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Trees: It’s what’s for dinner

July 15, 2008
By Eric Ellis, CRA Biologist, Summer 2008 Catalyst

Emerald Ash Borer and Beech Bark Disease in Northern Michigan

In the past few years Emerald Ash Borer (EAB) and its lesser known counterpart Beech Bark Disease (BBD) have been spreading throughout northern Michigan. In CRA’s 13 county service area, eleven have confirmed EAB infestations; seven have documented cases of BBD. The spread of these two invasive species is causing wholesale changes to the “Up North” landscape we all enjoy.

The Gory Details

Both EAB and BBD are invasive species, but their biology is slightly different. EAB is a small metallic green beetle native to northeast Asia that was first discovered in 2002 near Detroit. It is suspected that the beetles arrived in wooden packing materials from Asia. The adults do very little direct damage to the tree but the larvae eat the growing tissue under the bark girdling the tree and killing it. EAB adults can fly to new trees but the spread of the beetles to northern Michigan has been hastened by people transporting firewood infected with EAB larvae.

BBD has been in the U.S. since 1890 but wasn’t identified in Michigan until 2000. BBD is an intricate cooperation between beech scales, a tree sap feeding insect, and two or more species of fungi. The feeding scales injure beech trees making them susceptible to Nectria fungal infections. Nectria can kill trees outright or weaken them enough that they are snapped in half during storms.

According to www.emeraldashborer.info EAB has killed more than 30 million ash trees in SE Michigan and cost tens of millions of dollars for treatment and removal. BBD is currently most prevalent outside of large populated areas and it is uncertain how many trees have been killed or how much money has been spent on dealing with the problem. What is certain are the negative impacts on northern Michigan’s rivers, wetlands, and upland ecosystems.

Importance of Beech and Ash Trees

Beech and three species of ash are abundant in northern Michigan in a variety of ecosystems. White ash and beech are common associates in fertile upland sites. Red ash (also confusingly known as green ash) is more common along the shores of rivers, streams and lakes. Black ash is mainly found in swamps and wetland areas.
In the absence of other mast trees (especially oaks) beech nuts are the main source of food for many species of wildlife. Beech nuts are eaten by more than 40 species including game and non game birds, deer, small mammals, and bear. The growth patterns of beech make them very valuable as den sites for small mammals and raptor nests. It is safe to say that the loss or reduction of beech in northern forests will dramatically reduce the habitat and food for game and non-game wildlife.

Primarily known for its lumber, ash trees are surprisingly important for wildlife as well. Many species of small mammals and birds feed on the rice-sized seeds that are produced by the millions. These seeds are especially important for wild turkeys which feed on them during the winter as they rest on top of deep snow. In addition to its wildlife benefits black ash is culturally significant to some Native American tribes for its use in basket weaving. Both black and red ash are important riparian and wetland species which stabilize banks, provide habitat for wildlife, filter water, and maintain wetland water levels.

Solutions?

There are no silver bullets for either invasive. Individual trees infected with EAB can be treated with a few select pesticides but treatments are only feasible on a small scale, such as a valuable yard tree. In mid June 2008, Purdue University released a wasp from China which parasitizes EAB. The success of this biological control is uncertain and may be too late for the ash trees of northern Michigan. Individual beech trees can be at least partially protected from BBD by scrubbing away the insects, high pressure water treatment and the use of certain horticultural oils but there are no practical large scale treatments. Private landowners deciding what to do about EAB and BBD in their woodlots and yards should consult a reputable consulting forester or arborist. Treatment options, including selective logging, will depend on the amount of each tree specie on your property and your overall property goals.

The main action we can all take is to maintain species diversity by planting a variety of native trees and shrubs to “replace” the lost food and habitat. Suggested tree species include hackberry, swamp white oak, balsam poplar, yellow birch, black cherry, and any native oak. Good shrub choices include dogwoods, winterberry, elderberry, serviceberry, hawthorns, sumacs, American plum, hazelnut, and crabapples. Plant hardiness zones in CRA’s service area range from 4a-6b. Before planting refer to a reliable source for specific habitat requirements of the species listed or to find other species options. Two great sources include Michigan Trees by Barnes and Wagner and Landscaping with Native Plants of Michigan by Steiner.

How we deal with these invasives now will dictate what the Northwoods will look like for future generations of wildlife and people.


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