Home › Oleaceae › Fraxinus › Fraxinus latifolia (Oregon ash)

latifolia – “with broad leaves,” from latus meaning ‘broad’ + folium meaning ‘leaf’

Native range: W. North America

Oregon Ash, Oregon 13

Leaves:

  • opposite
  • pinnately compound with usually 5–7 leaflets
  • leaflets up to 13 cm long

Oregon Ash, Oregon 03

Flowers:

  • dioecious
  • small inconspicuous, yellowish (male) and greenish (female) flowers
  • appear before the leaves, in bunched clusters on the twigs

Oregon Ash, Oregon 16

Fruit:

  • paddle-shaped, 1-seeded, winged fruits (like half of a maple fruit) - 3-5 cm long
  • in large clusters on female trees
  • fruit stalks very fine, almost hairlike
  • begins producing seed at about 30 years of age

Oregon Ash, Oregon 15

Other characteristics:

  • up to 25 m. tall
  • opposite branching, with each pair perpendicular to the pair below
  • bark becomes greyish-brown and fissured with age

Oregon Ash, Oregon 02

Relevant info:

  • moderately rapid growth for 60–100 years and attains a height of 18–24 m. and a dbh. of 40–75 cm in 100–150 years on good sites (~200–250 years under favorable conditions)
  • 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
  • only native Fraxinus species in the PNW

Ecology & Adaptations:

  • native to British Columbia south to California, most common in valleys and along rivers
  • in Washington, west of the Cascades but not on the Olympic Peninsula/Mtns
  • found in deep, fertile, generally moist to wet soil along the coast and prairie areas at low elevations, often near streams or in other areas that are occasionally flooded (e.g., ribbonlike forests along creek/river corridors within Puget Sound prairies)
  • growing as high as 1520 m. (5,000 ft.) in elevation, but usually not higher than 910 m. (3,000 ft.)
  • seed dispersal:
    • many seeds transported by wind and flood waters
    • seedlings commonly establish in the understory of existing riparian forests after floods that deposit silt
  • vegetative reproduction – sprouts from stumps are common and vigorous
  • adapted to wetlands:
    • vegetative reproduction decreases reliance on seed germination (which requires oxygen)
    • lenticels (pores) allow oxygen to be transported from air down to roots
    • shallow roots increase access to oxygen in air
  • shade tolerance:
    • moderate
    • young seedlings will grow in fairly dense shade of mature Oregon ash, black cottonwood, red alder, bigleaf maple, Oregon white oak, and willows
    • however, older individuals self-prune (allow branches to dieback) with side shade
    • forest-grown trees have long, clean trunks and narrow, short crowns with small branches: open-grown trees on moist sites have short trunks and wide, round-topped crowns with large limbs
  • drought tolerance – stops growing and drops leaves under hottest conditions
  • tolerates strong winds – root system is moderately shallow but very fibrous and wide spreading
  • herbivore/pathogen defense – tissues of the members of this genus contain numerous compounds that deter herbivory
  • wildlife:
    • food and habitat for beaver, which also significantly damage the trees
    • deer and elk also browse Oregon ash seedlings and stump sprouts
    • seeds are eaten by birds and squirrels