The Green Ash (Fraxinus pennsylvanica) is a tough, fast-growing deciduous tree that is one of the most widely distributed ash species in North America, ranging from the Atlantic coast to the Rocky Mountains. Long valued as a street and shade tree for its adaptability to difficult urban conditions, it — like all North American ashes — faces catastrophic mortality from the emerald ash borer, which has killed hundreds of millions of ash trees since its arrival in 2002.
• Reaches 18 to 25 meters tall with a broadly oval to irregular crown
• The most widely distributed ash in North America
• Extremely adaptable to urban conditions, drought, and poor soils
• Severely threatened by the emerald ash borer
• Closely related to White Ash but distinguished by green (not white) undersides of leaves
• Ranges from Nova Scotia and New Brunswick west to Alberta and Montana, south to northern Florida and eastern Texas
• Found at elevations from sea level to approximately 600 meters
• The most widely distributed of all North American ash species
• Common in bottomland forests, floodplains, and along streambanks
• Also found in upland sites, prairie ravines, and disturbed areas
• Described by the German botanist Gotthilf Henry Ernst Muhlenberg in 1793
• The species name "pennsylvanica" refers to Pennsylvania
• Widely planted as a street tree across the northern Great Plains and prairie states
• Has become naturalized in parts of Europe
Bark:
• Gray to gray-brown, developing diamond-shaped ridges similar to White Ash but somewhat less regular
Leaves:
• Opposite, pinnately compound with 7 to 9 (usually 7) leaflets, 15 to 30 cm long overall
• Each leaflet 7 to 12 cm long, lanceolate, with serrate margins
• Medium green above and beneath (distinguishing it from White Ash, which has silvery-white undersides)
• Fall color is yellow, often poor or absent
Fruit:
• Oar-shaped samaras, 2.5 to 5 cm long, with the wing extending well below the seed body
• Hang in dense clusters through winter
Size:
• Typically 18 to 25 meters tall and 40 to 60 cm trunk diameter
• Fast-growing, adding 45 to 75 cm per year
• A dominant tree in bottomland hardwood forests and floodplain communities across the central United States
• One of the most flood-tolerant ash species, surviving extended periods of saturated soil
• Seeds are consumed by wood ducks, bobwhite, wild turkey, cardinals, and small mammals
• Deer browse on twigs and foliage
• Supports numerous Lepidoptera species as a larval food plant
• Provides cavity nesting sites for birds and mammals in mature and declining trees
• The emerald ash borer has caused devastating mortality, particularly in the northern Great Plains where Green Ash was the dominant planted street tree
• Loss of Green Ash from riparian corridors is causing significant erosion and habitat degradation
• The emerald ash borer has killed virtually all mature Green Ash trees in many urban areas
• Particularly devastating in the northern Great Plains, where Green Ash was the most commonly planted street tree
• Some communities have lost their entire urban tree canopy
• Not yet formally assessed by IUCN but considered functionally threatened
• Conservation efforts parallel those for White Ash: seed banking, biological control, and breeding for resistance
• Hardy in USDA zones 2 to 9 — among the hardiest of all ash species
• Extremely adaptable to a wide range of soils including clay, alkaline, saline, and compacted soils
• Highly drought-tolerant and flood-tolerant
• Full sun to partial shade
• Very fast growth rate of 45 to 75 cm per year
• Historically one of the most commonly planted street trees in the Great Plains
• Currently NOT recommended for planting in areas affected by the emerald ash borer
• Existing trees can be protected with annual systemic insecticide treatments
• Seedless male cultivars such as 'Patmore' were widely planted before the borer crisis
• Consider alternative species for new plantings in borer-affected regions
Timber:
• Similar to White Ash wood but generally considered lower grade
• Used for furniture, flooring, containers, and pulpwood
• Marketed as "green ash" or simply "ash" lumber
Ornamental:
• Was one of the most popular street and shade trees in the northern Great Plains
• Valued for its extreme cold hardiness, drought tolerance, and rapid growth
• 'Patmore' was the most widely planted cultivar
Ecological:
• Essential component of bottomland and riparian forests
• Provides critical streambank stabilization
• Loss of Green Ash is causing ecological cascade effects in floodplain ecosystems
Restoration:
• Seed banking efforts are preserving genetic diversity for future restoration once biological controls are established
Anecdote
Before the emerald ash borer arrived, Green Ash was the most commonly planted street tree in many Great Plains cities, comprising up to 30% of the urban tree canopy in some communities. In Fargo, North Dakota, and Winnipeg, Manitoba, the loss of Green Ash trees to the borer has created what arborists call an "urban tree crisis," with thousands of dead trees being removed and entire neighborhoods losing their shade canopy virtually overnight.
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