Sex Expressions and Size Structures of a Dioecious Canopy Tree Species, Fraxinus mandshurica var. japonica

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Fraxinus mandshurica var. japonica is a dioecious canopy tree species that widely distributes in riparian forests in Hokkaido. We investigated sex expressions and size structures in DBHs of F. mandshurica var. japonica in the Tokyo University Forest in Hokkaido (Furano). In the Iwanazawa large study area (18.75 ha) located in natural riparian forests, the numbers of juvenile, female and male trees were 135 (19.6%), 293 (42.6%), and 260 (37.8%), respectively. The sex ratio of flowered trees did not significantly differ from 1 : 1. Juvenile trees were significantly smaller than flowered trees. Size structures were not significantly different between female and male trees. We also investigated those of F. mandshurica var. japonica in 27-yr and 50-yr artificial forests. Only 4 out of 525 trees (0.8%) flowered in the 27-yr forest. In contrast, 272 out of 558 trees (48.7%) flowered in the 50-yr forest. In the 50-yr forest, size structures of both juvenile versus flowered trees and female versus male trees were similar to those in the natural riparian forest. In addition, we found that sex expressions of 98 phenotypically superior trees of F. mandshurica var. japonica were significantly male-biased. As F. mandshurica var. japonica is important commercial species that is superior in wood quality and straightness, managements of those sex expressions in forestry should be considered.
日本森林学会の論文