Until very recently—just two hundred years ago—nearly the entire eastern half of the United States was covered by vast tracts of American chestnut and yellow birch, oak, hemlock and maple, all now collectively called “old-growth” or “primary” forests. Reaching into the Midwest, the forests gave way to more open landscapes—grassy, flower-filled savannas and sun-dappled oak/hickory woodlands—before relinquishing to the prairie-covered plains.