Well, for once I have to disagree with Erlik, and I say this knowing that he is a tree "fanatic" as much as I am.  He may well be right about the tree lab in Carrara Basic,(never tried it) but Carrara5 standard and Pro recently got a major upgrade(March '06) in the treelab which offers huge strides forward as far as realism and customization possibilities. Since the trees are poly-based, I can "prune" branches, bend trunks and export my finished tree to use over, or to share with other people; even those using other 3D apps. In Carrara standard I can even add a displacement map on the tree trunks closest to the camera to get true 3D bark. The new wind animation feature is terrific as well, and IMO looks more realistic than Vue Infinite's implementation. Don't get me wrong, I'm not claiming Carrara's new tree lab is the second coming of X-Frog, or even Onyx, but I have been able to get more realistic trees than I could using Bryce's tree lab, and one thing I have been known for in Bryce is my trees and vegetation.