In the rain shadow of the Andes in northern Patagonia, the evergreen beech Nothofagusdombeyi occurs in mixed stands with the xeric trees Austrocedruschilensis and (or) Nothofagusantarctica. In two old-growth stands (>150 years old), size and age structures, treefall patterns, and regeneration responses to treefalls were examined. In the stand codominated by N. dombeyi and Austrocedrus, recruitment of both species occurs in small treefall gaps. The relative proportions of treefalls and potential successors in gaps imply that gap-phase regeneration is maintaining this stand in compositional equilibrium. In the second stand, N. antarctica was formerly a common canopy tree, but currently is not regenerating in treefall gaps; gaps are occupied instead by N. dombeyi. The successful regeneration of N. dombeyi in small treefall gaps in Patagonian forests contrasts with the dependence of this species on large-scale exogenous disturbance for its regeneration in lowland and montane Chilean rain forests. Small-scale gap-phase regeneration of N. dombeyi in Patagonian forests is successful because of (i) the lack of competing shade-tolerant tree species and (ii) the inability of understory bamboos to form dence understories in these relatively xeric habitats.
