1997 Forest Health Highlights - Michigan

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The Resource

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 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.

Special Issues

Gypsy moth, introduced over a century ago from Europe, causes defoliation across the

northeastern United States each year. Until 1997, gypsy moth populations in Michigan had

declined dramatically since 1992 when defoliation exceeded three-quarters of a million

acres. This decrease was largely due to the fungus Entomophaga maimaiga, a particularly

effective natural enemy of the gypsy moth. This fungus was introduced into the state in the

early 1990’s, when gypsy moth populations were at an all-time high. The fungus spread

quickly, and is now established in nearly all counties that have experienced gypsy moth

defoliation. The fungus, which is harmless to other wildlife and the environment, is a

powerful natural control, but it’s effectiveness depends on weather conditions. Warm, wet

weather favors the spread of the fungus, which infects caterpillars as they move across the

ground in search of food. Recent cool, dry spring weather is blamed for a resurgence in

gypsy moth defoliation. Defoliation increased from 3300 acres in 1996 to 38,000 acres in

1997. Fortunately, Entomophaga can remain dormant in the soil for several years until

weather conditions are favorable.

No gypsy moth caterpillars or defoliation

were detected in the Upper Peninsula in

1997. The Michigan Department of Natural

Resources continues to cooperate with the

USDA Forest Service, Michigan State

University Extension, and the Michigan

Department of Agriculture in a Slow-theSpread of gypsy moth project in the Upper

Peninsula. About 4,000 pheromone traps
1997 Forest Health Highlights - Michigan

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were placed in the 3,400 square mile Slowthe-Spread area of the Central Upper

Peninsula. A significant increase in moth

catch throughout the STS zone in 1997 is

currently being evaluated. A significant

proportion of these moths may be blowing

in from nearby infested areas of Wisconsin.

Regional Surveys

Forest Health Monitoring. In 1994, permanent plots were established to monitor the

health of Michigan’s forests. This is part of a nationwide Forest Health Monitoring

Program, in partnership with the Environmental Protection Agency. The motivation to

begin monitoring the health of forested ecosystems grew out of the concern for the

potential effects of air pollutants, insects, diseases, and other stressors, and concern for the

potential effects of global climate changes. There are 247 plots in Michigan, of which 133

are forested.

A second plot monitoring system, the Michigan Impact Monitoring System, provides a

more detailed look at stressors affecting the major forest types in the Upper and northern

Lower Peninsulas. Over 600 plots are measured each summer to determine the health of

mature trees and young seedlings and saplings in the understory of Michigan’s oak, aspen,

and northern hardwood forests.

Recently, information collected from these two plot systems detected a problem with

basswood across much of it’s range. Repeated attacks by a group of insect defoliators may

be one factor contributing to the decline and death of basswood trees. A cooperative effort

between the U.S. Forest Service and several Lake State agencies will try to unravel the

causes and affects of this decline.

Other Issues

Numbers of the jack pine budworm, a needle feeding caterpillar that attacks jack pine of

all sizes, have increased sharply since 1996. Some 25,000 acres were defoliated by the

budworm in the northcentral Lower Peninsula in 1997. Jack pine that is 60 years of age or

older is particularly susceptible to topkill and death. Stands of jack pine that are under

stress from competition caused by poor growing conditions are also prone to mortality

following defoliation. Management efforts focus on identifying high-risk stands for harvest

prior to defoliation, and prompt salvage of trees killed by the budworm. Use of insecticides

is rarely cost-effective against the budworm except in areas, where dead trees may

decrease recreational value. Exotic Forest Pests Other Than Gypsy Moth

The pine shoot beetle (Tomicus piniperda (L.)) was first discovered in two Upper

Peninsula counties in 1997. These counties are included in a quarantine with 63 counties in

Lower Michigan. Although Scots pine is a preferred host, other pines are attacked.

Attacked shoots usually bend and break at the point of attack.
1997 Forest Health Highlights - Michigan

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Tomicus is an exotic pest discovered in Ohio in 1992. It has now been found in Michigan,

Indiana, Ohio, New York, Illinois, and Pennsylvania. A quarantine is in place to hinder its

spread to new areas as evaluations of its environmental and economic impact determine the

next course of action.

The impacts of exotic weeds are not well understood, but the threats are real. Native plants

and habitat in wetlands are being displaced by purple loosestrife (Lythrum salicaria & L.

virgatum). Loosestrife is an aggressive invader, excluding native vegetation where it

grows. Purple loosestrife is not a food source for native animals or insects.

Spotted knapweed (Centaurea maculosa) is an aggressive invader of disturbed sites and

releases chemicals in the soil that affect growth of nearby vegetation. It is a prolific seeder.

It is not eaten by animals because it can irritate their mouths. Knapweed is a poor soil

stabilizer on disturbed sites due to bare ground under plants via alleliopathic exclusion of

other plants.

Other examples of exotic weeds of concern in Michigan include leafy spurge (Euphorbia

esula) and garlic mustard (Alliaria officinalis). Exotic 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. Thus, native flora are competitively displaced, disturbing

natural floral, faunal and ecosystem functions.

For more information contact:

Gerald Thiede, 

State Forester 

P.O. Box 30028 

Lansing, MI 48904 

(517) 373-1275

Forest Health Protection 

Northeastern Area 

USDA Forest Service 

1992 Folwell Avenue 

St. Paul, MN 55108 

(612) 649-5261

February 1997.......

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