Ecological Characteristics and Dry Matter Production of Some Native Grasses in Japan : I. Annual growth pattern of Sasa nipponica community

For a step to decide the suitable grazing periods which enable to utilize in the succeeding years and to know the cutting time for effective destruction of Sasa nipponica community, an attempt was made on investigating the annual growth pattern of its community, viz., seasonal fluctuation of dry weight of each plant organ, number of culm, leaf area, productive structure, and number of winter-bud. This experiment was conducted in a closed plant community extenaing on southern slope of Mt. Asama, Nagano prefecture. 1. The biomass above ground increased rapidly from spring to summer, reached maximum in late August, and turned to decrease gradually towards spring in the next year. Contrastingly, the biomass under ground showed a trend of decrease from mid-spring to summer and of increase towards late autumn. Thus, total biomass has kept almost constant throughout the year (Table 1), suggesting that the amount of newly produced plant organs is almost equal to the withered organs in this closed community. 2. Leaf area index (LAI) in the community varied in similar way with the biomass above ground and closely related to the fluctuation of the number of leaves emerged on current culms (Tables 1 and 3). 3. Height and biomass of the wintered plant were exceeded by those of the currently sprouted in June and almost withered at the lower layer of the community untill December. Therefore, it was suggested that average life span of aboveground part in the closed community of Sasa nipponica was about 18-20 months after new shoot sprouted on the ground surface (Tables 1 and 2). Ratio of the aboveground parts to underground parts (T/R ratio) showed muximum value in summer and minimum one in winter (Table 1). 5. Productive structure of the community varied with the season (Fig.1), coinciding with the seasonal pattern of dry weight fluctuation of each organ as indicated in Table 1. Relative light intensities on the ground surface in the community ranged from 10 to 20 percent during the period of winter to spring and 1-5 percent during the growing season. The extinction coefficient of light in the community showed narrow range 0.742-0.778. 6. Number of winter-buds on rhizome also showed a seasonal variation: most of them sprouted during the end of April to the end of May ; they extremly decreased in summer and turned to increase rapidly during September to October and maintained the fixed value hereafter (Fig.2). Contrastingly, number of new rhizome increased rapidly during June to August. 7. With the results above, it was suggested that the suitable grazing periods for the utilization in the succeeding years was late autumn to spring and the cutting time for the effective destruction of Sasa nipponica community was summer.