Minnesota's great basswood and sugar maple forests have been cut into smaller and smaller pockets during the last 150 years. The "Big Woods" that once ruled the state are long gone, fractured into hundreds of parks and reserves.

There are still remnants of the old forest that have never been logged, or at least haven't been logged in a century. But they're separated from each other by highways, homes and farms, and it's unclear which plants and animals are still able to reproduce and which are on their way to extinction.

Foresters with the University of Minnesota are starting a long-overdue count, aiming to identify each plant in what is left of the Big Woods of south-central Minnesota. During the next two years, they'll find out where some of the rarer plants, such as trilliums, are still living and see if there are ways to bring plant life back.

"We're starting with plants because if the plants go, then pollinators go, and the whole ecosystem goes," said Lee Frelich, director of the U's Center for Forest Ecology. "Think of a city with all these big buildings that are empty of people. You can still have old trees surviving, but with nothing else, it's all degraded."

The Big Woods is what the explorers first called the shady forests dominated by elm, basswood, red oak and sugar maples that once lined the edge of Minnesota's prairies. Before European settlement, the woods covered an estimated 1.3 million acres in what is now the Twin Cities and south-central Minnesota. There are roughly 28,000 acres of it left, or about 2%, Frelich said.

While those remnants have been carefully protected in state parks and science reserves, many species may need more space to regenerate.

Many of the plants rely on insects to pollinate. When the forests are separated from each other by farms and subdivisions, it can be difficult if not impossible for those pollinators to make it from one patch to another, Frelich said.

The major stresses on the forests have also been getting worse over the last few decades, he said.

Invasive earthworms eat up much of the duff and fallen leaves on the forest floor, leaving barer soils with fewer nutrients. High and dense deer populations have ravaged some of the young plants and seedlings before they have a chance to grow. Climate change has made certain pests worse and has caused more floods, which have become more damaging because of the way earthworms have disrupted the soil, Frelich said.

"When you lose that understory of plants, the woods can't function because the nutrients keep washing away," he said. "Without the nutrients the whole system becomes more 'droughty'; even if you don't lose species entirely, they don't grow as tall or as abundantly."

Frelich will be helped by a team of citizen experts from the Minnesota Native Plant Society, who will help locate and document plants. The U has records and seed banks going back 150 years, so researchers should be able to get a fairly accurate sense of which species were around before Europeans arrived.

The research will be funded by the state's Environment & Natural Resources Trust Fund.

The hope is the findings will help forest managers bring certain species back, whether by hand planting seeds, moving pollen from one park to another or hiring sharpshooters to lower deer populations, Frelich said.

"If you want to fix a problem, you have to know what it is," he said.

The findings will be immensely helpful to forest managers around the Twin Cities metro, said John Moriarty, senior manager of wildlife at the Three Rivers Park District.

Three Rivers has kept chunks of the Big Woods alive in place such as Elm Creek, Lake Rebecca, Carver and Baker parks. The park district has been trying to reconnect pockets of forests to each other whenever it is able, Moriarty said.

"Most birds that live in maple or basswood forest can fly between them, but when you think of small mammals, salamanders, frogs and turtles, they can't get from one to another," Moriarty said. "Trillium seeds are moved by ants and ants don't move far. So when you have a road between two chunks of woods, it's a problem."