Tree retention is understood as a key practice in creating complexity, leading to heterogeneity in resources and habitats in managed stands. In this article, we clarify the long-term effects of tree retention on stand structure and tree-species composition in a 60-year-old Larix kaempferi plantation in central Japan. In our study plot (1.5 ha) there were 18 stems/ha of retained trees (determined by tree-ring analysis), mostly Quercus crispula. We conducted spatial analyses and tested the hypothesis that tree abundance, size structure, and species composition and diversity change with distance from the retained trees. Near the retained trees, L. kaempferi showed a reduction of 40%-60% in basal area, due presumably to the shading effect. In contrast, the nearby area showed greater species diversity in the canopy layer. The retained trees created patches of different species composition in the understory. The spatial gradient of shade and colonization opportunity provided by retained trees greatly affect the distribution of the colonized species, according to their shade tolerance and seeddispersal ability, which resulted in the stand structure with a heterogeneous shrub-layer vegetation. Retention proved particularly important for the enhancement and long-term maintenance of structural and compositional complexity in L. kaempferi plantations.
Examination of Appropriate Seed Transfer Zones Based on Genetic Differentiation among Natural Populations of Alnus hirsuta and Stable Production of Its Local Planting Stocks, in Toyama Prefecture, Japan. J. Jpn. For. Soc. 91: 173 177. To examine appropriate seed transfer zones based on genetic differentiation of Alnus hirsuta, we investigated chloroplast DNA haplotypes at 13 natural forest sites, 5 commercial slope afforestation sites, and 4 commercial forest protection sites in Toyama Prefecture, Japan. The haplotypes of Alnus hirsuta in the natural forest were classified into two types: those in high-altitude areas at 1,100 m or higher Type I , and those in areas below this altitude Type II. The haplotypes of trees used in slope afforestation and forest protection were all Type II, regardless of altitude. Because Alnus hirsuta is wind pollinated and sets flowers several years after planting, there is a high risk of genetic disturbance by hybridization in high-altitude areas where seedlings of different halpotypes are planted. In afforestation industries, therefore, it will be necessary to take account of the haplotypes. With the aim of achieving stable production of Alnus hirsuta in local planting stocks, we examined the seed yield at high altitude in the natural forest. Our results showed that year-to-year variations were extremely large, making it difficult to harvest a stable level of seeds every year. However, because the seeds are highly preservable, it should be possible to cope with this problem by setting up seed-production stands based on analysis of the chloroplast DNA, and then harvesting a large amount of seeds in high-yield years and storing them until the next high-yield year, in order to ensure stable production of Alnus hirsuta in local planting stocks.
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