INVASION OF Parthenium hysterophorus. L. WEED OVER OTHER COMMON WEEDS IN THE VAVUNIYA DISTRICT, SRI LANKA

Abstract

Parthenium is a highly invasive weed in Sri Lanka which was initially reported in Vavuniya district and intensely affected the environment. Therefore, this study was carried out to assess the invasion of Parthenium weed of the other weeds in the urban and suburban areas of Vavuniya district. A field survey was carried out to quantify the distribution of Parthenium and other species composition at 21 locations where Parthenium infestation was reported. At each sampling location 05 experimental quadrats with Parthenium infestation and five control quadrats without Parthenium infestation over different land use types (e.g: agricultural lands, village tanks, associated lands, road sides and barren lands) were used to study the variation in the association of native floral species in Parthenium dominated locations. Invasive Alien Species (IAS) provincial profile map of Vavuniya District, Northern Province was used as the secondary data for this study. The Shannon diversity index (H) was used to characterize the species diversity of weeds. Parthenium in the study area was noticed to have higher Absolute Density (AD), i.e., 2 plants per square meter whilst Tephrosia purpurea (0.3), Cleome viscose (0.25), Ocimum canum (0.35) were identified with moderate AD. The rest of the species, such as Tridax procumbens, Leucas zeyianica, Mimosa pudica, Calotropis gigantean, Amaranthus spinasus, Emillia javanica, Stachytarpheta jamaicensis, Lantana camera, Dichrostach cinerea, and Vernonia cinerea showed values less than 0.25. The Relative Density (RD) of the Parthenium weed was recorded as the highest (~26%) whilst the rest were less than 11%. Accordingly, Parthenium was the most dominant IAS in the study area and it appears to suppress the growth of the other species. The quadrats lacking Parthenium observed with the well distribution of the other species. The species richness and species evenness of Parthenium was found to be in the range of 0.36–0.72 and 0.60-0.98 respectively. Infestation of the Parthenium was higher in the Vavuniya town area where the rainwater usually collects.