Fundamental study for the establishment of dendrochronology in tropical trees

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In tropical trees it is said that growth and/or annual rings are considered to be not so distinct as those of temperate trees. In this research project seasonal characteristics of wood formation were studied to get information related to growth and/or annual rings with special reference to water conditions. Natural and plantation forests were selected in Thailand and Malaysia as the research sites. Results of Thailand are reported in this abstract. Four species, Hopea odorata, Hopea ferrea, Eucalyptus camaldulensis and Tectona grandis were used. For the wood formation study, setting of band-type dendrometer, pinning experiment and collection of wood blocks including cambium were carried out. To investigate water conditions, leaf water potential as well as soil and phloem/xylem moisture contents were measured. The growth ring boundaries were formed in the end of rainy season to early of dry season in 4 species, In detailed observation, however, weak growth ring boundary was formed even in the rainy season if it has low precipitation, Water deficit was considered to affect sensitively cambial activity resulted in the formation of growth ring boundary. In the comparison o」 H. odorata and H. ferrea, leaf water potential of H odorata was higher than that of H. ferrea all through the year. In the former wood formation started following the start of rainy season. In the latter it delayed about 2 months. It was considered because of the delay of the recovery of leaf water potential in the latter due to the severe water stressed condition in the dry season. In the pinning experiment, the extent of wound tissue in the tangential direction was wider than it was estimated. Methodologically it should be reconsidered in the future field investigations.