Growth and development responses of three Acacia species to long-term light regimes.

Abstract

Three species of Acacia which are used in various forestry systems in Micronesia are Acacia confusa, A. mangium and A. auriculiformis. The responses of these species to limited light have not been established. The objective of this study was to determine the growth responses of seedlings of the 3 species to light ranging from 19, 44 and 100% of full sunlight (in a shade house) in order to determine the relative tolerance of the species to shade. Over the course of the 3-month experiment several common adaptations to low light occurred in all the species, such as increased leaf surface area in relation to mass of supportive tissue and reduced leaf mass per unit leaf area. However, other adaptations to low light were not evident. Numerous indicators of growth were reduced at low levels of sunlight transmission. The relative reduction in growth at 19 and 100% transmission was similar for each species. The results indicate that these Acacia species exhibit some adaptations to development in limited light, but they are not tolerant of shade. All 3 species are thus classified as shade avoiders, and have limited application under shaded conditions in any Pacific island forestry system.