Fundamental study on the dendrochronology in tropical trees.

为了最终建立热带树木的树干年代学，开展了三项基础性研究，以获得生长轮结构与树木生长的关系。以泰国季节林中生长的赤桉等形成层结构和马来西亚热带雨林中生长的尖叶树为材料，研究了它们的形成层结构的季节特征。通过对形成层结构季节特征的观察，发现泰国旱季中期形成层仍表现出细胞分裂的结构。这被认为是生长环边界模糊的原因之一。巴西橡胶树和马占相思幼树的伸长生长与径向生长和生长轮形成的关系。每两周测量一次伸长和径向生长，同时进行物候观察，特别是叶片的物候观察。这些生长轮是在巴西棘豆伸长生长停止后形成的。而马占相思的伸长生长与生长轮之间的关系不是很明显。对几种人工林树种的年轮结构进行了分析，选取了几种典型的人工林树种和人工林的龙脑香科树种。在每个物种的圆盘中，观察到与生长轮相对应的环结构。然而，在一些物种中，它非常微弱或沿圆周不连续。光镜下可见部分生长环状结构与另一环相连，生长环边界的细胞结构清晰可见，即纤维壁大多呈增厚结构。虽然一些年轮被认为是所谓的“假年轮”，但在一些物种中，与一年轮相对应的生长轮被澄清了。

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 structureEucalyptus 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.