Major Forest Types

Of Michigan

Forests comprise 53% of the land area of the state, or about 19.3 million acres. These 

forests are a critical component of Michigan’s environment and economy for the 

recreational opportunities and the products they provide. Forestry related industries and 

manufacturing employ 150,000 people statewide and annually contribute $9 billion to 

the state’s economy. Additionally, forest-based tourism and recreation support 50,000 

jobs and add $3 billion to Michigan’s economy. Michigan’s forests contribute to clean 

air, water, and reduce soil erosion. % of Total 

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25 

20 

15 

10 

5 

0 

Maple-Birch 

Aspen-Birch 

Elm-Ash-Soft-Maple 

Oak-Hickory 

Red and White Pine 

Northern White-Cedar 

Jack Pine 

Black Spruce 

Balsam Fir-White Spruce 

Tamarack 

Eastern Redcedar 

The introduction of exotic organisms is the most serious health threat to our native forest 

ecosystems. State and federal agencies are preparing contingency responses and 

increasing resistance to the possible introduction of exotics such as the Asian longhorned 

beetle, the Hemlock Woolly Adelgid, the Balsam Woolly Adelgid, and Sudden Oak 

Death. 

Add the emerald ash borer to a rapidly-growing list of 

exotic pests that have worked their way into the 

Michigan landscape. This small, green metallic beetle, 

previously unknown to North American forests, is killing 

ash trees throughout southeast Michigan, as well as 

Toledo, Ohio and Windsor, Canada. 

The emerald ash borer (Agrilis planipennis) has so far 

killed hundreds of thousands of ash trees in Wayne, 

Oakland, Macomb, Monroe, Washtenaw and St. Clair 

and Livingston Counties, where specialists from 
universities and from local, state and federal agencies are working to identify the extent 

of the infestation and to devise a strategy aimed at slowing the spread of the insect. 

Native to China, Korea, Japan and the Russian Far East, the emerald ash borer likely 

found its way to Michigan hidden in wooden crating or other shipping material. 

Evidence suggests that the insect has been active in the state since at least 1997. 

Symptoms and Signs. Larvae of the emerald ash borer feed below the bark in the 

phloem and outer sapwood, producing galleries that eventually girdle branches and 

entire trees. Half the branches of infested trees may die after one year, and trees are 

often killed within two to three years of the initial attack. 

All varieties of ash trees appear susceptible, including white ash, green ash and black 

ash, as well as several horticultural varieties. 

Adult beetles lay eggs on the bark of ash trees in mid-summer. 

Larvae emerge from the eggs and chew through the bark, where 

they begin feeding on the cambium. After overwintering as fullgrown larvae, the adults emerge from infested trees beginning in 

May the following year. 

Adult beetles form characteristic Dshaped holes in the bark as they chew 

their way out of the tree. 

Declining trees can develop epicormic 

(trunk) sprouts, and dense root 

sprouting may occur when trees die. 

Like its native cousins the bronze birch borer and the two-lined chestnut borer, stress 

brought on by drought and soil compaction probably set trees up for attack by emerald 

ash borer. 

But the insect attacks and kills apparently healthy trees, too, including trees that have 

been fertilized and irrigated regularly. 

Fighting Back. The Emerald Ash Borer Invasive Species Response Team, a multi-agency 

task force formed this summer, is responding on several fronts. Led by representatives 

from the Michigan Department of Agriculture, MDNR, USDA Forest Service and Animal 

Plant Health Inspection Service, Michigan State University and Michigan Technological 

University, the team is developing an integrated emerald ash borer management plan 

that includes: 

• Quarantine enforcement 

• Detection and evaluation monitoring 

• Information and public outreach 

• Emerald ash borer population management 

• Research and development 

A Hemlock Woolly Adelgid quarantine continues to 

restrict movement of eastern hemlock into Michigan 

from infested counties of other states. All eastern 

hemlock shipments require a phytosanitary certificate. 

This follows the interception of the insect at two 

Michigan nurseries in 2000. A rapid early detection 

survey for the adelgid was conducted statewide in 

hemlock stands and in areas adjacent to nurseries in 

2002. No hemlock woolly adelgids were found. 

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Beech bark disease (BBD) was detected in the spring of 2000 and is established in the 

western Lower Peninsula and in the eastern Upper Peninsula. 

The interaction of an exotic scale insect (Cryptococcus 

fagisuga) and a native and exotic canker-causing fungus 

(Nectria sp.) cause beech bark disease. Once infected by 

the fungus, trees usually decline and trunks may break at 

canker sites. The Michigan Beech Bark Disease Monitoring 

and Impact Analysis System was begun in 2001 to: 

• Delineate the advancing & killing front of the scale 

• Identify & quantify tree, stand & site factors influencing 

rates of decline 

• Identify potentially resistant trees 

• Measure impacts of native & exotic Nectria 

• Study regeneration of beech & other tree species 

• Evaluate wildlife impacts 

• Revise beech productivity models to ensure the affected forest resource is 

sustainably managed. 

Findings in 2002 include: 

• Decreased tree vigor in plots with higher scale infestations 

• Increased dead beech in plots with higher scale infestations 

• Higher scale densities in stands with higher number of beech trees 

• Reduced radial wood growth in infested stands 

• Beech regeneration is primarily seed origin 

• Denser beech regeneration in the Upper Peninsula versus the Lower Peninsula 

We continue to cooperate with the USDA Forest Service Northeastern Research Station 

in Delaware, Ohio to identify mechanisms of beech bark disease resistance and produce 

resistant seed and seedlings. 

Sudden Oak Death (SOD) poses a potential threat to Michigan's forest resources. This 

pathogen has killed thousands of oaks, and caused disease symptoms in many other 

tree and shrub species in California and Oregon since 1995. A copy of this report is 

available upon request. The Forest Health, Inventory and Monitoring Program is 

educating Forest Resource and Parks managers, and has taken the lead in a national 

SOD risk assessment effort. For more information visit http://www.suddenoakdeath.org 

In the past decade Sphaeropsis (Sphaeropsis sapinea) has been increasingly associated 

with damage and mortality of red and jack pine in Michigan. Prior to the 1980s, damage 

by the pathogen was rare in the Lake States. Increasing damage by the pathogen has 

been correlated to the increasing prevalence of a more virulent and more aggressive 

form called Type A. Severe damage is often associated with site stresses, and drought 

years. Questions to answer: 1) Are there susceptible and non-susceptible sites? 2) If 

susceptibility is site related, what are the risk factors? 3) At what frequency do 

predisposing stresses occur on susceptible sites? Answers provided by current research 

efforts will likely result in for red and jack pine sustainable yields. 

The Eastern Larch Beetle, Dendroctonus simplex, is epidemic in several areas of the 

Eastern and the South Central Upper Peninsula. This bark beetle is killing tamarack (Larix 

laricina) in stands ranging in size from a cluster of a few trees to stands of100 acres. 

Because infested trees often enter the fall with apparently healthy crowns, mortality is 

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often overlooked until trees fail to leaf out the following spring. Upon closer inspection, 

these "green" trees are completely girdled with beetle galleries. Both native tamarack 

and exotic larch species are susceptible to this beetle. Apparently healthy trees can be 

attacked and killed by the bark beetle. However, 

many infestations are associated with stressed trees. 

Stresses from the drought of 2000-2001 and repeated 

defoliation by the larch casebearer (Coleophora 

laricella) are likely predisposing factors contributing to 

the current epidemic. The larch casebearer is an 

exotic insect introduced to the Lake States in the early 

1900’s. It derives its name from the “case” it constructs 

from a mined-out needle. Defoliation for two or more consecutive years can cause tree 

decline and mortality. Populations generally collapse after a single year of damage 

thanks to two parasites imported from Europe. 

Exotic invasive plants have the advantage of not being limited in growth or reproductive 

potential by biological controls such as insects feeding on leaves, roots, flowers or seeds. 

This gives them a very strong competitive advantage over native flora which are limited 

by these forces due to many years of co-evolution. Thus, native floras are competitively 

displaced, disturbing natural flora, fauna and ecosystem functions. One exotic invasive 

plant receiving much attention in Michigan and the nation is garlic mustard (Alliaria 

petiolata). The Michigan Invasive Plant Council (MIPC) and the Michigan DNR are 

pursuing a broad-based strategy for managing garlic mustard. Conventional control 

strategies are effective if introductions are small and caught early via effective 

monitoring. However, we have many heavily infested areas in the Southern Lower 

Peninsula for which biocontrol currently offer our only real hope. So, a critical part of our 

statewide strategy is exploring the safe and effective use of the biological control agents 

to be offered by Blossey and Nuzzo, Cornell University, New York. 

Incidence of the vascular disease oak wilt continues to increase 

from 2001 levels in several areas around the Upper Peninsula and 

the northern Lower Peninsula of Michigan. 

To slow the overland spread of oak wilt, 

harvesting restrictions are being exercised on 

state land. Forest stands with oak trees are not 

being cut between April 15 and July 15 in areas 

where the risk of oak wilt is high. These dates 

mark the period when the sap-feeding beetles 

responsible for spreading oak wilt are most active. These small (1/4-inch 

long) beetles are attracted to fresh tree wounds and transmit spores to 

oak trees that have been damaged during logging operations.

 Other Michigan Forest Health Issues 

Gypsy moth (Lymantria dispar) populations have begun an upward trend statewide. This 

follows a long period of population decline that began in the early 1990’s and 

culminated in 2001 when, for the first time in over a decade aerial surveys detected no 

defoliation in the state. Since then, egg mass numbers have been increasing steadily 

and defoliation is expected to be locally heavy in some northern Lower Peninsula 

counties. 

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The Jack pine budworm (Choristoneura pinus pinus) is 

considered the most significant pest of jack pine. 

Stands older than 45 years that are growing on very 

sandy sites and suffering from drought or other 

stresses are very vulnerable to damage. Tree mortality 

and top kill resulting from budworm defoliation 

creates fuel for intense wildfires. Harvesting and other 

management activities can avoid budworm caused 

tree mortality and reduce the threat of damaging wildfires while providing suitable 

conditions for jack pine regeneration. A buildup of jack pine budworm populations 

began in the Eastern UP in 2000. In 2002, 105,000 acres of jack pine were moderately to 

heavily defoliated. An additional 130,000 acres were partially affected forest with a 

component of jack pine. This epidemic will spread 

westward affecting most of the UP jack pine resource in 

the next 3-4 years. 

In the Lower Peninsula, jack pine budworm numbers have 

declined from 2001 levels. This is likely the tail end of an 

outbreak that began in 1997. Stands that were defoliated 

previously and show signs of heavy population buildup are 

at risk of mortality. These stands will be harvested. 

Chemical treatment of jack pine budworm infestations is 

rarely cost-effective. 

The Forest Tent Caterpillar (FTC) (Malacosoma disstria) 

defoliated 1.3 million acres in 2002. A little more than 

half of these acres were partially affected stands with 

a component of susceptible trees species. The FTC is 

a native leaf-feeding caterpillar. FTC prefers to eat 

aspen and oak leaves in the UP though it also readily 

consumes paper birch, green and white ash, 

basswood and willow leaves. Sugar maple is readily 

consumed only in the Northern Lower Peninsula. Epidemics occur about every 10-15 

years in the Great Lakes region, and last for 2-4 years. FTC can defoliate trees for several 

years with little ill effect. This is especially true for years with average or above average 

rainfall. Parasites were abundant in this year's populations, signaling a likely significant 

population reduction in these areas next year. 

The Red-Headed Pine Sawfly (Neodiprion lecontei) is an important defoliator of young 

red and jack pines. Heaviest infestations are in pines growing under stress, particularly 

those at the edges of hardwood forests, on poor soils, and where there is heavy 

competitive vegetation. In general, it infests and damages trees less than 15 feet tall. 

Moderate to heavy defoliation stunts height growth of infested trees and forking may 

result from top kill. Complete defoliation usually kills the tree. Building sawfly populations 

were detected in many areas of the Eastern UP and the Northern Lower Peninsula in 

2002. Early detection and suppression of damaging populations is needed to protect 

high value resources. 

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