Abiotic and vegetation data were collected along two altitudinal transects through mature montane Quereus forests on the Pacific and Atlantic slopes of Costa Rica's Chirrip6 Massif. Between 2000 and 3200 m asl twenty-four 0.05 ha forest plots were selected at altitudinal intervals of 100 m, and eight soil profiles were described at intervals of 200 m. A TWINSPAN classification aided in the determination of eight zonal forest communities on the basis of their floristic composition. They are grouped in two sets of four: (i) the palm-rich lauraceous-fagaceous Lower Montane Mollinedia-Quercus Forests (20(0)-2600 m asl) and (ii) the bamboo-rich myrsinaceous-fagaceous Upper Montane Schefflera-Quercus