I think of trees as representing anti-tank mines that I know are there. The defensive areas near towns would probably have been mined anyway. Another idea could be, trees cause no explosions, but there are mine fields where you either hit one or you don't. Maybe have an M3 that deploys mine laying troops, who scatter and plant mines around the town. You choose the pattern in which these mines are deployed, i.e. random, straight line, zig zag, etc. Mines could have a 30 minute life span, and would be visible to friendlies by a small red glowing dot on the ground. Mine fields would show up to nme as a more generalized glowing area. To counteract the mines, bring along an M3 with troops who either locate and disarm them (up to ten mines in an area equivalent to resup capability), or capture the town...but not both. Could use a key command to direct the troops' action. Just a thought.
Les