Competition, Facilitation, Seed Distribution and the Origin of Patches in a Patagonian Steppe

The Pataxonian steppe is composed mainly of shrubs and tussock grasses organized in two types of patches: scattered grass tussocks in a matrix of bare soil and shrubs, each surrounded by a dense ring of grass tussocks. We analyzed the variation of competition, facilitation, and seed distribution through space and time as major driving forces in the development of this patch structure. Emergence and survival of grass seedlings increased with distance from shrubs when the ring of grasses was left intact. On the contrary, when the ring of grasses was experimentally removed, seedling survival decreased with distance from the shrub. Differences in root density, soil water potential, and evaporation accounted for these patterns (...)