There is a problem in the settings of some budgets file or other. I've tried Majormagee's solution (clear out the Assets folder except for the Model subfolder), and clearing out the Terraiins folder and copying over the contents of the Terrains folder from MAW v 1.31 - and it works fine. Trees and buildings come back. Try flying out of Heraklion, Crete, and there should be plenty of buildings and trees around the airbase.