This guy says that 96% of old growth forests in the U.S. have been cut down and 98% of redwoods, the oldest and tallest trees, which can grow ten feet a year. He found the ten biggest stumps, collected clippings, and they have grown hundreds of seedlings from them, which they are planting in Oregon.
I sure thought that Oregon had plenty of trees, but they showed a field with only dead trees, so I guess there is almost always room for more trees.