Easy way to add trees after expanding the map

[Rodrico Stak]

Pretty much what the title says.  I know that the game won't automatically add trees when expanding the map the way it will with cities, but I'd like to fix the bareness that results without having to either use the public player to distribute trees one tile at a time or in dense, rectangular forests.  Is there any way to do so, or should I get to painting with the tree tool?

Edit: Pak128 if it maters.

[An_dz]

The forest tools does not build a rectangular forest, it creates an elliptical forest, just like all other forests generated in-game.