Thanks for the info Discoseven. I had tried exporting a tree I modeled with the "full-detail Mesh" box checked, first as an .obj, then as several other file formats without success. I would get the trunk and main braches to export, but no side branches or leaves.      After reading your reply, I decided to try exporting some of the preset trees and Viola, no problem!  Apparently my tree is either too complex ( too many leaves) or has some other setting that Carrara's export module doesn't like. The default aspen is a fairly simple tree, but even still it weighs-in at a little over 15mb. with the .mat file when exported as an .obj file.  No real complaints here. I am happy that I can model quite complex trees in Carrara and then replicate them by the thousands with no problems within Carrara itself. Why would i even want to go elsewhere,lol?  I used Patrick210's freebie tree shader on this "unexportable" tree in the pic.