The geometry of the canopy of a dipterocarp rain forest in Sumatra

A study was conducted in a lowland dipterocarp rain forest in Sumatra to assess the structure and dynamics of the forest canopy. The canopy structure was analysed at different scales, including a previous mapping of a 5 ha forest mosaic and an interpretation of the canopy architecture, along a horizontal gradient between the high forest and a 320 m2 treefall. Canopy geometry was ascertained by analysis of digitized zenithal hemispherical photographs sampled at 25 near-ground sites. Gap size, morphology and dispersion varied continuously from the high forest to the treefall. An asymmetric pattern of gaps about the zenith was characteristic of almost all forest sites. The spatial dispersion of gaps was random in the high forest. It tended to be dumped in the forest border and in the treefall. Plant area indices ranged from 6.5 in the high forest to 2.9 in the treefall. These values reflect a reduced leaf area during a severe dry spell, at the time of measurements. Inclination angles of canopy elements were highly correlated with gap dispersion and canopy openness, as observed from the high forest to the treefall. Implications of canopy heterogeneity on the distribution of light were analysed. The importance of lateral light penetrating from the forest border into the high forest is stressed. The canopy gradient of architecture and geometry from the high forest to the treefall and the very diverse structure of the high forest are emphasized.