> Trees readily plant themselves in areas they are well adapted to.
I am very skeptical if that's true – see formerly forested areas like Iceland, Brazil, etc. It's not easy for a single sapling to grow into a tree, even if the conditions are right. That's why companies like Afforestt exist [0].
Trees don't disperse their seeds an unlimited distance. But, if you look at a map of where they want to plant new trees you will find many trees already in those areas.
Edit, back to your point. Forest fires and other natural events regularly kill off large chunks of trees. They need to be able to grow in those areas in order to survive.
I am very skeptical if that's true – see formerly forested areas like Iceland, Brazil, etc. It's not easy for a single sapling to grow into a tree, even if the conditions are right. That's why companies like Afforestt exist [0].
[0] http://www.afforestt.com/