Aiming to the final goal to establish the dendrochronology in tropical trees, three fundamental investigations to get the relationship between growth ring structure and tree growth were carried out.
1. Seasonal characteristics of cambial structure
Eucalyptus camaldulensis etc. grown in seasonal forest in Thailand and Shorea acuminata grown in tropical rain forest in Malaysia were used for the investigation. The observation of seasonal characteristics of cambial structure clarified that cambium showed the structure of cell division even in the mid dry season in Thailand. This is considered to be one of the reasons for the indistinctness of the growth ring boundary.
2. Relationship between elongation growth and radial growths and growth ring formation.
Young trees of Hevea brasiliensis and Acacia mangium were used for the study. Elongation and radial growths were measured every two weeks together with the phenological observation especially of leaves. The growth rings were formed just after the cessation of elongation growth in H.brasiliensis. A.mangium, however, showed not so clear relationship between elongation growth and growth ring.
3. Analysis of growth ring structure in some plantation grown trees.
Some typical plantation trees and plantation grown Dipterocarpaceae trees were used for the experiments. In the disk of each species ring structures which corresponded to growth ring were observed. In some species, however, it was very faint or was not continuous along the circumference. A part of growth ring-like structure joined another ring, In the light microscopy cell structure of growth ring boundary was clarified, that is fiber wall showed thickened structure in most cases. Although some of the growth rings were considered to be so-called "false annual ring", growth ring which corresponded to annual ring was clarified in some species.