Causes of varying regeneration dynamics of Abies homolepis among topographically distinct stands

Abstract

In order to obtain information on the effects of topography and other environmental variables on the regeneration of Abies homolepis Sieb. et Zucc., one of the main species inhabiting the cool temperate forests of Japan, we examined the population density and size structure of the species in 6 topographically distinct stands in the headwaters of the Kinugawa River in central Japan. The floodplain comprised 3 stands. The stand on the lowest terrace was dominated by the pioneer species, Alnus hirsuta and Toisusu urbaniana, etc. and it had a high density of A. homolepis [diameter at breast height (DBH), ≦10cm]. Although A. homolepis was the most dominant species in the stands on the middle and highest terrace, A. homolepis of DBH 20-60cm was not found in the stand on the highest terrace. This implied a depression of regeneration with progress of succession after flooding. On a steep, rocky slope, the A. homolepis population showed a continuous, inverse J-shaped size distribution, which implied continuous regeneration. In contrast, lower proportions of A. homolepis of small and intermediate sizes were found at two other sites on a mountain slope; this indicated that the species present at these sites showed less continuous regeneration. In addition, inverse correlations were found between sapling density and dwarf bamboo coverage, and sapling density and soil depth, indicating that the sapling density was greater in shallow soil and in places where dwarf bamboo coverage was less. The results of this study implied that flooding or uprooting, which creates disturbances in the soil and result in the generation of bare sites, is favorable for the establishment of A. homolepis. In conclusion, A. homolepis might regenerate vigorously where disturbances in soil are frequent, for example, a steep rocky slope with a thin layer of soil, and behave like an edaphic climax species. On the other hand, this species may behave like a long-lived seral species at sites where disturbances in soil are less frequent, for example, a floodplain or a gentle slope.