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Mikania micrantha, a creeper and climber, has invaded forests and agricultural areas in the Western Ghats. A quantification of the effect of Mikania on species richness and factors that contribute to its success would help to understand the invasion success of Mikania in the Western Ghats of India. This study investigated its impact on species richness and factors that contribute to its invasion success. Impact of Mikania on species richness was studied in areas invaded by Mikania and not yet invaded by Mikania by quadrat (1 × 1 m) method. Growth experiments were carried out with Mikania rhizosphere soil and soil treated with Mikania leaf leachate. Chemical characteristics such as electrical conductivity, organic matter, extractable P, total organic N and water-soluble phenolics, and microbial respiration of soil invaded by Mikania and not yet invaded by Mikania were measured. We observed lower species richness in areas invaded by Mikania compared to areas not yet invaded by Mikania. Seedling growth was suppressed in Mikania rhizosphere soil or soil treated with higher levels of Mikania leaf leachate. Higher levels of organic matter, total organic N and water-soluble phenolics, and lower microbial activity were observed in Mikania rhizosphere soil. Soil treated with Mikania leaf leachate has higher amounts of water-soluble phenolics. Mikania invasion appears to reduce plant species richness in the Western Ghats, and discourage seedling growth of certain plant species. Factors that are likely to contribute to Mikania success are its ability to pre-empt light and alter soil chemistry and biochemistry in ways that benefit the species. [ABSTRACT FROM AUTHOR]