The nitrogen uptake and turnover were investigated with isotopic estimation method by using pot-cultured 2-year-old Konara (Quercus serrata) seedlings. To make a distinction between the nitrogen derived from soil as fertility in current year and the nitrogen accumulated in the seedling before the beginning of culture, potassium nitrate-¹⁵N were applied as labeled nitrogen for12months. The amount of nitrogen derived from soil as fertility in current year was64.68mg·tree^-1with the average of five seedlings and about74%of it was accumulated in belowground part of tree. In belowground part of tree, the ratio of nitrogen derived from soil in current year to total nitrogen was higher in fine root. This result suggests that the structural formation of fine root depends on the nitrogen absorbed from soil in current year. The ratio of nitrogen derived from soil in current year to total nitrogen was relatively lower in leaf litter than in aboveground part of tree. But the amount of total nitrogen in leaf litter depended on the amount of nitrogen derived from soil and accumulated in aboveground part of trees.The concentration of nitrogen derived from soil in current year was higher in sprout shoots that tooke a place of dead of top shoot.

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In order to explore the effects of pine wilt disease on the stand structure of Pinus denszflora forests in urban fringe areas of Okayama City, we researched two damaged forest stands and one undamaged forest stand. In one of the damaged stands, selective felling of dead pine trees were conducted, and in the other damaged stand, no operations to protect pine treees were conducted. Stand structures varied in the studied stands. Biomass in the two damaged stands were reduced by pine wilt disese damage. In the damaged stand where the selective felling operation was conducted, biomass of the understorey was remarkably reduced. In both the undamaged stand and the damaged stand without protection, evergreen broad-leaved species were abundant in small size classes and were predominate in the understorey. In the damaged stand with the selective felling operation, deciduous broad-leaved species were abundant in small size classes and were predominate in the understorey. It was thought that the selective felling operation disturbed the understorey of the stand and this disturbance caused the establishment of shade intolerant species. From the analysis of diameter increments, it was presumed that the grawth of remnant trees had been accelerated after the outbreak of the disease. It was assumed that the remnant trees had been released from the suppression because the canopy trees of P.densiflora were dead and thus decreased by pine wilt disease. From our research we concluded that pine wilt disease accelerated the succession of the pine forests.However, selective felling operations disturbed the forest stand and decelerated the succession.

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