Most forested land is in the northern part of the state. Many southern Wisconsin forests were cleared for agriculture by the late 1800's. Forests in the north were heavily cut for timber by the early 1900's. Therefore, almost all the mature trees you see today are less than 125 years old. Thousands of acres of pine were planted across the state in the 1930's by the Civilian Conservation Corps.
Deforestation is a big concern.
Unlike some parts of the world, Wisconsin has been gaining forest acreage, not losing. After heavy logging early in the 20th century, much land was burned and converted to agriculture. But, since the 1930's, much marginal crop and pastureland has been planted with trees so the state now has more forestland than at any time since inventories began in 1936. But I see log trucks on the road all the time. This harvesting must be having some effect.