In a way -- almost all of the Northeastern U.S., from Pennsylvania to central Maine, had been cleared, for agriculture or logging or both, by around 1900. Much

In a way -- almost all of the Northeastern U.S., from Pennsylvania to central Maine, had been cleared, for agriculture or logging or both, by around 1900. Much of the area is forested again, through no particularly concerted program that I know of. This is why you'll often encounter stone walls in the middle of the woods -- they were put up at the edge of farm plots and pastures. Once it was no longer economical to log the region on a large scale, logging slowed. Improved transportation and the settling of the Great Plains made it comparatively much less profitable to farm the inferior soils of the Northeast. Furthermore, especially in Pennsylvania, resource extraction turned to oil instead of lumber in the early 20th century. The combination of these factors meant that people stopped cutting trees faster than they grew back, except in densely populated areas.