Silvicultura en Bosques Nativos vol. 1

87 Regeneración y manejo de Nothofagus betuloides SUMMARY Old-growth forests dominated by Nothofagus betuloides in South Patagonia and Tierra del Fuego are uneven-aged. Natural small-scale disturbances are frequent in these forests. Seedlings and saplings of N. betuloides are able to establish, survive, and grow slowly at low light levels (solar radiation transmittances between 3.6 and 17.6 %), persisting suppressed in the shaded understorey for long periods (more than 100 years). Radial growth patterns on juvenile trees growing at the edge of the canopy gaps have shown that they can grow surrounding very small canopy gaps with low radial growth, and then respond to abrupt increases in gap size caused by disturbances to the canopy. Therefore, these results suggest that N. betuloides has greater shade-tolerance. As overstorey trees die and gaps are created in the canopy, understorey trees gradually grow into the canopy, therefore the advanced regeneration may eventually reach the canopy after two or more periods of suppression. Beneath this context, this work has for objective to show the effects of the canopy gaps on some microlcimate variables, regeneration patterns and ground vegetation to promote a new silvicultural practice in uneven-aged N. betuloides forests. The selection method employing a gap-based approach system might be used in order to maintain timber production and the structural richness of these old-growth N. betuloides forests. Key words : Nothofagus betuloides , uneven-aged forest, gap-based silviculture, selection system, advanced regeneration. 5.1 Distribución geográfica Nothofagus betuloides es un árbol endémico de los bosques subantárticos de Chile y Argentina. En Chile es posible encontrarlo desde Valdivia (40º 31’ S) hasta el archipiélago del Cabo de Hornos (55º 31’ S) (Rodríguez y Quezada 2003). En Argentina se puede encontrar entre los 48º S hasta Tierra del Fuego (Dimitri 1972, Veblen et al . 1996). Al norte de su distribución, N. betuloides se desarrolla aproximándose al límite arbóreo, por sobre los 800 y 900 m.s.n.m. en la Cordillera de la Costa y en la Cordillera de losAndes, respectivamente (Donoso yAtienza 1983, Donoso y Donoso 2006). Hacia el sur, N. betuloides conforma los bosques siempreverdes más australes del planeta (Young 1972, Promis et al . 2008), encontrándose desde el nivel del mar y llegando a alcanzar el límite arbóreo en algunos sectores (Young 1972, McQueen 1976, Tuhkanen et al. 1989-1990, Donoso y Donoso 2006). La superficie de bosques chilenos en los que participa N. betuloides alcanza aproximadamente a unos 2.739.906 ha, lo que corresponde al 20,4 % de la superficie nacional de bosques (CONAF et al . 1999). De esta superficie, 1.793.098 ha (65,4 %)