Probably to do with chopping it down at or over the zone boundary.
Not sure if they are trees but yesterday I found an invisible object slap bang in the middle of 979, and I have an old invisible object near me on the border between 904 and 864, had Uriel look into that one a while back but he couldn't find anything, and I know it's old because it's in the exact same place on both the War and Peace servers.
Hello,
There is an invisible "Felled Aspen" , at least on Peace server, in zone 978 Pos X : 10.33 Pos Z : 520.35.
Thanks by anticipation for your help.