Cedar Valley Arboretum & Botanic Gardens

Ash Trees in Iowa

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Have you been reading about the emerald ash borer takeover in Iowa?  The little buggers aren’t quite here yet, but many Iowa cities are taking proactive steps now by removing susceptible ash trees that are already weakened from disease or damage.  Beginning the process now will hopefully lessen the infestation as well as redevelop our canopy over time instead of seeing gaping holes in our landscape down the road when all infested ash trees must be removed.

Want to learn more about what Iowa is doing to prepare?  Check out this article in today’s Des Moines Register:  http://www.desmoinesregister.com/article/20110106/NEWS/101060331/Iowa-takes-an-ax-to-ash-trees.

Let’s take a closer look at the ash tree.  Found in the Oleacea family (same family as lilac and the olive tree), the ash tree was planted in parks, along streets and in the home landscape for many years.   The tree became popular as a moderate grower with a handsome shape and several varieties have colorful fall foliage.  The four species that are likely most familiar to Iowans are the White Ash (Fraxinus americana), Black Ash (Fraxinus nigra), Green Ash (Fraxinus pennsylvanica) and Blue Ash (Fraxinus quadrangulata).

Ash trees are easily identified by their leaf shape along with their opposite branch structure.  Many other trees also have a similar compound leaf (like honeylocust, walnut and hickory) but do not have opposite branching.  Opposite branching is when two branches attach at the same spot (called a node) on the stem across from one another.  If you are more of a visual learner (like me!), check out this great bulletin from Michigan State University Extension:  http://www.anr.msu.edu/robertsd/ash/ashtree_id.html.  Scroll down to see photos of the leaf and examples of opposite branch structure.  The bulletin also does an excellent job defining a compound leaf:  “A compound leaf is one that has more than one leaflet while the entire leaf, as defined, has a bud at its stem base (petiole).”  An ash leaf can have up to nine leaflets on one leaf.

Sidenote:  Did you click on the newspaper article and read the sidebars?  The Des Moines Register did a great job providing additional information on the tree distribution in Iowa, tree identification and insect identification but there was one misleading photo.  Click on the “Identifying ash trees” box again and see if you can find what I’m talking about.

The Michigan State University Extension bulletin identified for us opposite branching as well as the makeup of a compound leaf.  The top left photo of the “Identifying ash trees” box points to two leaflets instead more accurately pointing to two whole leaves or branches attached oppositely on a stem.  Gosh, don’t you feel smart now??  🙂

See you in the gardens.


Written by cedarvalleyarboretum

January 6, 2011 at 6:24 pm

Posted in Uncategorized

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