The distribution of invasive alien plant species in peri-urban areas: a case study from the city of Kolkata

Urbanization results in rapid land transformations impacting bio-diversity and ecosystem services. With urban expansions population transition will predominantly occur in the peri-urban areas of the world’s metropolitan cities like India, China, and Nigeria, which are often located in naturally species-rich regions and highly vulnerable to plant invasions. Thus it is increasingly important to monitor the changes occurring in the floral composition in such areas. The present study was therefore conducted across peri-urban habitats of Greater Kolkata, in order to establish a baseline data on plant species richness, invasive species co-occurrence, invader dominance and understand the bio-diversity pattern. Results showed a total of 62 plant species, mostly annual herbs, belonging to 29 families constituting the species richness in the study area. Both native (53%) and alien (47%) species were almost equally distributed and invasive species (32%) represented the majority among alien species. The findings also indicate that the species pool was dominated by sparsely distributed species. The number of invasive species varied from 2 to 9 per site, with 80% of sites supporting 3 or more species. Alternanthera philoxeroides and Mikania micrantha were the most frequently occurring invasive species. Overall, M. micrantha appeared to be the dominant species with 62% of sites with a high cover (> 70%) and was found to be evenly distributed in areas. However, they pose serious threat to local bio-diversity which shows that species-specific management is needed even in the peri-urban habitats.