1996 Volume 13 Issue 2 Pages 59-72
Altitudinal distributions of vegetation were studied on Mt. Hachijo-Fuji (854m ; a Holocene volcano) and Mt. Mihara (701m ; a Pleistocene volcano) in Hachijo-jima Island, part of the Izu Islands group, and were compared with those on Mt. Kaimon-dake (922m ; a Holocene volcano) and Kuro-shima Island (622m ; a Pleistocene volcano) situated in southern Kyushu. Kaimon-dake and Kuro-shima have similar climatic and geological conditions to Hachijo-jima. In Hachijo-jima, a Persea thunbergii zone (below 650m) and Eurya japonica zone (above 650m) on Hachijo-Fuji, and a Castanopsis cuspidata var. sieboldii zone (below 600m) and P. thunbergii zone (600-700m) on Mihara were recognized. In southern Kyushu, a Quercus glauca zone (below 300m), P. thunbergii zone (300-500m) , Quercus acuta zone (500-650m) and E. japonica zone (above 650m) on Kaimon-dake, and a C. cuspidata zone (below 550m) and Q. acuta zone (above 550m) on Kuro-shima were recognized. The dominance of P. thunbergii on the Holocene volcanos (Hachijo-Fuji and Kaimon-dake) and of C. cuspidata on the Pleistocene volcanos (Mihara and Kuro-shima) seems to arise from succession from P. thunbergii forest to C. cuspidata forest. On the other hand C. cuspidata, P. thunbergii and E. japonica had wider dominant areas in Hachijo-jima along altitudinal gradients than on Kaimon-dake and Kuro-shima. This fact suggests niche expansions of these species in Hachijo-jima, due to the lack of evergreen Quercus species. In life form, evergreen nothophyll trees were dominant up to the top of the mountains of Mihara and Kuro-shima, below 600m on Hachijo-Fuji and below 650m on Kaimon-dake. Evergreen microphyll trees were dominant above the areas where evergreen nothophyll trees were dominant on the latter two Holocene volcanos. The altitudinal distributions of life forms were similar between the two Holocene volcanos, and between the two Pleistocene volcanos.
