Such an interesting thread. I must reply and hope it is of some help.

You can use the particle generator--also see the browser---for the snow..  If you have actual images of snow crystals they can be the objects for the particles for the close ups. ( My imagination boggles at the beautiful effects you could attain)

For the second question, you could create your own "stump" in the Carrara vertex modeller to "match" the tree. (locate it accurately over the tree) then --?-- can you take the tree into the vertex modeller and delete the polygons at the bottom as requred???

Then, because you have two objects, you can do your "falling" to just the one, leaving the other.

Now I just have to try my wild first thoughts out for myself.

And Mark replied first with a similar answer which makes this old bloke verry happy!

bwtr