I've seen the same phenomenon in New England. If you stop mowing a field for five years, within twenty you'll have a young wood lot. Clear-cut forest grows ba

I've seen the same phenomenon in New England. If you stop mowing a field for five years, within twenty you'll have a young wood lot. Clear-cut forest grows back even faster - as you said, two-three years of blackberries, then hardwood whips will come back from the seed dormant on the ground or the old stumps, and grow up into harvestable timber again in short order. Unless the logging companies are trying to grow a piece back with something that wouldn't naturally grow, there's rarely a need to replant. I would suppose that in this situation, the landscape is too devastated for the natural process to quickly recolonize the area. With so much open pit/strip mining, the old topsoil is stripped away,so all of that residual seed that would otherwise spring up no longer is present, and the soil present is far less welcoming to any wind-blown or animal-deposited seed.