Study: High deer population hurts some native plants

MINNEAPOLIS (AP) — High deer populations in parts of southeastern Minnesota are destroying some native plants, according to University of Minnesota researchers.
“In some areas deer are changing the whole plant community and the tree community, too,” said Lee Frelich, director of the University of Minnesota Center for Hardwood Ecology and one of the authors of the study.
The research, published in the latest edition of Conservation Biology, a national scientific journal, suggests that efforts to preserve natural areas will fail unless white-tailed deer populations are reduced by hunting or other means.
Frelich and graduate student David Augustine conducted experiments at three sites with old-growth trees in Rice and Hennepin counties in 1995 and 1996.
The researchers studied the effects of deer browsing on different varieties of trillium at each location and related the damage to the density of deer in the area. They chose trillium because it is a favorite deer food and a good indicator of forest health.
“If a forest is lush and contains trillium, we know that it’s probably in balance,” Frelich said. But if trillium disappear, he said, it is a warning that the forest understory is changing and that other species could be at risk.
The study found that in two forests where hunting had been banned for more than five years and deer populations were high, the animals removed more than 50 percent of the reproductive trillium each year and the plants that came up the next spring were smaller. Where small protective barriers were put around trillium in the same areas, the plants survived and after two years had bigger leaves and taller stems.
Trillium once thrived in Minnesota, especially in the Big Woods area, a huge forest dominated by elms, sugar maple and basswood that once covered more than 2,000 square miles of south-central Minnesota. All but 2 percent of those forests have been converted to farmland and other uses during the past century.
Repeated overgrazing of the plants eventually will destroy them, Frelich said.
The researchers compared the trillium at two sites with large deer populations to another site that had been hunted periodically and had one-sixth as many deer per acre. They also planted trillium in some areas to see how well it survived deer grazing.
Bob Djupstrom, supervisor of 118 scientific and natural areas managed by the Minnesota Department of Natural Resources, said deer populations are much higher than they have been historically.
To address the problem, public hunting is allowed on all but 20,000 of the state’s 176,000 acres of scientific and natural areas. Special hunts are allowed sometimes on the remaining 20,000 acres.
Ed Boggess, DNR wildlife program manager, said the effects of deer on native plants is an emerging concern.
“We’re definitely trying to balance a whole lot of concerns and values and interests that are out there,” Boggess said.