Temporal Change in Vertical Distribution of Woody Vegetation on the Flank of Sakurajima Volcano, Southern Kyushu, Japan

This study explained vertical distributions and growth environments for woody vegetation. It had been degenerated by long-term volcanic activity of Sakurajima; vegetation and thicknesses of tephra layers and forest soils were investigated at 5 sites (250-700 m in altitude) with different altitudes localized at the northwestern-northern flanks of Sakurajima in Kagoshima Prefecture. The results in 2015 were compared with the vertical distribution of woody vegetation in 1963, when the volcanic activity of Sakurajima was relatively moderate. Thus, we investigated temporal changes in the vertical distribution of woody vegetation owing to volcanic activity over about 50 years (1963-2015). We indicated altitude decreased, the number of woody vegetation, number of species, sum of cross-sectional area of tree diameter at breast height, Fisher-Williams's diversity index ${\alpha}$, and forest soil thickness increased. However, these values were found to be degenerated when compared to climax forest values, and succession was incomplete. It seems that because the woody vegetation of the flank was affected by volcanic activity for a long time, exposing them to severe growth environments, areas with lower altitudes became distant from the craters of Sakurajima, thereby weakening the effect of volcanic activity in these areas at lower altitudes. a at the same altitudes over about 50 years (1963-2015) decreased by about 31-72%, and the sum of the cross-sectional area in tree diameter at breast heights decreased by about 14-62%. Thus, comparative growth environments for woody vegetation in 2015 were more severe than that of 1963, with respect to tephra layer thickness. In addition, for vegetation succession in the flank of Sakurajima, vegetation restoration should be promoted through the introduction of artificial woody plants covered by symbiotic microorganisms or organic materials.