Procedurally generated environment

[britisheddy]

Howdy Everyone,

Does anyone know how Bethesda disables the progen environmental stuff such as trees and rocks in certain locations? I am trying to add an area to Londinion, but it keeps getting covered with items that don't show up in the creation kit, so I can't manually delete them.

Here are some pictures that help illustrate my point.

Any help on this would be great! 

Thanks