Tree Light Cache

I recently upgraded my machine at home from 6gb to 18gb or ram (among other things) so I decided to experiment a little with some stuff that I typically used sparingly. After a few hours I'd made a scene that I thought played with displacement, caustics, volumetric fog and environment simulation in a pretty tasteful way. Then, I hit render and went to sleep expecting not to run out of RAM (as my test renders had consumed at most 8gb) and was a little surprised to find the renderer 'unloading geometry' when I woke, estimating another 24 hours. That's now risen to 33+ but fortunately I have enough spare ram to run another instance and I think the above image actually looks quite nice so here it is.