Changing Ash Habitats and the Wildlife Impact

Fraxinus Fuss

Black ash swamp in Ottertail County, Minnesota
Black ash swamp in Ottertail County, MN. Photo courtesy Tim Whitfeld, MN DNR.

A little green bug has potential to cause quite a bother in Minnesota when it comes to our trees in the genus Fraxinus, or ash trees. This pest, the emerald ash borer (EAB), is an invasive insect from Asia. First discovered in Michigan in 2002, it has caused the death of millions of ash trees in the eastern U. S. and southeastern Canada. In our state, EAB was discovered in 2009 in St. Paul, a year later in Minneapolis and southeastern Minnesota, then in greater Duluth in 2016. With nearly 1 billion green, black and white ash trees in our forests, the products, beauty, and habitat they provide will be greatly affected. Many of them are in nearly pure stands of black ash growing in wetlands. Research is underway to find suitable tree species to replace ash, but death of ash trees and conversion to non-ash forest remains a major concern. So far, no evidence exists of resistance in our ash trees to EAB.

Changing Habitats, Changing Wildlife

Our three ash species have excellent value for wildlife. They are used by an array of critters in the wetlands, floodplains, and moist uplands in which they primarily grow. Young trees provide browse for deer and moose. Mature trees offer feeding sites for woodpeckers, nuthatches, and chickadees, and nesting sites for great blue and green herons, and Cerulean warblers. Older and larger trees provide cavities for fisher, and wood ducks, hooded mergansers, and goldeneyes when near wetlands. Downed decaying trees provide cover for salamanders. These are just a few examples from many.

The amount of ash in our forests will affect the impact on habitat as they die. As habitats change, some wildlife will “win” and some “lose”. Critters tied to a habitat type and structure versus specific tree or plant species, like many birds, will be less affected. They will remain if their needs are met, or move to nearby suitable forest if not. Foraging wildlife will reap the benefits of dying and dead trees that offer added insects and fungi. Cavities nesters will find greater opportunity for hollows. Salamanders will benefit from extra downed trees for cover. Berry eaters will discover greater yields as small shrubs and trees like raspberries, highbush cranberries, Juneberries, and pin cherries are stirred by more sunlight. Migration stopover habitat for songbirds will decline when large contiguous stands of ash die. Wetland forests may experience “swamping”, changing over to wet meadows, alder and wetland habitats used by waterfowl, mink, bitterns, woodcock, turtles and more. For habitats that change greatly, we can “make lemonade from lemons” by enjoying the native wildlife that “win”.

Get Your Ash in Gear

So what’s a family forest landowner with ash trees to do?
• First, burn firewood where you collect or buy it. Don’t be “that guy” that carelessly spreads EAB or other invasive insects.
• Be pro-active in your forest management. Plan for its conversion if most trees are ash. Include ash management in your long term vision and goals for your land (i.e. your stewardship plan) and closely monitor your forest.
• If an ash market exists, harvest using best management practices. Reduce the ash, but don’t eliminate it. Shelterwood and or other selective harvest methods are suggested, especially in wetlands. Leave a scattered mixture of qualities, ages and species of ash for their varying habitat values, and genetic diversity and stock.
• Encourage a diversity of native tree species through planting (such as shade tolerant trees appropriate to the site beneath the ash canopy while it is still unaffected) or natural regeneration (such creating canopy gaps less than 60 feet in diameter) to increase your forest’s resilience, and keep it forested and functioning.
• Avoid treating individual, infested trees such as those in yards or residential areas with insecticides as these chemicals can harm water quality and wildlife including pollinators.
• Of course, don’t plant ash.
• As always, diligently watch for and swiftly control invasive plants and animals.
• Check out the MN DNR Forest Stewardship Program for technical advice and long-range planning, such as development of a stewardship plan.
• Finally, have a positive attitude, and encourage your neighbors and others to do the same.

For More Information

To learn more about EAB’s life cycle, how to identify Minnesota’s black, green and white ash trees and an infestation, and report EAB, see the DNR website and Ash Management Guidelines.

emerald ash borer on penny for scale, next to D-shaped exit hole in ash tree
Photo courtesy Howard Russell, Michigan State University, Bugwood.org
Jodie Provost
Jodie is with the Minnesota Department of Natural Resources Fish & Wildlife – Forest Habitat Team.

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2 Comments

  1. What do we know about the negative effects of the insecticide treatment on individual Ash trees? I live in a small townhome community in Bloomington, and we have had our Ash trees treated by a professional tree company. They injected an insecticide near the base of the trunk. It’s supposed to work for 2 years.

    We thought we were going a good thing by treating and preserving our wonderful Ash.

    1. Mark,
      The MN Department of Agriculture has several guidelines for use of insecticides for ash trees. The primary thing they mention is to not treat trees that have more than 50% of the canopy thinning. They state that common insecticides used to treat EAB are not likely to result in risks to human health or the environment when used appropriately. They also have several recommendations to ensure water quality.