It depends what you mean by "replace". It can be anywhere on the spectrum from an exact clone of each tree, to the same count of trees. You're looking at a narr

It depends what you mean by "replace". It can be anywhere on the spectrum from an exact clone of each tree, to the same count of trees. You're looking at a narrow part of spectrum of the meaning of "replace" where you consider the ecosystems affected by the removal of trees. Another narrow spectrum of the meaning could be restoring the absorption rate of carbon dioxide. I'm pretty sure firing seeds from the air constitutes replacing the rough count of trees.