Bottomland hardwood forests along the Woodland Trail and elsewhere in the refuge are rare forested wetlands in Michigan that provide habitat for migrating birds, reptiles, and amphibians, filter pollutants, reduce flooding by absorbing extra water, and release water during dry periods to help recharge groundwater. Much of the original bottomland hardwood forest was lost to logging, agriculture, and urban development, but the refuge has helped recreate conditions that allow these forests to redevelop. Although early Saginaw settlers were below Michigan's frost free line and did not have the highly prized softwood forests of the logging boom, logs from up north and other places floated down hundreds of miles of rivers into Saginaw, where many sawmills lined the Saginaw River and processed vast amounts of lumber for shipment to cities including Albany and Chicago. The first sawmill in Saginaw was built in 1834, log jams could be enormous, and in 1873 logs clogged the Tittabawassee River for 130 miles. Coal discovered in the Saginaw area in 1850 was not heavily mined until after the lumber industry declined in the 1890's, reached its peak in 1907, and then struggled with water-filled shafts, lower quality coal, and too few experienced miners, leaving only a few mines operating by the early 1930's. Beneath the refuge's Woodland Trail, coal was mined from the Riverside No. 1 and 2 Mines, which extended on both sides of and under the Tittabawassee River, and remnants of that past remain in a shale pile along the trail and an elevated trail segment that once served as a railroad carrying coal to ships at the river. After the eras of river logging and underground coal mining, farming became the area's industry in the 1930's, and after the Shiawassee National Wildlife Refuge bought the land from the Johnson family in 1964, some farming continued into the 1970's before the area became a trail system used for hiking, biking, fishing, cross-country skiing, snowshoeing, and walking.