Description and habitat

Green Ash (Fraxinus pennsylvanica) is a wetland species widely distributed across the Long Point Basin. In optimal conditions, Green Ash can grow a large tree to 25 m or more. It is one of five species of ash in the Long Point Basin – these include White Ash (Fraxinus americana), Blue Ash (Fraxinus quadrangulata), Black Ash (Fraxinus nigra), and Pumpkin Ash (Fraxinus profunda). As a genus, ash trees are distributed widely across the Northern Hemisphere. All ash trees in Ontario have oppositely arranged, pinnately compound leaves.

Green Ash is distinguished from the other ash species by its leaf and bark morphology. The leaves are 15-35 cm in total length, elliptical, with 7-11 leaflets, with serrated leaf margins. Unlike White Ash, the teeth on the leaf margin are typically pointed, not rounded. There is short stalk between each leaflet and the central leaf blade, contrastingly with Black Ash. Leaflets are narrower than those of Black Ash.  Leaves are green on the top, and pale green below. In the autumn, the foliage transforms into a deep yellow – almost never red or burgundy as in White Ash. Flowers appear on female trees in May, which transform into winged seeds called samaras, measuring 3-6 cm long. The wing partially encases the seeds. The bark is greyish brown, with narrow ridges and fissures – creating a more irregular diamond-shaped bark pattern than White Ash or Tuliptree (Liriodendron tulipifera).

Across Ontario, Green Ash is found throughout most of the Great Lakes Region. In the southern half of the area, it is a widespread tree species – a regular component of both swamp and riparian systems. In the northern Great Lakes, green ash is more restricted to streambank hardwood forests. The distribution of Green Ash extends to the southern United States, reaching Northern Florida, and extending west to Texas. In swamps, where it reaches its highest abundance, Green Ash most frequently grows with Silver Maple (Acer saccharinum), Red Maple (Acer rubrum), White Elm (Ulmus americana), Black Tupelo (Nyssa sylvatica), Cottonwood (Populus deltoides), Pumpkin Ash, and in the northern half of its range, Black Ash. It grows with many of the same species in waterlogged riverbank forests, but also with Sycamore (Platanus occidentalis) and Black Willow (Salix nigra). In more well-drained riparian forests and less swampy lowlands, Green Ash can often be found with Black Maple (Acer nigrum), Basswood (Tilia americana), Bitternut Hickory (Carya cordiformis), Shagbark Hickory (Carya ovata), Burr Oak (Quercus macrocarpa), Swamp White Oak (Quercus bicolor), Red Oak (Quercus rubra), Tuliptree and White Ash.

Wildlife importance

The winged seeds of Green Ash are consumed by a wide variety of wildlife, especially small mammals, songbirds, and waterfowl. The twigs are also a valuable food source for white-tailed deer (Odocoileus virginianus). Green Ash is also utilized by dozens of insect species. These include many butterflies and moths, including the Eastern Tiger Swallowtail (Papilio glaucus), Mourning Cloak (Nymphalis antiopa), Viceroy (Limenitis archippus), Great Ash Sphinx Moth (Sphinx chersis), Luna Moth (Actias luna), Ash Leaf Cone Roller Moth (Caloptilia fraxinella), the Banded Ashborer Moth (Neoclytus caprea), and many other species!

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. Ash tree saplings remain abundant in the understories of many forests.

Fun facts

• This tree was widely utilized in horticulture as a shade tree, especially as a replacement for dead White Elm trees, before the arrival of EAB
• Green Ash foliage is typically low in tannins, making it an important food source for tadpoles. The leaves are many other, tannin-rich tree species are toxic to these developing frogs.
• Ash-Tree Bolete (Boletinellus merulioides) fungi are often observed near Green Ash trees; they are facilitated by an aphid that feeds on ash roots.
• Green Ash (and Ontario’s other ash species) have 46 chromosomes. This is the same number as humans.
• Green Ash trees are dioecious, with each individual entirely male (pollen-producing, no fruit) or entirely female (seed-bearing, no pollen).

 

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

Photos by Matthew Palarchio 

 

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