ナミアゲハの個体群動態に関係した先駆樹種・カラスザンショウの肥大成長パターン

抄録

The effect of defoliation by the larvae of a swallowtail butterfly, Papilio xuthus, on the radial and height growth patterns of the host tree, Zanthoxylum ailanthoides, was investigated in a deforested area, Large differences in growth of the tree height were due to suppressions by other plant species at the experimental plots. Each tree was classified into three groups ("tall", "medium"and "short"trees) on the basis of the value of mean relative height (MRH), which was calculated according to its relative height to the surrounding plants. A correlation was observed between the value of MRH in each tree and the radius excluding the bark thickness at the ground level or shoot growth. Higher value of MRH means a "tall" tree which is not covered by other plants. Stem analysis showed that the highest growth rate of annual ring width increment of all trees was achieved within 4 or 5 years after germination. There was a significant time delay in germination between "tall" and "short" trees. Thus, "short" trees, which are suitable hosts of the butterfly larvae, existed in the deforested area only for several years after clear cutting. The females of the swallowtail butterfly concentrated their egg laying on the trees of low MRH. High larval densities did not necessarily cause the low ring width increment of the host tree. The radial and height growth patterns of the host trees are discussed with reference to the ephemerals of habitat suitability for P. xuthus.