In spring of 2015, a massive and synchronous flowering and seeding event of Chusquea montana began in Puyehue National Park, Lake District. We assessed above ground biomass and temporal pattern of productivity and viability of seeds by sampling eight plots and 20 collection boxes, respectively. In addition, we recorded the different phenological stages of the species during this event. The study area was in the sector of Antillanca, dominated by a mixed evergreen-deciduous Nothofagus forest. Biomass values were 33.50 Mg ha^-1 fresh weight and 17.66 Mg ha^-1 dry weight. The peak values of seed production and viability were 146.86 x 10⁶ ± 130.54 x 10⁶ seeds ha^-1 and 87.5 %, respectively. The phenological features observed were similar to those observed for Chusquea quila; nevertheless, mountain climate, where Chusquea montana occurs, was reflected by some differences in maturation and seeding times.