As you refer to trees your probably dealing with autogen objects.
ExcBuilder v2-though not specifically designed to remove autogen, creating an 'exclude rectangle' to exclude 'ALL' usually removes autogen.
http://www.newsite.fsdeveloper.com/forum/downloads.php?do=file&id=92If you have ADE9X it has an 'exclude rectangle' tool.
If an 'exclude rectangle' doesn't work, or has undesireable results, then replacing the 'land class' with one that doesn't have autogen will. Either replace entire