1) As far as I understand, the trees are planted to act as barriers, i.e., to force players to go around them, but in many places, it's possible to pass through the trees. The editor has a special mode that shows the traversability of cells (a grid with red cells in the top toolbar).
2) And again, about the forest. The map looks a bit empty. I'm not suggesting overdoing it, but adding a couple of resources in those groves wouldn't hurt.