Obstacles in Resource Bases can also be cleared, either by you (when you control the base) or by your opponent (when he/she controls the base).
Some Obstacles can only be removed after reaching a minimum Headquarters level.
Different types of obstacles produce different amounts of Resources when cleared. The greater the amount, the greater the Gold cost.
The greater the amount of Gold an obstacle costs to remove, the less Resources you will get per Gold. Basically, the cheapest obstacles give you the best value.
Obstacles do not respawn on Resource Bases, but trees will respawn randomly on your home base.
Every 13 hours, there is a 40% chance that a new tree will spawn on your home base.
Only the types of trees that you can currently clear have a chance to respawn. For example, the Mangrove Grove won't respawn if your HQ is at level 12 or below.
The maximum amount of trees that you can have on your home base is 60.
When a defense is placed behind a tree, the tree will become translucent. However, non-defensive buildings will not cause a tree to become translucent.
Troops or a Flare going behind a tree will cause it to become translucent as well.
Hiding non-defensive buildings behind trees may be a good idea because attackers may not notice them or destroy them which prevents them from getting Gunboat energy.
Leaving a Mangrove Grove or Mangrove Thicket on your home base and your Resource Bases can be a good idea, as you can hide your Headquarters or Outpost behind them, and if your enemies can't see your Headquarters they may not attack you!
Note that if your base appears to an attacker as an ice island, the trees will be much less effective at hiding structures. There is currently no way to tell if you have appeared as an ice island, however.