dissemination - Seeds are produced about the 30th year. Oregon ash is an abundant annual seeder in open stands or as isolated trees, but heavy crops occur at 3- to 5-year intervals in forest stands. Most seeds of ash have dormant embryos and require cool, moist stratification to germinate. They have medium to high germination and persistent viability. Germination is best and seedlings are most abundant on moist or wet soils rich in organic matter. Germination is scanty in sandy or gravelly stream bottoms where seeds are carried away by floods.

Seedling Development - Germination is epigeal. Seedlings grow in height rapidly in rich soils and slowly in poor soils. They are somewhat tolerant of shade when quite young. Growth is rapidly checked by drought, but seedlings survive drought well.

Vegetative Reproduction - Sprouts from stumps are common and vigorous.

Species Distribution

Citation

USDA Plant Database
USDA, NRCS. 2016. The PLANTS Database (http://plants.usda.gov, 4 February 2016). National Plant Data Team, Greensboro, NC 27401-4901 USA.

Silvics of North America
Burns, R.M., and B.H. Honkala. 1990. Silvics of North America (Volume 1: Conifers, Volume 2: Hardwoods). USDA Forest Service Agricultural Handbook 654.

Intermountain Herbarium
Consortium of Intermountain Herbaria. 2016. http//:intermountainbiota.org/portal/index.php. Accessed on February 04.

Burke Museum Plant Image Collection
The plant image collection at the Burke Museum, University of Washington.

Jepson Manual
The Jepson Manual: Vascular Plants of California. B.G. Baldwin, D.H. Goldman, D.J. Keil, R. Patterson, T.J. Rosatti, and D.H. Wilken [editors]. 2012. 2nd edition, thoroughly revised and expanded. University of California Press, Berkeley, CA., hardcover; 1600 pages. ISBN-13: 978-0520253124.

USGS Plant Species Range Maps
Critchfield, W.B., and Little, E.L., Jr., 1966, Geographic distribution of the pines of the world: U.S. Department of Agriculture Miscellaneous Publication 991, p. 1-97. Little, E.L., Jr., 1971-1978, Atlas of United States trees, volume 1,3,13,17, conifers and important hardwoods: U.S. Department of Agriculture Miscellaneous Publications.