Canadian Forest Service links

Fraxinus americana L. White ash

Pinnately compound leaf with seven petioluled (stalked) pinnae (leafets)

Habitat

White ash occurs as scattered individuals, on richer, moist, but well-drained soils, in mixture with sugar maple, beech, yellow birch, basswood, and butternut, or with some conifers. It tolerates some shade when young, but needs good access to light later if it is to maintain its place in the stand.

Medium sized tree in spring

Form

White ash trees may reach heights of up to 23 m and stem diameters of up to 70 cm. The stem is typically long and straight in stand conditions and it carries a high, narrow, pyramidal crown of upper ascending branches, and lower branch-es that arch outwards and then upwards at their tips. In open conditions, the crown is much deeper, and broadly pyramidal to rounded.

Morphology

Twigs of three ashes; white ash (left), red ash (right), and black ash (center)

The leaves are deciduous, pinnately compound, 15–40 cm long, and borne in pairs, with each pair at right angles to the previous one. Each leaf has five, seven or nine leaflets, with seven being the most common number. The leaflets are stalked, 6–15 cm long, oval to lanceolate, with wavy or slightly toothed margins, and are usually hairless, as are the petiole and rachis. In the fall, white ash foliage frequently becomes purplish, and that makes the trees stand out from others. The leaflets fall separately, rather than whole leaves falling.

Cluster of male flowers at the pollen-shedding stage

The twigs are stout, purplish to dark grey, somewhat shiny, with scattered lenticels that do not protrude from the hairless surface. The buds are dark brown to reddish brown, and closely downy. The terminal bud is blunt, dome shaped but somewhat four sided, with the uppermost pair of lateral buds touching it. The lateral buds are smaller, rounded to round pointed, and each is set in a V-shaped notch in the upper edge of a U-outlined leaf scar that carries a U-shaped line of tiny vein scars.

Female flower clusters shortly after blooming stage

The flowers are borne from lateral buds in oppositely branched, extended clusters, the male ones being more compact in bloom than the female ones. Male and female flower clusters occur on different trees, so it is only on female trees that the flowers go on to produce fruits. The 25- to 40-mm long fruits each have a sausage-shaped seed pocket, near the tip of which extends a flattened, elliptically rounded wing.

The bark is smooth and grey when young. As the bark ages, it becomes finely and evenly furrowed with thin, firm, somewhat rounded, light grey ridges that tend to intersect in diamond patterns.

Notes

Clusters of mature fruits-the wings start near the end

The light brown, ring-porous wood of white ash is heavy, hard, strong, tough, and usually straight grained. It takes bending well. These features make it suitable for snow shoes, sporting goods, tool handles, and furniture, especially where strength is required.

Bark of a stem, 50 cm in diameter

There is no question that ash can be stressed by drought or site conditions, but one of the main factors affecting its continued health is the presence of ash rust (Puccinia sparganioides) whose alternate hosts are the Spartina ssp.—cordgrasses or marram grass—common in coastal salt and freshwater marshes. The rust may build up unnoticed on cordgrass in the vicinity and, in a favorable year, cause serious damage to nearby ash, especially white ash. Spores released from cordgrasses in marshes have been reported to infect ash trees up to 48 km away under favorable conditions. Severely infected ash trees may appear scorched and the infections of the twigs, petioles, and leaves can result in defoliation. Repeated severe infections can cause large branch mortality leading to the death of trees.

Newly expands leaves

Morphological descriptions should be compared with those of the two other ash species, black ash and red ash, as some features are superficially similar. The only other species likely to be encountered with pinnate-ly compound leaves borne oppositely in pairs are the introduced tree species, Manitoba maple (Acer negundo L.), and the two native elderberry shrubs (common elder, Sambucus canadensis L. and red-berried elder, Sambucus pubens Mich.). These species have other features that do not fit at all closely with those of the ash species.