The rapid advance of the Emerald Ash borer has caused many in Michigan to consider alternative trees for landscapes and street trees. Ashes, both green and white, were popular choices for many reasons; there were tolerant of urban conditions, grew fast, had many desirable ornamental characteristics and, until the advent of the Emerald ash borer, had relatively few pest problems. Presently, the future for ashes looks bleak in the areas where the ash borer has been found. To date, there appears to be little natural resistance among our native ashes to this exotic pest. Chemical control may be possible but will likely involve regular and expensive insecticide treatments either through stem-injection, soil drench, or trunk and crown spray.
A typical reaction to this situation is to look for an ‘alternative’ species; some tree that we can plant in place of green ash or white ash. However, to latch on to one, or even a handful of selections, as replacements for ashes, invites us to repeat the mistakes of the past. For those of us who work with the Green Industry and urban forestry, the Emerald Ash Borer crisis is a teachable moment. A recent survey indicated that ashes comprised up to 25% of the street trees in some southeast Michigan cities. In all likelihood the Emerald Ash borer will eventually kill most of these trees. As trees are lost to ash borer, a large-scale re-planting effort is underway. To maintain the long-term health and sustainability of our landscapes and urban forests we need to consider and plant a diversity of species and selections. Ashes were great trees, that’s why we planted so many of them. However, no one tree, or even a handful trees, can fulfill the role of ashes in our landscapes. In order to promote a diversity of selections as homeowners, landscapers, and urban foresters we have developed this guide of Suggested Trees for Michigan’s Lower Peninsula.
In this guide we present suggestions for species that should be considered in situations where a homeowner, landscape, or urban forester may have planted an ash in the past. We have limited the guide to medium to large trees that fulfill similar design intent as ashes. All selections are hardy to at least zone 5, which covers the southern half the Lower Peninsula of Michigan. For each species there is an html page for quick viewing and a printable .pdf file. We present information of general species characteristics, mature form and size, and other noteworthy characteristics. For species that are native, we provide an image of Little’s species range map. Our guide focuses on the species level, though we do mention cultivars of mention species. For more detail on individual cultivars, consult Dirr or the Penn State Street Tree Fact Sheets.
The devastation caused by exotic pests such as Dutch elm disease, chestnut blight, and emerald ash borer has taught us the importance of species diversity in our landscape. Exotic pests can be especially destructive because our native species may not have evolved and resistance mechanisms. A couple of rules of thumbs can help to promote species diversity.
The 10% rule. This rule states a single species should make up no more than 10% of the trees in a particular area. So if an especially destructive pest breaks out, 90% of the trees will remain healthy.
The ‘Look around’ rule. This rule is helpful for homeowners and landscaper working on a smaller scale. This rule states when you select a tree; look around, if you see a lot of a particular species, plant something else.
The Great Debate
In developing a list such as this, there are always trees that some think should have been included but weren’t, or were included but shouldn’t have been. Our goal is to promote diversity and sustainable landscapes. We have tried to present a representative number of selections that represent ‘tried and true’ trees, native trees, and some lesser-known or underused selections that are suitable for Lower Michigan.
Availability: The “death toll” from EAB is staggering and rising everyday. Replacing the trees lost will take years. Nurseries in Michigan and throughout the country are growing trees to meet the demand created by the Emerald Ash Borer. But the production of landscape and street trees is like a pipeline. Producing a 2” or 3” caliper tree takes several years.
If the species and size you want is not available at your local nursery or garden center consider:
A smaller size. If you can’t find a 3” caliper tree, is a 2” tree available?
A different stock type: Trees are sold as container stock, balled in burlap (B & B), and bare root. Container trees are increasingly popular because they are easy to handle and usually transplant well. If the tree you want is not available in a container, check to see if it is available as a B & B tree.
A different species or cultivar. There are many wonderful trees on this list. If the tree you want is not available, consider another selection with similar form and size characteristics.
Sources:
Information presented in this guide has been assimilated form a variety of sources including:
Cornell University Urban Horticulture Institute Recommended Urban Trees for USDA Zone 6 and Below, Nina Bassuk, ed.
Tree and Shrub Gardening for Michigan by Tim Wood and Alison Beck. Lone Pine Publishing, Edmonton, CA. 352 pp.
Trees of Michigan and Upper Great Lakes by Norman Smith. Thunder Bay Press, Lansing MI. 178 pp.
Web development: Sandy Allen
Photo credits: Jesse Saylor, Michigan State University, Department of Horticulture J. Frank Schmidt and Sons Nursery
Illustrations: Marlene Cameron
