EXPERIMENTAL STUDIES ON EARLY STAGES OF SECONDARY SUCCESSION III

Abstract

1)Experiments for analysing the developmental process of plant communities on 1-meter permanent quadrates from 1954 to 1957 are reported. The experimental treatments of the quadrates at the beginning are by exchanging the soi (to exchange the surface soil for the subsoil)and by burning the soil (to burn the surface soil 5cm deep). 2) Burned-soil plot : -The floristic composition (Table 1)shows a yearly change of the dominants : Setaria-Digitaria-Bromus, which differs from that of early stages of a normal successional change in this place : Ambrosia-Erigeron (-Imperata-Miscanthus). The dominance-rank relations (Fig. 1) and composition curve (Fig. 2) show the differentiation of species groups and their development. The biological spectra (Tables2,3) indicate a degree of progression in the succession according to the increase of H, R_1-3 and growth forms except, and a decrease of Th, The spectra according to the summed dominance ratio are more significant than those according to the number of species. 3) Exchanged-soil plot : -The floristic composition (Table 4) of the first year is similar to that of the second year on the burned-soil plot. The yearly change of dominants is Digitaria-Ambrosia-Artemisia-Vicia. The dominance-rank relation (Fig. 3) and composition curve (Fig. 4) seem to show a development of plant population from WILLIAMS'L-type to PRESTON'S S-type, The biological spectra (Table 5) indicate a successional change according to the increase of hypogeals, R_1-3 and 1,and the decrease of the wide spread disseminules (D_2+D_2). 4) Distribution type : -As a stochastic process in the distribution of the number of individuals in a quadrate, the POISSON type related only to the quadrate size a and the geometrical progression type related to a and the number of individuals appeared in a quadrate n are recognized (Table 6 a, b, c). The latter is also called the exponential type in the field of economic statistics. 5) Time effect and area effect : -The distribution type varies as the size of quadrate (Table 7), and varies with time(Tables 8,9)as the geometrical progression type-POISSON type-POLYAEGGENBERGER type-binominal type-normal type. These effects are called the area effect and the time effect respectively by the authors.