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Tips for identifying Ash trees

With the invasive Emerald Ash Borer (EAB) now found in Suffolk, Essex, and Berkshire Counties, many concerned members of the public have asked us for tips on how to identify Ash trees so that they can check them for signs of infestation. Here are some of the key characteristics of Ash:

Green Ash

White Ash

The two most common species of Ash in Massachusetts are Green Ash (Fraxinus pennsylvanica) and White Ash (F. americana). In the fall, Green Ash are distinguishable by the spectacular yellow coloration of their leaves, while White Ash display an orangey-red leaf color. Ash trees are one of the few hardwoods in New England that have compound leaves. Each leaf is comprised of between 5 and 11 toothed, oval leaflets that are paired along the leaf stem, except for the terminal leaflet at the top, which points upward.

Once the leaves have fallen from the trees this autumn, you can still identify Ash using the tree’s branching pattern or bark:

  • Ash is one of the few types of trees in New England with opposite branching (that is, their branches and buds are directly across from one another).

  • While the bark of young ash is smooth, the bark of mature Ash trees has a diamond-shaped pattern, as depicted in the photo below:

A mature Ash tree

  • Boxelder (Acer negundo) is a type of maple that could be confused with Ash because it also has compound leaves and opposite branching. However, Boxelder leaves typically have only 3 to 5 leaflets and the leaflets are usually lobed, not oval.

Boxelder leaves

Fall and winter are good times for checking ash trees for signs of EAB damage because it’s easier to observe the bark of a tree once the leaves have fallen. Visit our previous blog post to learn more about what kind of tree damage you should be on the lookout for!

Photo credits: Urban Horticulture Institute, Cornell University; Dr. David L. Roberts, Michigan State University; Paul Wray, Iowa State University, Bugwood.org; http://www.extension.iastate.edu/forestry/iowa_trees/trees/boxelder.html

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