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

Abstract

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.

Nothofagus Betuloides (Mirb.) Oerst 1871 (Fagales: Nothofagaceae) Forests in Southern Patagonia and Tierra Del Fuego

“…In the mixed N. betuloides -N. pumilio forest, however, the uprooting of trees was by far the most frequent cause of tree mortality, accounting for 70 % of the tree-falls, compared to only 24 % snapped trees. This largely corresponded with the findings from Tierra del Fuego (Rebertus & Veblen 1993a).…”

“…As N. betuloides has a relatively low light compensation point for net positive photosynthesis, seedlings can establish under closed canopy conditions. N. betuloides can form an abundant stock of persistent seedlings or saplings, surviving in the understorey for many decades and even exceeding one hundred years (Rebertus & Veblen 1993a;Veblen et al 1996) at high elevations or latitudes, where there is little competition from ground flora.…”

“…In pure N. betuloides stands, canopy openings can occur as interwoven gap complexes where discrete gaps are not apparent (Rebertus & Veblen 1993a (Promis et al submitted). In Tierra del Fuego a patch mosaic pattern has been observed in Nothofagus forests, with patches of younger trees neighbouring larger patches of old forest, forming multicohort stands (Gutiérrez et al 1991).…”

“…In most cases, windthrow of individual trees creates canopy gaps smaller than 200 m 2 (Rebertus & Veblen 1993a;Gutiérrez 1994). In pure N. betuloides stands, canopy openings can occur as interwoven gap complexes where discrete gaps are not apparent (Rebertus & Veblen 1993a (Promis et al submitted).…”

Tree-fall gaps and patterns of tree recruitment and growth in Andean old-growth forests in south-central Chile

“…All species (the emergent N. dombeyi, and dominant canopy species L. philippiana, S. conspicua, and D. diacanthoides) participated with similar proportions as gap-makers; however, N. dombeyi and S. conspicua accounted for the high total area in expanded gaps (42 % and 41 %) in each forest. As in other temperate forests in the southern hemisphere (Veblen 1985a, Steward et al 1991, Rebertus and Veblen 1993, Gutiérrez et al 2009), most gaps in NF and STF were originated by wind-snaps followed by upturned root-plates. Similarly, gap size was importantly determined by forest structure and composition.…”