山陽中部シイ群落の発達段階について

抄録

1. The Shiia community of the central part of Sanyo district was investigated in 22 stands to observe the developmental stages of the community and the resultant changes in its composition and structure. 2. The ratio (in percentage) of the number of large diameter trees of Shiia spp. to the total of the same species was taken as an indicator of the developmental degree of the Shiia community. All the stands, excepting two on N-slope, were arranged in a gradual increasing order of the ratio, and these were divided into five groups by uniform interval (viz. interval is 20%). The series of stand groups thus obtained seems to show a developmental series of the Shiia community (Table 1). 3. In the series of the stand groups mentioned above, Shiia spp. shows the following trends : (a) gradual increase-maximum-gradual decrease in relative dominances and in total basal area, (b) gradual increase in mean area and average d.b.h., and (c) gradual decrease in density (Table 2 and Fig.2). These trends are nearly in agreement with the theoretical changes of these characters observed in the developmental series of the communities. 4. As for the relations between the developmental stages and the dominant species of the forest floor, it is found that Dicranopteris glauca or Bladhia japonica is a dominant species in undeveloped stands, while Dryopteris erythrosora is dominant in developed stands (Fig.3). Hence the Dryopteris erythrosora-floor type is taken as an indicator of the developed Shiia community in this region. 5. As regards the life-form spectra of Shiia community, the phanerophytes show, on the whole, the greatest percentage, and the hemicryptophytes, chamaephytes and epiphytes show lower percentages while the geophytes and therophytes are not found in any stand. Along the developmental progress from undeveloped to developed stands, the changes in spectra are relatively small, but in the case of hemicryptophytes, a gradual increase is observed (Table 3).