CAMBIAL ACTIVITY AND RADIAL GROWTH DYNAMICS OF THREE TROPICAL TREE SPECIES AT CHANG ISLAND, THAILAND

Abstract

The cambial activity and radial growth of three tropical species, Tetrameles nudiflora, Hopea pierrei and Cleidion spiciflorum at Chang Island were measured monthly from December 2011 to May 2012 and bi-monthly from June to November 2012. We installed electronic dendrometers to analyse stem diameter variation. Cambial activity was quantified by counting the layers of undifferentiated cells in the cambial zone at 10 randomly chosen positions. The relationships between the cambial activity and climatic factors, i.e. rainfall, temperature, relative humidity and soil moisture were investigated by Pearson’s correlation. The number of cambial layers was significantly correlated with relative humidity. Growth dynamics of the three species differed considerably. The cambium of T. nudiflora appeared active year-long and was most active at the end of August. Cambial activity for H. pierrei and C. spiciflorum was highest at the end of June and July respectively, but was not significantly correlated with climate. Radial growth measurements showed that all three species contracted in the afternoon from 2.30–6.00 p.m., and the maximum enlargement occurred before 9 a.m. In this rainforest with high rainfall trees grow year-round, and radial growth rate depended on the water cycle rather than the weather conditions in the area.