Bamboos of the genus Chusquea are aggressive colonisers of tree-fall gaps in the temperate rain forests of southern Chile. Chusquea thickets inhibit regeneration of tree species, suggesting that light levels beneath bamboo-filled gaps may be lower than beneath tall forest. Two LAI-2000 canopy analysers were used to compare diffuse light availability beneath five Chusquea quila thickets and five neighbouring tall forest stands, in a low altitude (<FONT FACE=Symbol>È</FONT> 400 m a.s.l.) old-growth temperate rain forest in Parque Nacional Puyehue (40º39'S). Leaf area indices (LAI) of these two vegetation phases are also compared. Average diffuse light levels beneath bamboo thickets (1.5 %) were only slightly lower than those beneath tall forest (1.7 %). Similarly, mean leaf area index of Chusquea thickets (6.1) was slightly higher than that calculated for tall forest stands (5.3). However, measurement of leaf area index with the LAI-2000 is likely to overestimate the actual photosynthetic surface area of bamboo thickets, due to retention of dead leaves by Chusquea. On the other hand, LAI of tall forest stands is underestimated, due to the omission of forest floor vegetation < 50 cm tall. The abundance of Chusquea thickets in old-growth forest, and their ability to retain sites by suppression of tree regeneration, suggests that a two-phase positive-feedback vegetation switch model is appropriate for the dynamics of these forests