放牧地における植生の連続性および撹乱に対する指標植物

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1. Nineteen vegetation stands of a grazing grassland, located at Sayoto in the Chugoku Mountains were investigated as to the distributional pattern of plant populations and the indicator plants for disturbance. Each stand was sampled with 250 quadrats of (20×20cm), and the quantitative relations of the plant populations were expressed as frequency percentages. 2. The distributional interchange of four principal species was tested by the method of the leading dominant, and the adaptation number for these species was decided (Table 1). To express the numerical distance between the treated stands, frequency index of each stand was calculated by the following formula : Frequency index =((a×1)+(b×2)+(c×3)+(d×4))/(a+b+c+d)×100 in which a, b, c, and d are the frequency percentage of Miscanthus sinensis, Arundinella hirta, Zoysia japonica, and Plantago asiatica, respectively. The resulting index has a range from 100 to 400,and in this study from 133 to 390. The treated stands were arranged along the numerical order of the index (Table 2). 3. The frequency percentage of each species in each stand was plotted in the above mentioned order of stands. The distributional curve of each species was drawn through these points (Fig. 1). From the resulting curves, it is recognized that the distributional curve is generally of a binomial or bell-shaped form or a portion of it, that the plant species differ from each other in either the optimum range of development or the tolerance, or in both, and that the investigated grassland vegetation represents a continuum in which the principal species distribute continuously from the one end dominated by Miscanthus sinensis, through the intermediate stands dominated respectively by Arundinella hirta and Zoysia japonica, to the other end dominated by Plantago asiatica. It may be convenient for communicative purpose that, dividing the vegetational continuum, the community-type is designated with a single dominant species in this study, for the vegetation type in which Miscanthus sinensis is dominant, although the community-types are neither homogeneous within a particular type nor discrete between them. 4. Occurrence frequencies of dungs and trails of livestock, which indicate indirectly the degree of disturbance caused by treading, were examined in the treated stands. It is found that both frequency percentages increase from the stands of low frequency indices to those of high ones (Table 3). This fact shows that the vegetational continuum of the grazing grassland is pararell with the gradient of the disturbance pressure, from light to heavy conditions, and that, therefore, the plant populations can be used as an indicator for the disturbance condition. 5. Component species of the investigated vegetation were grouped into five groups in terms of the optimum range of development as (Fig. 2) : 1). species group, the optimum range of development of which is in Miscanthus community (Frequency index 100〜150), and which indicates the light conditions of disturbance and includes shrubs, tall grasses, and tall forbs; 2) species group, the optimum range of which in Arundinella community (F. I. 150〜250), and which indicates the medium conditions ; 3) species group, the optimum range of which in Zoysia community (F.I. 250〜350), and which indicates the medium conditions; 3) species group, the optimum range of which in Plantago community (F.I. 350〜400), and which indicates the heaviest conditions of disturbance and includes annual plants and ruderal weeds seen in the grassland; 5) accidental species group which has no indicator value.
日本生態学会の論文
1958-10-30

放牧地における植生の連続性および撹乱に対する指標植物

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