I can imagine this mimics plant growth on natural slopes. Debris, like fallen branches, would catch the litter, stopping it falling further down the slope, creating a little build up and oasis where a seed would have enough time to sprout and establish itself. Once established that plant would be a barricade in itself and help others become established.
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Yup! That is the basic idea and in the areas where my plants are thick enough I don't have to worry about creating these structures. But it helps a lot to get things established :)