I haven't seen any tutorials yet on how to go about constructing scenes of such detail in Carrara, but having this actual scene file would be most instructive in itself. I would be able to analyze the scene size he starts with (small, medium, large), lighting, terrain base shaders and textures, plant editor settings for those amazing trees, replicator settings and maps, lighting set-up, etc.

Patrick has very kindly made his default tree shaders with translucency available at digitalpainters,net as well as a very nice tut on building your own plants in Carrara using an actual photograph at polyloop.net. HowieFarkes has some great ferns and other plants he generously made available as a freebie D/L at digitalpainters.net. These may not be the tutorial for the grand scene we are hoping for, but they do provide some of the building blocks.