Ecological Studies on Woodlands of Grazing Use : III. Vegetational change of dwarf bamboo type grassland after five months summer grazing

Takiue Pasture of Hida-Osaka Town is located in Gifu Prefecture, in the central part of the main island of Japan. The pasture is divided into four sections, and one of them (the 4th section) being situated at about 1200m above the sea-level and some 50 ha in area, is lately established to be used as a summer grazing pasture for the Japanese black breed of cattle in 1968 (see Fig. 1). Formerly, seedlings of Japanese cypress (Chamaecyparis obtusa) and larch (Larix leptolepis) were planted in this section after the destruction of natural woodland dominated by oak (Quercus mongolica var. grosseserrata) and Japanese cypress with luxuriant understory of dwarf bamboo (Sasa senanensis), but now a pure stand of dwarf bamboos, native plants in this area, so completely covers to hide the tree seedlings. The number of cattle grazed there in 1968 was 76, and the area practically used was less than one third of the section (about 15 ha). On October 22 in the same year, soon after the five months summer grazing, an ecological survey was carried out in this section to investigate the direct effect of summer grazing in the first year upon the vegetation of such a dwarf bamboo type grassland. According to the results of the survey, some matters were clarified as follows : 1) Almost all the vigorous leaves of the dwarf bamboos were lost by cattle grazing, greenish tone of color of the grassland turned to brownish-gray, and the grassland itself seemed to have become quite different in physiognomy. Howerer, few invaders or newly migratory plants were found there, and the scassland scarcely changed in the structure of the community. 2) Not a few tree seedlings were damaged by cattle grazing. Branches were broken by browsing in 15% of Japanese cypress seedlings (1.5-2.0m high), and about 40% of seedlings of larch (1.0-1.5m high) were scratched by trampling at the basal parts of their trunks. 3) The dwarf bamboos in the grazed plots showed a tendency to shorten the height. The higher the culm was, the more it was severely damaged by grazing, and at the end the dwarf bamboos in these plots were more averaged in height with each other than under ungrazed condition (see Fig. 2). 4) Under grazed condition, the dwarf bamboos had many diminutive branches at each node in the upper part of culms over 40cm high above the soil surface, although neither branches near the soil surface nor sprouts from rhizomes were seen. Number of branches per culm were 23.7 in the grazed plots, as against 0.95 in the ungrazed plots (see Tab. 1). 5) The dwarf bamboos in the ungrazed plots had large leaves though comparatively few in number, but the leaves in the grazed plots were very small in shape and abundant. It was ascertained that the average length and the number of leaves in the ungrazed plots were 23.7 cm and 9.2, though 3.6cm and 19.0 respectively in the grazed plots (see Tab. 2). 6) The standing crop (oven dry weight per m^2) of all organs above the ground was measured. It was 1587.3g in the ungrazed plots and 1521.0g in the grazed plots. The dwarf bamboos in the grazed plots were charcteristic in weight that culms (with culm sheaths, branches and leaf sheaths) were heavier and leaves (only leaf blades) were much lighter than those in the ungrazed plots. The weight ratio of leaves to culms was only 1.4% in the former, but was about 30% in the latter (see Tab. 3).