Barberry threatens Monhegan's forest

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. At the same time, a University of Maine forest ecology professor told a recent island meeting, 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.

"We didn't expect the barberry to be such a problem," said Bill Livingston, a co-author of a study of the island's forest problems.

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

The study by Dyer and Livingston is the first thorough quantitative survey of the island's forests. It was done at the request of Monhegan Associates to provide an informed view about the future forest.

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.

Historically, Monhegan has been dominated by red spruce, which is less vulnerable to mistletoe.

The barberry problem, however, presents island residents with different 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."