We harvest the cork out of the trees every ten years but it's absolutely false that the owners of these trees make lots of money like someone here has said in another comment. We just get enough to keep the forest clean of underbrushes. This is a real truth.
Moreover, because his area is very dry in summer we suffer fires that burn the forests every decade or two. Fortunately the burnt cork still works as an insulator, it's black on the outside and therefore can only be used as insulators in buildings. Amazingly, because cork it's such a great insulator burned cork trees survive the fires and develop very easily. You've mostly lost the cork production though...
We had a great fire at the beginning of the past summer that could be even smelt from Barcelona (180Km away from this forest). I have a couple of interesting pictures of the cork trees and how they develop.
This is a picture taken right after the great fire: http://goo.gl/3oM8O
Three months later all trees are developing again, however cork needs to be peeled. We actually lost three years of bark growth because the last harvest was three years ago: http://goo.gl/3ZBHl