Abstract
In order to analyze the effect of paddy field reconstruction on the biological environment, the vegetation on four kinds of levees surrounding different types of paddy fields, namely traditionally managed levees, levees of paddy fields reconstructed 10 years ago, levees of paddy fields reconstructed 6 years ago, and levees of paddy fields reconstructed in the previous year was investigated in Sakai city, Osaka. The composition of the plant species in the vegetation on the flat and sloping parts of the levees was monitored by the total estimation method 8 times with one month intervals from April to December in 1997. On the flat part of the levees the average number of species per levee ranged from 35 to 36 in four kinds of levees. However species composition was different among the levee types (Table 2). On the sloping part of the levees, the average number of species per levee ranged from 29 to 38 and the species composition was different in the four levees (Table 3). On traditionally managed levees, domestic perennial species dominated, and annual and alien species were seldom observed. On the levees of the paddy fields reconstructed 10 years ago and 6 years ago, alien perennial species such as Solidago altissima became dominant with the lapse of time from paddy field reconstruction.
The plant diversity on the traditionally managed levees was stable (Fig. 1) though that of the levees of the paddy fields reconstructed 10- and 6-years ago declined remarkably when mowing was practiced (Fig. 2, 3). On the traditionally managed levees, the complex plant-community structure may be maintained with a high plant diversity. On the levees of the paddy field reconstructed 10- and 6-years ago, a simple plant-community structure resulted in a lower plant diversity when mowing was practiced.
It is suggested that the vegetation on the levees of the paddy fields reconstructed 10- and 6-years ago may undergo a successional process different from the usual process in the vegetation of traditionally managed levees (Fig. 5, 6).
