I am trying to find out how he did the soft texture on the trees. They mentioned some kind of dry buttercream, but did not go into details. Anyone know how they did it?
I would love to use this in orange for some texture on a large piece of coral for a cake.

yeah they colored buttercreme, than scraped it over a smooth surface and let it harden, than they crushed it into a soft course texture so that it would look like real trees.

He usually uses a meringue buttercream - do you think this is what he did? Would a regular buttercream do this more easily?

This has been discussed here on CC here before, but I couldn't find the original post. If I remember correctly it was suggested by other members that it was crushed dried royal icing.

HTH

I beleive they even said on the show it was royal icing, didn't they?

I think it was buttercream. If it was RI I don't think you'd get that soft, feathery effect. I believe RI would just crack and be hard small pieces. Though it may work, depending on the effect you want, I believe what they used and mentioned was the BC.