Monhegan Forest Threatened by Barberry

Contact: Contact: William Livingston, Dept. of Forest Ecosystem Science, 207-581-2990; Nick Houtman, Dept. of Public Affairs, 207-581-3777

ORONO, Maine — After more than a century of clearing for agriculture, browsing by deer and die-offs related to disease, Monhegan Island’s forest appears to be regenerating with a healthy mix of hardwood and softwoods. That’s the good news contained in a report scheduled to be presented to the Monhegan Island Associates by two University of Maine scientists in a public meeting on August 13.

The bad news is that an invasive non-native plant known as Japanese barberry infests almost 40 percent of the island’s 360 acres of forest, already forming an impenetrable thicket in some areas. “This is the first time in Maine that I’ve seen a forest dominated by barberry. It creates a dense wall of vegetation in the understory. We didn’t expect the barberry to be such a problem,” says Bill Livingston, UMaine professor from Old Town in the Dept. of Forest Ecosystem Science and a co-author of the study.

The barberry is likely to exclude other vegetation, says Livingston, but he and master’s student Rick Dyer of Amherst, Massachusetts were unable to get inside the thickets to determine whether or not young trees or other plants were present.

Monhegan is home to a year-round community of 75, according to the 2000 U.S. Census, and a summer season population. It is located about 9 miles off the mid-Maine coast.

The study by Dyer and Livingston is the first thorough quantitative survey of the island’s forests. It was done at the request of the association to provide an informed view about the future forest. The public is welcome to attend the presentation that is scheduled to start at 8 p.m. in the island schoolhouse.

As part of their study, Dyer and Livingston looked at land use changes over the past two hundred years. Starting in the early 19th century, parts of the island were cleared for agriculture. By 1910, much of that farmland had been abandoned.

To evaluate the current status of the island’s forest, the researchers created 63 circular plots randomly distributed in the forest and counted and cataloged all the tree species over 10 centimeters in diameter at breast height within each plot. A more detailed vegetation survey was done on smaller areas within each plot. The researchers focused on areas that have been continuously forested as well as areas where farm fields were abandoned.

The abandonment of fields on Monhegan created an opportunity for white spruce to regenerate in pure stands. Unfortunately, these stands are extremely vulnerable to a parasitic plant, dwarf mistletoe, which has killed most of the white spruce over the last 20 years. Dwarf mistletoe is not the same plant used in holiday decorations. The mistletoe kills by sapping a tree’s strength. Infected trees have a characteristic “witches broom” growth on the branches.

Historically, Monhegan has been dominated by red spruce which is less vulnerable to mistletoe. “Red spruce does exceptionally well in a marine climate,” says Livingston. “Thousands of years ago, when the climate was warmer and pine was more dominant on the mainland, the islands provided a refuge for red spruce.”

While white spruce sprang up quickly in abandoned farm fields, red spruce has continued to thrive in continuously forested parts of the island. Today, red spruce is regenerating along with maple, mountain ash, and other hardwoods in areas formerly dominated by white spruce.

“A lot of the white spruce has died. Most of it has been cut and chipped to reduce the fire hazard,” says Livingston. “The forest that is regenerating will have a good mix of species and should be less vulnerable to pests.”

The barberry problem, however, presents island residents with another problem. A few years ago, a large deer population on the island fed on most vegetation but left the thorny plant alone, giving barberry a competitive advantage over other plants. Even though the Monhegan Island deer herd was removed a few years ago, the barberry continues to have a stranglehold in many areas. “Deer are not the only reason that barberry tends to take over,” says Livingston. “It’s more complicated than that. The barberry will probably have to be physically removed.”

Livingston plans to continue studying the barberry problem in order to advise the island association.