Trees are all fixed... and the pit type deal wouldn't have worked the way you were going about it ..
fixed it the way I would have done it, should work for all intents and purposes and still allows for the hole in the middle ...
if it didn't have the depression in the center then a standard geo LOD would have sufficed, but when doing convex hull on the object.. it kept wanting to fill the top over solid..
Geo LOD was left on pit object as it serves as fire geometry...
BTW... I noticed that nothing was Tagged.... :-\
There is a very good likelyhood that others will make palmtrees and such, so I would suggest registering an Addon TAG here:
http://www.ofpec.com/tags_register.phpor if you're building this for a Mod... use their TAG
It goes a long way towards keeping things from clashing or overwriting one another