The Japanese Forestry Society Congress Database

We examined occurrence trends of tree species in sugi plantations by comparison with those in natural forests in the warm-temperate region. Of the total 167 species occurred on 348 study plots (181 plantations and 167 natural forests), 96 and 64 species had biased occurrence in natural forests and plantations, respectively. The latter consisted of less numbers of evergreen trees and shrubs, which was thought to be the climax or late-successional species of the region. There were no clear difference in the proportion of seed dispersal types between the two occurrence type. By using a logistic regression analysis, 73 species were given significant models. Of these 73species, 23 species were detected to have a dependence of occurrence on stand age. The species which had dependence on the distance from the natural forests and better light environment were only 10 and 13 species respectively. Eleven species showed their occurrences depending on the time after the latest thinning. These results suggested that most plantations were likely to lack the 'natural forest type' species, and that it would be difficult to improve this lack by thinning practices or extending the rotation of logging.

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To clarify the effect of grazing on understory vegetation in a mid-aged Larix kaempferi plantation, we studied for two years, northern part of Yamanashi prefecture, central Japan. Before grazing, the understory of the study site was mainly dominated by Sasa nipponica, Symplocos chinensis var. leucocarpa, Miscanthus sinensis. After 2-years grazing, while quadratrs dominated by M. sinensis were considerably decreased, those dominated by S. chinensis var. leucocarpa and other shrub species were increased. According to transition matrix using these data, quadratrs dominated by M. sinensis predicted to disappear within 10 years.

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Although many broadleaved tree species are planted as production forest, only few of them grew enough. It seems that the species which is dominant either in edaphic climax or in an early stage of succession is successful to forest.

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In order to analyze forest dynamics, data for the long-term and large-scale observations are necessary. Such data are still in short for ecological studies of conifer plantations. Although plots to investigate standing crops of plantations are abundant in Japan, they are mostly in small area and often lack spatial data of individuals. For example, plots of 20x20 m² may be enough to understand above-ground biomass of young stands. When they become older and larger, however, such plots will give estimation with a large range of error. In this study, we analyze long-term (>60 years) data of old plantations of conifer (>90 years) in the plots with identification of spatial position of each tree. Area of each plot is not so large (40x50 m²). How useful are these plots for the study of structure and dynamics of the plantations? The objective of this study are to analyze 1) growth of standing biomass under the different intensity of thinning and 2) spatial variation of local biomass, and to identify 3) minimum area to estimate mean biomass of old standing crops with reliable accuracy. The data suggested that stands with no history of thinning showed decreasing trend of stand biomass during the last 10 years. Such phenomena could not be found for the 50-years observation, and could be detected for the 60-years data. Continuous observation will show us whether such decline is temporal event or not. The trees showed clumped distribution, rather than uniform pattern. This means that smaller area of investigation possibly overestimate or underestimate of standing biomass of the studied stands.

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