The demographic genetic substructuring of local Fagus crenata populations at Ogawa Forest Preserve, Ibaraki Prefecture, central Honshu, Japan, was analyzed by means of demographic parameters and genetic markers using protein polymorphisms (allozymes). All individuals, including seedlings, various sizes of juveniles, and adult trees within two transects were mapped; size‐class structures were analyzed based on DBH and DGH measurements, and their genotypes determined for 11 different allozyme loci (a total of 46 alleles), i.e., Aap1(3 alleles), Adh (3), Amy2 (6), Dia (4), Fum (3), Got1 (5), Got2 (3), Lap (6), Pgi (4), Pgm1 (4), and Pgm2 (5). Critical analyses were conducted to test whether genetic substructuring patterns in these two transects are correlated with the underlying environmental regimes of the habitats. Measurements of relative light intensity, soil moisture, pH, and C‐N content were made for each block in the two transects. Principal component analyses (PCA) of the environmental variables revealed that two components (Z1 and Z2) were closely related to variations in light intensity and soil moisture. The projection diagrams obtained by the environmental variables were then overlaid with the spatially localized patterns of size‐classes and genotype distributions of 11 allozyme loci examined. The results revealed that genetic variations are pooled in the juvenile trees of certain size‐classes, consisting of overlapping generations which occur in the particular sites characterized by environmental regimes. Throughout the regeneration processes, new genetic diversities are introduced through seedlings with new genotypes into the population.

We investigated chronological changes in allozyme diversities in Fagus crenata populations by means of size‐class discriminations, using allozyme variations in two transects established in a mixed beech‐oak forest in the Ogawa Forest Preserve. All individuals within transects were divided into six size‐classes based on their diameters: class 0, seedlings; class 1, juveniles <5 mm; class 2, 5 < juveniles < 10 mm; class 3, 10 < juveniles <25 mm; class 4, 25< juveniles <600 mm; class 5, 600 mm

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Since the end of the glacial age, Picea koyamae has been sparsely distributed in Japan as a relict species and is presently threatened with extinction. We investigated the population structure and genetic structure of nine populations of P. koyamae. Population size was assessed at 9-135 individuals in habitats ranging from 0.5 to 11.5 ha, and seedlings and saplings were observed in all but one particular population, which had a Sasa-type (bamboo grass) forest floor. The effective number of alleles per locus (N e ) within peripheral populations in the Yatsugatake Mountains was 1.8-2.7, much lower than that of core populations in the Akaishi Mountains (2.8-4.3) using five nuclear simple sequence repeat loci. This finding suggests that genetic variation in these populations has been reduced by isolation from other populations. The standardized genetic differentiation among populations (G 0 ST ) was 0.410 and higher than that found in other Japanese conifers, suggesting that isolation and inbreeding have progressed in this species. In two isolated populations at the Yatsugatake Mountains, the fixation index (F IS ) was 0.315-0.354, much higher than the values determined for the other populations (-0.188 to 0.263). This suggests that these two populations have survived several generations while increasing the degree of inbreeding. However, the highest seedling density was in a population with low genetic variation and high F IS . The most serious problems at present appear to be the declining number of mature trees and the deterioration of suitable environments for seedling establishment.