Ash Tree Identification


Hi my name is Keith Wood. I’m a community forester for the Colorado
State Forest Service. We would like everybody to know about a serious
threat to our urban forests in Colorado called the emerald ash borer, or EAB for short. EAB was found in Boulder, Colorado in the
fall of 2013. Prior to that it was initially found in the
United States in the Detroit, Michigan area in 2002. Only true ash trees in the genus Fraxinus
are at risk from this pest. So this is a serious threat we need to be
aware of. One of the first things that we’d like you
to be aware of is if you have an ash tree or not, and we’re going to show you how to
identify those properly today. Ash trees come in many shapes and sizes. For the most part, they mature into large
shade trees. We have various species of ash trees in Colorado
to be aware of. There are some common varieties that are also
planted in many of our landscapes. This includes varieties of the green ash species
like Patmore green ash, Summit green ash and a tried and true cultivated variety called
Marshall seedless. There are also cultivars from the white ash
species. I’m standing by one here now it’s called an
autumn purple. The autumn purple ash is a very commonly planted
white ash tree in the state of Colorado in our communities and it can turn a very vibrant
shade of purple to burgundy in the fall so it’s very noticeable in the fall. Whereas the green ash trees will turn a more
gold and yellow. To identify if you have an ash tree look for
these following traits: one of the first things to look for is the opposite branching structure
that we find on ash trees. Ash trees have opposite branching meaning
the branches, as they develop, will come out opposite each other whereas other species
have alternate branching where the branches will come out alternating along the stem as
it develops and grows. There are only a couple of tree species that
we’ll find with opposite branches in our landscapes: the ash and the maple. The ash have a compound leaf, generally with
5 to 9 leaflets per leaf. whereas the maple is a simple leaf so it’s
easy to determine an ash tree from a maple when the leaves are on the trees. The other thing to look for is a pattern in
the bark. On mature ash trees we’re going to find a
diamond shaped pattern that develops on both white and green ash trees here whereas on
maple trees we won’t see that pattern in the bark. Another thing to look at, and this when we’re
distinguishing species within the ash group, we’ll have white ash trees with a more broad
leaflet, they will have basically an entire or smooth margin or coarsely toothed margin,
whereas the green ash leaflets will be a little smaller and have a more serrated or toothed
margin. Now that you’ve determined if you have an
ash tree it’s time to make a decision on what you’d like to do with that ash tree going
forward. For more information on how to identify ash
trees and how to manage them moving forward, please go to our website, the Colorado State
Forest Service website (csfs.colostate.edu), or eabcolorado.com.

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3 thoughts on “Ash Tree Identification

  1. I have an ash tree I planted in my SE denver backyard three years ago. At what size should I begin to worry about the beetle? My tree is about five feet tall and the trunk diameter is about the size of a dime.

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