RADIATION USE EFFICIENCY AND ABOVE - GROUND BIOMASS PRODUCTION OF SELECTED FOREST TREE SPECIES

W A J M De Costa and K G D Jayaweera
University of Peradeniya

Radiation use efficiency (RUE), defined as biomass produced per unit of radiation intercepted, is considered a genotype-specific constant. If the amount of radiation intercepted is known, RUE can be used to predict the potential biomass production of a given tree species. A comparative growth analysis was done on some selected species, with the objective of determining their light interception characteristics, biomass production, and RUE.

Similar-aged seedlings of six forest tree species: Acacia mangium, Eucalyptus grandis, Leucaena leucocephala, Swietenia macrophylla, Azadirachta indica, and Tectona grandis, were planted at the university farm, Peradeniya, from July 1995 to June 1996. Regular sampling was done to determine above-ground biomass and leaf area. Canopy radiation interception was estimated from simultaneous measurements of incident and transmitted radiation, by tube solarimeters.

In all six species, above-ground biomass production was found to be linearly related to cumulative intercepted radiation. The slopes of the relationships, which indicate RUE, showed significant inter-species variation. The greatest RUE was observed in E. grandis (3.05 gMJ-1) and the least in Azadarachta indica (0.296 gMJ-1). The differences in RUE were primarily responsible for the differences between species in above-ground biomass production. Radiation interception by the canopies of the different species was characterized by the light extinction coefficient, which showed significant inter-species variation. These parameters offer a promising approach for modelling and prediction of biomass production by forest tree species.

Department of Forestry and Environmental Science,
University of Sri Jayewardenepura,Sri Lanka. 1999. All rights reserved.