Ecological Studies of Sasa Communities

The characteristics of productive structure and its seasonal changes were analyzed in the closed Sasa kurilensis community at Mt. Waisuhorun, 60km. W from Sapporo, Hokkaido, and in some other Sasa communities. Annual net production was also estimated in those Sasa communities.1. The S. kurilensis community showed a nearly constant standing crop of 11kg. dry weight/m.2 throughout the year. This means that the amount of newly produced part in each organ was almost equal to that of withered part.2. With the foliation of new leaves at the end of June, the 2-year-old leaves generally defoliated to keep the amount of whole leaves at a constant level of ca. 0.85kg. wet weight/m.2, or ca. 5 in leaf area index. Productive structure can rapidly recover after thawing from the inactive state in winter by strong elasticity of culms. These facts must play an important role for the large matter production and the large standing crop of the community.3. Relative light intensities under the Sasa community fall in a narrow range of 1-7%, the mean being 2-3%. Such low light intensities can prevent the invasion of other plant species.4. Dry weight of culms showed nearly a constant value, 7.5kg./m.2, throughout the year. The subterranean parts, however, varied in dry weight, i.e. the maximum of 4.2kg. in early November and minimum of 3.0kg. in mid-August. Culms, branches and rhizomes newly formed during the growing season were 390, 245 and 230g. dry weight/m.2, respectively. A linear relationship was observed between the diameter and the logarithm of dry weight of culms.5. The decrease of dry weight in culms and rhizomes, probably of reserved starch was recognized in late spring-early summer when the rapid growth occurred, and then increased till late autumn. Transformation factor from reserved substances into active organs appeared to be 0.5.6. Sasa kurilensis community kept its daily net production at fairly high level throughout the growing season, and a maximum of newly formed increment was about 11g./m.2/day. The annual net production was estimated to be 1.6kg./m.2/year.7. Productive structure and its seasonal variation were studied also in S. nipponica- and S. nikkoensis-communities. The latter could achieve almost the same amount of net production as that of the S. kurilensis community, in spite of the smaller standing crop.