Secondary succession of weed communities in lowland habitats of Taiwan in relation to the introduction of wild-rice (Oryza perennis) populations

Abstract

Wild-rice (Oryza perennis Moench) populations were introduced into abandoned lowland fields (and a ditch) at five sites in Taiwan. The weeds arising after clearance and tillage of the fields were observed with regard to various attributes of the community during three years. Among a total of 84 identified species, Leersia hexandra had the highest relative frequency. With secondary succession, the percentage biomass of perennial species, particularly of grasses, gradually increased and the dominance index (1-H′/H′ max) also increased. Species present in the buried seed pool in soil samples showed a different pattern of successional changes. With species classified into grass, sedge, and dicot groups and their percentage of biomass data compared with corresponding data for the density of plants from buried seeds, a negative correlation was found which suggested differences in behavior among the plant groups. Experiments on the effects of weeding and inundation suggested that the niches of Oryza perennis and of Leersia hexandra largely overlap, and differed from that of Panicum repens. The wild-rice populations declined as Leersia dominated. This relationship was demonstrated by principal component analysis and standard partial regression analysis of the data.