TAKAYANAGI Emiko, KAMIJO Takashi, OGAWA Mihuyu and TSUYAMA Ikutaro University of Tsukuba, and Japan Science and Technology Corporation, Japan Gap regeneration in mixed deciduous broadleaf / conifer forest on Okukinu, Central Honshu, Japan The gap regeneration process and gap characteristics in mixed deciduous broadleaf / conifer forest were investigated in Okukinu. The area of this study is located in Tochigi prefecture, Central Honshu of Japan (36 52' N, 139 25' E, 1550 m a.s.l). The following four regeneration categories were defined and used in this study: canopy tree, gap maker, suppressed sapling, and gap sapling. Species name and d.b.h. of canopy tree and suppressed sapling were recorded along transect lines using the point-centered quarter method. The percentage of the Wisconsin importance value (PWIV) was used to describe the dominance of canopy tree and suppressed sapling. All gaps whose center were within 10 m either side of the transect lines was described, and we found 12 gap within 1.64 ha. Species name and d.b.h. of all gap makers, and gap sapling in each gap were recorded. We also recorded gap area and the reason of gapmaker dying (i.e. standing dead, trunk broken, and uproot).    Percentage of gap areas to surveyed area, gap density and mean gap size were 7.6 %, 7.3 ha - 1 104.5 m2. 91.7 % of gaps were due to the death of multiple gapmakers. Canopy trees more often died trunk broken (72.1 %).    In canopy, Abies homolepis was the dominant species with the highest PWIV. The second and third dominant species in canopy were Tsuga diversifolia and Prunus ssiori. The maximum d.b.h. of Abies homolepis, Tsuga diversifolia, and Prunus ssiori were 133.0 cm, 72.2 cm, and 54.4 cm, respectively. Abies homolepis showed a discontinuous size structure. In suppressed and gap saplings, the frequency of Acer japoincum, Prunus ssiori, and Tsuga diversifolia were high, while those of Abies homolepis were extremely low. Abies homolepis became gapmaker more frequently (53%) than other species.    Prunus ssiori, Tsuga diversifolia occurred in both suppressed and gap saplings, implying that they regenerate in gaps from advance regenerations recruited before gap formation. In contrast to Prunus ssiori and Tsuga diversifolia, Abies homolepis did not regenerate in gap. Abies homolepis can regenerate after the large disturbance such as catastrophic storms causing serious windfall. BACK TO THE PROGRAM