Sand dunes develop over time and go through a range of stages from mobile shifting sands near the sea, to fixed dunes further inland. Over time, organic matter accumulates in the soil, which increases the amount of nutrients available to plants. This means that a larger number of different species can survive, and the dune becomes more species diverse.
Oxytropis halleri is another member of the pea family, which can survive in the relatively nutrient poor dune soils by fixing atmospheric Nitrogen in its root nodules.