Depends on whether the trees are Autogen or not. If they are autogen, you can place an invisible dummy object or something else near the center of the tree object. However, there can be patches of autogen vegetation with many trees or whatever, and the relevant point then is the center of that patch. These patches are usually the cause of autogen spilling into areas where it shouldn't.
Since autogen by default does not interfere with static scenery objects, the autogen will disappear.
If the trees are static scenery and you can locate the object placement bgl, you can load it in ADE or SBX and edit them out.
HTH
Mark