A lot of the planet used to be forested that currently isn't. Many ecosystems have already been changed by removing forests, among other things. We can plant a

A lot of the planet used to be forested that currently isn't. Many ecosystems have already been changed by removing forests, among other things. We can plant a lot of trees before we reach the point that we need to plant forests where none have been before. And some ecosystems definitely could be improved by planting forests. They can halt desertification, for example.