MUNISING - Pictured Rocks National Lakeshore officials said an advancing beech bark disease that has spread across the northeastern United States is now moving quickly across the park, leaving dead and dying beech trees in its wake.
The disease, which includes insect and fungal components, produced its first visible symptoms at Pictured Rocks in 2001 and is expected to eventually claim thousands of trees at the park.
Bruce Leutscher, chief of science and natural resources at Pictured Rocks, said that in the years since first discovery of the symptoms at the national lakeshore, park rangers have been monitoring the progression of the advancing front of the beech bark disease, as well as removing trees presenting falling hazards near park facilities, picnic areas, parking lots and other areas.
Workers remove a tree infested with beech bark disease at Pictured Rock National Lakeshore. The disease was first detected in the Alger County park in 2001 and is quickly spreading. (National Park Service photo)
"The killing front is now quickly spreading from east to west through Pictured Rocks, resulting in a high mortality rate for beech trees," Leutscher said. "With no intervention, this exotic disease complex may functionally remove an important native tree species which is an integral part of the northern hardwood forest type at Pictured Rocks."
The pattern of spread of the beech bark scale insect, followed by occurrence of fungal infection and later tree death, led to a classification in 1972 of the beech bark disease development that is still used today.
Leutscher said the "advancing front" is found in areas recently invaded by beech scale insect, characterized by forests with many large, old trees supporting scattered, sparse building populations of beech scale.
This is followed by the "killing front," where areas are characterized by high populations of beech scale, severe fungal attacks and heavy tree mortality. This is the condition now wildly spreading across Pictured Rocks.
U.S. Forest Service rangers said the killing front arrives one to 19 years after the scale insects.
The "aftermath zone" is located in areas where heavy tree mortality occurred and is now characterized by some residual big trees and many stands of small trees, often of root-sprout origin. Young stems are often defective because of the interactions of beech scale, nectria fungus and another scale insect.
"In forest stands, the disease cannot be controlled at a reasonable cost and a program of timely salvage cuttings is the only way presently known to reduce disease losses," Leutscher said. "National Park Service management options do not include large-scale, whole tree harvesting operations across extensive areas of park lands. The management option available is to address the aftermath forest and retain American beech to the extent possible and practical."
Pictured Rocks facility manager Chris Case said the spread of the beech bark disease has created a tremendous amount of new workload for park staff.
"We have removed dozens of hazard trees from the park's developed areas and trails and we expect this workload to continue for years to come," Case said. "These trees are brittle and dangerous when dead, so we have had to be proactive about removing trees that we know are going to die, before they become too dangerous to remove."
Following NPS policies, infected beech trees in more remote areas will be allowed to fall and replenish soils. Leutscher said as mature beech trees are allowed to effectively disappear from Pictured Rocks' forests, the result will be long-term ecological impacts that may be worsened by simultaneous effects of impending climate change.
Leutscher said accounts from Europe indicate the disease was killing beech trees prior to 1849.
"A scale insect, readily visible on the trees, was considered the cause of death until 1914, when it was learned that a fungus - then identified as Nectria ditissima Tul. - infected trees infested by the scale," Leutscher said.
"Around 1890, the scale was accidentally brought to Nova Scotia. By 1932, the scale and an associated nectria fungus were killing trees throughout the mature beech areas of the Maritime Provinces and in Maine," he said.
The U.S. Department of Agriculture said beech bark disease spread from Maine south and west, reaching Pennsylvania by 1975 and West Virginia by 1990.
Michigan Department of Natural Resources officials said the disease was first found in Michigan in 2000 and state parks and state forest campgrounds were the first areas impacted by the disease. The disease was discovered first at Ludington State Park on the west shore of the Lower Peninsula and at Bass Lake State Forest Campground in the Upper Peninsula.
Both of those park areas were home to abundant large, old beech trees. Trees infected with the disease in these areas began to structurally fail when stressed by high winds, according to a "Managing Beech Bark Disease in Michigan" report by Robert Heyd of the DNR in Marquette.
Most of the places where evidence of the disease has now been documented in Michigan generally include the northwestern portion of the Lower Peninsula and the eastern half of the Upper Peninsula.
Michigan has 7 million acres of forests containing beech trees.
"American beech is the only native species of this genus in North America. It is a slow-growing, common, deciduous tree that attains ages of 300 to 400 years," according to Heyd.
Beech is now confined to the eastern U.S., but once extended as far west as California and before the glacial period, probably flourished over most of North America, Heyd said.
Michigan marks the extreme northern and western edge of the range for American beech.
"Beech is an important nut producer in the northern hardwood type," Heyd wrote. "The distinctive triangular nuts are eaten by people and are an important food for wildlife. Beech mast is palatable to a large variety of birds and mammals, including mice, squirrels, chipmunks, black bear, deer, foxes, ruffed grouse, ducks and blue jays."
The U.S. Forest Service predicts the disease will likely continue to expand its range in the U.S. over the next 50 years. The Forest Service said analysis of current inventory data suggests the disease has already invaded most of the areas with relatively high densities of beech, which is most of the range.
Areas with low densities of beech have yet to be invaded.
Leutscher said the disease is a good example of how an exotic invasive species can permanently alter the ecology of an area.
"This has been a very disheartening process to monitor," Leutscher said. "Our responsibility to the American people is to try to manage parks in such a way that they will remain unimpaired for the enjoyment of future generations. When something like this spreads through the park from outside, it is virtually impossible to meet that mandate."
John Pepin can be reached at 906-228-2500, ext. 206. His email address is firstname.lastname@example.org.