Genetic studies in natural populations of forest trees : III. Genetic differentiation within a forest of Cryptomeria japonica.

The present study deals with the genetic differentiation within a natural forest of Cryptomeria japonica. Needle leaves were collected from approximately 50 trees in each of three sites, called subpopulations I, II and III, located at the apices of a triangle. The distances from each other among these three subpopulations were 760 m or 1,300 m. It was found, by an electrophoretic study of peroxidase, that the mean number of isozyme bands exhibited per individual tree was 11.68 in I, 13.73 in II and 12.53 in III. The t-test revealed that the differences between I and II and between II and III were statistically significant. The frequency of occurrence of each band was compared among the subpopulations. It was found that the variation among the three subpopulations was statistically significant. Not a few papers dealing with the study of pollen dispersal in coniferous trees have been published so far. Some of the authors consider that the distance of pollen dispersal is short and gene flow among subpopulations within a forest seldom occurs, while others are of the opinion that pollen travels long distances and no effective isolation is possible within a forest. Findings from the present study support the former view. They show that subpopulations within a forest of Cryptomeria japonica are genetically differentiated from each other, i. e. Sewall Wright's neighbourhood size is small in Cryptomeria japonica.