Using airplanes, satellites, ground surveys, networks of permanent plots, and calls from concerned citizens, Michigan Department of Natural Resources (DNR) forest health specialists, working in cooperation with universities, the U.S. Forest Service and other state agencies, continuously monitor the condition of the state's 19.3 million acres of forest land.

Though public attention has been focused on the infestation of the emerald ash borer, an invasive species from Asia which has killed or damaged approximately 15 million ash trees in the Lower Peninsula, and recently was found in the Upper Peninsula, the DNR tracks a number of other pests and diseases that pose a threat to Michigan's forests.

Jackpine Budworm "Many insect and disease problems occur in cycles," said Roger Mech, a DNR program leader for forest health monitoring based in Lansing. "Some are tied to drought cycles that only surface every decade or so, but some are tied to the ever-changing conditions of the forest."

Well-known examples include Dutch elm disease and chestnut blight, which largely removed the American elm and American chestnut from our forests, and the infamous gypsy moth that defoliated more than three million acres of trees in Michigan between 1984 and 1997, and once again appears to be on an upward trend statewide.

"Understanding the impacts of these exotic pests, including beech bark disease, oak wilt, jack pine budworm and many others, help resource managers make short-term and long-range plans for the sustainable uses of the forest," Mr. Mech said.

Beech bark disease is one of the latest exotic pest problems to plague Michigan forests.

"The discovery of beech bark disease in Michigan in 2000 marked the beginning of a major shift in the ecology of our northern hardwood forests," said Bob Heyd, DNR forest health management program leader in the Upper Peninsula.

The disease, which is caused by beech scale, a sap-feeding insect, and an associated fungus called Nectria, currently threatens Michigan's 7.2 million acres of maple-beech-birch type that includes some 138 million beech trees. More than 10 percent of these trees, those greater than nine-inch diameter, are highly vulnerable to damage.

Like the emerald ash borer, the disease is being spread by people transporting firewood.

The disease was first detected at Ludington State Park in the Lower Peninsula and at a state forest campground in the U.P. Researchers at Michigan State University are developing a model to predict how rapidly beech scale and beech bark disease will spread through Michigan.

In the western Lower Peninsula, for example, the spread of the disease is slower than in the U.P., because of the fragmented nature of the forests in the region and the smaller number of beech trees on the landscape.

Meanwhile, at the USDA Forest Service research facility in Delaware, Ohio, scientists are using trees from Michigan to develop disease-resistant varieties of beech.

"The preliminary data provide the first genetic evidence that resistance is a heritable trait," Mr. Heyd said. "This hopefully will lead to producing disease-resistant beech seedlings used to replace trees lost to the disease."

The long distance moving of firewood also is responsible for the increase in oak wilt in several areas around the Upper Peninsula and the northern Lower Peninsula.

Although oak wilt primarily is spread from diseased tree to healthy tree through the tree's root systems, it also can be carried by insects. Firewood infected with oak wilt is probably the most common way for this disease to be introduced into new areas.

To help slow the overland spread of oak wilt, the DNR suspends tree harvesting activities in state forests between April 15 and July 15, where red oak trees might be left by the loggers.

"The sap-feeding beetles responsible for spreading oak wilt are most active during this period. They pick up spores from diseased trees or oak firewood and transmit them to fresh oak wounds created by homeowner activities such as pruning or to trees damaged by logging operations," Mr. Heyd said.

The jack pine budworm 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 jack pine stands when they reach maturity minimizes budworm-caused tree mortality and reduces the threat of damaging wildfires.

The jack pine budworm epidemic has spread to most jack pine areas of the Upper Peninsula. In 2004, 141,646 acres of jack pine were moderately to heavily defoliated, including young plantations with 50 to 80 percent reduction in total foliage.

"Most of these more vigorously growing younger trees have viable buds remaining on terminal branches and will survive," Mr. Heyd said. "High risk, older jack pine stands defoliated for the second or third consecutive year are being evaluated to determine harvest priorities."

For more information, including links to other agencies and universities that work with the DNR to ensure that forests remain healthy and productive, visit the forest health page on the DNR Web site at www.michigan.gov/dnr.