In temperate rainforests at mid-elevation (> 600 m a.s.l.) in South-America the Chusquea culeou bamboo (colihue) is the dominant understory species and potentially can impede tree regeneration. Dieback of colihue subsequent to its gregarious flowering may result in an opportunity for tree establishment or growth release of previously suppressed juvenile trees, especially in canopy gaps. In this research we evaluated the bamboo dieback effect on tree species establishment and advance regeneration growth in two old-growth forests. The first forest is dominated by Nothofagus dombeyi-Saxegothaea-conspicua-Dasyphyllum diacantoides and the second is dominated by Araucaria araucana-Nothofagus, located in the Andean Cordillera of south-central Chile. In each forest (San Pablo de Tregua and Quetrupillán) following the gregarious flowering and dieback of colihue, between 2001 and 2003, we recorded new establishment of colihue and tree demographic changes and growth of advance regeneration in gaps with live versus dead colihue. In both forests the mortality of the advance regeneration was higher in gaps with dead colihue. Only in San Pablo was the height growth of Saxegothaea conspicua higher in gaps with dead colihue. New tree establishment did not show differences between flowered and non-flowered conditions. The recruitment of colihue seedlings was higher in gaps with dead colihue in both forests, being the clearest pattern of response to this dieback event. Overall, similar to other studies, the colihue dieback results in growth of advance regeneration, but it did not represent a major opportunity for new tree establishment in these forests.