How to remove trees?

[nitnoid]

My current map didn't include the hospital and I wanted to add it to the map.  I went into the world editor and was able to place it where I wanted, went into the game, reset the chunk and the hospital appeared.  However, many trees poked their way into the poi and evidently took priority and punched holes in the building.  I then went back into the editor, deleted the hospital then cleared the area of all objects including trees.  I then placed a new hospital and saved the map.  Went to the %appdata% folder and deleted the region r.2.3.7g and reloaded my save.  I reloaded the chunk and the hospital was there, but all of the trees were back.  I've even tried going to the editor and just deleting everything in that area, performing the same actions as above and every time, the trees and debris respawn.

 

So this leads me to the topic question.  Even if I start a new game with that map, trees and debris are always there.  Is it possible to delete all of the trees in an area or is this a futile attempt at something that cannot be done?

 

Thanks for any help or ideas.