Effects of Parthenium Weed (Parthenium hysterophorus L.) on Biodiversity of Native Plant Species in Nakuru County, Kenya

Abstract

Invasive Alien Species (IAS) are organisms that are introduced into new areas where they establish and have adverse effects on the environment and human livelihoods. Worldwide IAS are considered the second most serious threat to biodiversity after habitat destruction. Among the notable IAS in Kenya is parthenium weed (Parthenium hysterophorus L.). Parthenium hysterophorus is an annual plant native to South and Central America considered to occur as an invasive invader in Africa, Asia and Australia. It is one of the worst weeds because it produces allelochemicals which inhibit the germination and growth of other species resulting in habitat change. In Kenya, high colonies of the weed are threatening the existence of native plant species, especially in the western, Lake Victoria Basin and the Rift Valley. Therefore, this study investigated the effects of P. hysterophorus on the biodiversity of native plant species in Nakuru County, Kenya. The study was carried out in Gilgil sub-county using the quadrants method whereby all the herbaceous plants were counted and identified. Data on the effects of P. hysterophorus on the density of native plant species was analyzed using correlation analysis at a 1 % level of significance. The Shannon-Weiner Diversity Index and Evenness Index were used to determine species diversity. The results of this study established that high densities of P. hysterophorus significantly reduced the abundance of the native plant species (r = -0.367, p = 0.001). It was also established that the presence of P. hysterophorus in the study area lowered the diversity of native plant species according to the low values of both the Shannon-Weiner Diversity Index (1.78) and Evenness Index (0.20085). According to the results of this study, P. hysterophorus significantly lowered both the diversity and abundance of the native plant species in the study. Therefore, urgent control measures should be put in place to avert further damage to the vegetation cover which is likely to compromise the availability of pasture species in a county whose main activities include agriculture. In addition, the findings of this research can be used to inform policy formulation on invasive weed control in Kenya.