If they haven't been done yet, there are five distinctive tree types which would be highly appropriate for Mediterranean maps. All of these would be simple, relatively low-poly objects. The only trick is getting the textures right:
Lombardy Poplar (Black Poplar) - these are very common along the edges of fields and rural roads in Italy.
https://upload.wikimedia.org/wikiped...igra-bekes.jpg
A similarly shaped tree is:
Mediterranean Cypress - Maybe just a Lombardy Poplar object with a different texture. These are also commonly found along roads.
http://ericafirpo.com/wp-content/upl...scany-copy.jpg
Olive Tree - fairly common in Italy, rarer in North Africa. (Even better would be a "default" olive orchard texture for some of the "woods".)
http://images.wisegeek.com/olive-tree.jpg
Stone Pine - Another common Mediterranean tree with a distinctive shape. Maybe close enough to the Olive Tree that it could use the same model, but scaled up and with a different texture.
https://upload.wikimedia.org/wikiped...inus_pinea.jpg
Date Palm - Shorter, with a fatter trunk, and bushier foliage than the existing coconut palm tree object. Very common in North Africa, especially around oases. (For North Africa, default "woods" textures might default to date palm plantations.)
http://static1.squarespace.com/stati...35647/pix1.jpg
It would also be very cool if certain road sections on the Italian maps could have auto-generated poplar or cypress trees along them, since until well after WW2, Italian roads were often lined with trees. Many still are. In addition to looking cool, the trees also present a challenge during strafing missions.
http://thumbs.dreamstime.com/x/tusca...y-24446544.jpg