雑草群落の形成過程-第二次遷移の初期段階の解析 I

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  • THE DEVELOPMENTAL PROCESS OF WEED COMMUNITIES EXPERIMENTAL STCDIES ON EARLY STAGES OF A SECONDARY SUCCESSION, I
  • 雑草群落の形成過程-第二次遷移の初期段階の解析-1-
  • ザッソウ グンラク ノ ケイセイ カテイ ダイ2ジ センイ ノ ショキ ダンカイ ノ カイセキ 1

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1. A permanent quadrat of 1 sq. m. was laid in the abandoned farmland in the grounds of the Chiba University where a field experiment concerning the competition between crops and weeds was perfomed. The surface soil was cultivated, mixed, and weeded in January, 1953. There, the developmental process of a weed community was examined. 2. There, at first, appeared a herbaceous community dominated by Ambrosia artemisiaefolia which is often a pioneer plant in the bare area. After the death of the hog weed, the rosettes of Erigeron were found in abundance (Table 1). The hog weed was stratified into the upper and lower layers because of the divergence of the germinating period. It will be a kind of social adaptation (Fig. 1). 3. The combination of dominated life-form and migrule type according to the number of species Is Th-D_4-R_5,which is a usual type of weed communities in the farmland (Table 2). That according to the density is Th-D_1-R_5,which coincides with the first rank of the actual combinations (Table 3). In the growth form spectra (Table 4). the erect form and tufted growth exceed the rosette and prostrate form where the habitat is spatially segregated and especially the rosette plants are to dominate in the following year. 4. Concerning the organizing process of the weed community, the law of geometrical progression can be applied in August when the Ambrosia community of the aestival type arrived at the maximum development (Fig. 2). Such a linear relationship was not recognized before and after August. This is a balance of power relations among species in the form of seasonal aspection or early development. Then it is shown that there is an undulatory process of establishment and breaking in the organisation of a community. 5. The mean area of the commonnest species (M) is related closely with P (dominant ratio)=(number of individuals of the commonnest species)/(total number of individuals) and the gradient of a straight line showing the number of individuals-rank relationship (Table 8,9). The suitability of 2M as a sampling unit should be, in general, determined by the individual structure of a community, which is indicated partly by P and the gradient. The distribution type of the weed community was considered as the POLYA-EGGENEERGER type (Table 10).

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