Structure and tree‐fall gap dynamics of old‐growth Nothofagus forests in Tierra del Fuego, Argentina

Abstract

Tree size and age structure, tree‐fall and gap characteristics, and regeneration in gaps were studied in Nothofagus‐dominated old‐growth forests in Tierra del Fuego, Argentina. Gap‐phase regeneration has resulted in all‐aged populations for N. pumilio, N. betuloides, and Drimys winteri, and regeneration in gaps appears to be maintaining coexistence between species in mixed stands. N. betuloides fills many gaps via advance regeneration and some individuals persist for > 150 yr in the understory. Multiple periods of release and suppression indicate that N. betuloides may take advantage of several gap events to reach the main canopy. Likewise, Drimys grows well under closed canopy and can rapidly respond to gap formation, sometimes impeding the regeneration of N. betuloides. In contrast, N. pumilio regenerates in gaps mainly from seed or from advance regeneration of small, ephemeral seedlings. Gap turnover times in Fuegian forests were estimated at 300 ‐ 500 yr, although gap formation was highly episodic and possibly associated with regionally extensive windstorms, earthquakes, and stand‐level dieback. 92 % of gaps involved multiple tree‐falls, and at least 53 % involved secondary expansion. Gap and tree‐fall characteristics in Tierra del Fuego were similar to results from northern Patagonia, Chile, and New Zealand; however, we emphasize that regeneration of Nothofagus spp. and Drimys winteri in gaps depends on associated vegetation and varies along both local and regional environmental gradients.