Description and habitat

White Ash (Fraxinus americana) is one of Long Point’s most ecologically important tree species. Mature White Ash are large trees, over 35 m tall on fertile soils. It is one of five species of ash in the Long Point Basin – these include Green Ash (Fraxinus pennsylvanica), Blue Ash (Fraxinus quadrangulata), Black Ash (Fraxinus nigra), and Pumpkin Ash (Fraxinus profunda). As a genus, ash trees occur across the Northern Hemisphere. All ash trees in Ontario have oppositely arranged, pinnately compound leaves.

White Ash is distinguished from the other ash species by habitat preferences, leaf and bark morphology. The leaves are 20-30 cm in total length, with 5-9 leaflets, which have rounded teeth on the leaf margins. The top of the leaves are deep green, while the underside is pale-green. Autumn foliage is typically burgundy, scarlet or deep orange – making White Ash one of Ontario’s more showy trees in October. Flowers appear on female trees in May, which transform into winged seeds 3-5 cm long. The bark is comprised of intersecting ridges that create a diamond-shaped pattern on the bark. It is very similar to that of Tuliptree (Liriodendron tulipifera) – a species with a very similar ecological niche as White Ash. These two species often co-occur in the same habitats. To tell the difference, Tuliptree has slightly more flattened ridges on the bark, which are more brown than grey than White Ash. However, the two species are very easy to distinguish when the foliage is visible in the summer.

Across Ontario, White Ash is found throughout most of the Great Lakes Region – except for the northernmost areas of Lake Superior. It is a  common tree in many areas, though it is most abundant in the regions south of the Canadian Shield, such as the Long Point Basin. Across North America, White Ash occurs across the eastern deciduous forest southwards into Florida and Texas. In the Great Lakes Region, White Ash is most common in moist forests, such as those dominated by Sugar Maple (Acer saccharum), and Beech (Fagus grandifolia). In these associations, it also grows with Tuliptree, Basswood (Tilia americana), Red Maple (Acer rubrum), Yellow Birch (Betula lutea), Red Oak (Quercus rubra), Bitternut Hickory (Carya cordiformis), and Shagbark Hickory (Carya ovata). It is an adaptable species, being found along swamp margins, and riparian forests, where it occurs with Black Maple (Acer nigrum), Hackberry (Celtis occidentalis), Basswood, oaks, hickories, and other ash species.

Wildlife importance

White Ash is widely utilized by wildlife, especially as a nesting location for songbirds, and as a food resource for many species through it’s seeds. The leaves are a host plant for the Eastern Tiger Swallowtail Butterfly (Papilio glaucus), one of Long Point’s most beautiful butterflies! White Ash foliage also supports the larvae of Mourning Cloak Butterfly (Nymphalis antiopa), Ash Leaf Cone Roller Moth (Caloptilia fraxinella), Polyphemus moth (Antheraea polyphemus), and Cecropia Moth (Hyalophora cecropia) – the latter two species being giant silk moths in the Saturniidae family.

Emerald Ash Borer 

Since the early 2000s, Ontario’s ash species are threatened by an invasive beetle from northeast Asia, Emerald Ash Borer (Agrilus planipennis, subsequently EAB). Originally introduced to Detroit and Windsor on shipping cargo, it has since spread across the Great Lakes Region. In the Lake Erie Region, EAB has killed over 85% of mature Ash trees. White Ash has slightly more resistance than Green Ash or Black Ash, and in some of the woodlots, there are healthy ash trees that have survived EAB. Several insect parasitoids have been introduced in an attempt to control EAB populations. This includes four wasps – Tetrastichus planipennisi, Spathius agrili, Spathius galinae, Oobius agrili. Wasp larvae consume the eggs or larave of EAB, resulting in both EAB mortality and large population increases of the biocontrol waps. In combination with natural predators (including Woodpeckers, Picidae, which can consume >50% of all EAB larvae), native parasitoids, and innate host tree resistance EAB, the future goal is to reduce the EAB population so that native ash trees can naturally regenerate into the forest canopy without experiencing EAB-induced mortality.

Fun facts

• White Ash is an adaptable tree species, growing well in both exposed open areas and shady forest understories.
• White Ash trees are known for their high transpiration rates, meaning they draw a considerable amount of water from the soil and release it into the atmosphere. The cycling of water vapour in these forests maintain the high humidity characteristic of the Great Lakes Region and generates rainfall much needed by plants in the summer.
• This species is dioecious – individual White Ash trees are either male or female. Only female trees produce seeds (samaras), while male trees produce pollen. This requires both sexes to be present for successful reproduction.

 

Written by Matthew Palarchio, HBSc in Environmental Sciences, Western University.

Photos by Matthew Palarchio 

 

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