Do trees grow into forests?
Yes. If you place a clump of trees and fast-forward time (say 30-50 years) you will see the clump grow out and become a forest. Trees grow faster if they have adequate moisture and are on reasonable altitude. Density also affects how fast (or if at all) a clump of trees will grow. The denser they are, the more chance they have at propogating. Less dense clumps of trees will die over time.