Donald Schnell states in his book that nonsphagnous mosses are actually detrimental to collections... in addition to crowding out small plants, he says there is evidence that they secrete toxins that retard seed plant growth.
I happen to like a layer of nonsphagnous moss on the soil surface with larger sundews and Sarracenia, especially for outdoor pots; it holds the soil in place when it rains. I am also using U. livida for much the same reason now, though.
What is the collective wisdom on such moss, yay or nay? Has anybody run an experiment with two otherwise-identical collections to determine and retardant effect the moss has on established plants?