I would like to know how to mask certain parts of a terrain. Say, for example, that I want to create a scene with both sand dunes, and mountains, being mixed together, like in the attachment. How would I do that? I am not yet a fullblown T2 user, so please make the explanations as simple as possible.
Possibly the simplest solution (others may disagree :) ) would be to plug your dune shader into one input of a "merge shader" and your mountains into the other and select by (Raise by highest). There are of course other solutions.
This looks good to me. If you would like a different ecosystem on the slopes, I would add a new Surface Layer. This new layer would use altitude constraints so it could be confined to the slopes. (slope constraints may do the trick also)