Impact of Ageratum conyzoides L. on the diversity and composition of vegetation in the Shivalik hills of Himachal Pradesh (Northwestern Himalaya), India

The flora of the Shivalik hills of Himachal Pradesh, India is under threat due to the rapid invasion of invasive species. Invasive species means an alien species, which becomes established in natural or semi-natural ecosystems and threatens native biological diversity. In their new regimes they show diverse life forms, habit, morphology, reproductive biology, grow fast, have the ability to grow under different habitats, produce enormous number of very small, light weight seeds that and can  - survive in soil for years helping  long distance dispersal and spread. They can out-compete native species, reduce wildlife habitat potential, alter natural ecosystem processes and limit overall biodiversity. Ageratum conyzoides is one such widely adaptive weed from sub-tropical America that has entered in the Shivalik hills of Hamrpur district of Himachal Pradesh. It has grown as monocultures, in grasslands, forests, agricultural, plantations and horticultural fields in Himachal Pradesh. Hence, it was decided to evaluate the impact of A. conyzoides on the diversity and floristic compositions of native species. It was found that as compared to control, in the Ageratum invaded area; the average number of plant species has reduced by 32.10%; the a diversity has reduced by 41.21% and the dry biomass of plants has also reduced significantly. It was concluded that invasion of A. conyzoides is drastically affecting the productivity and diversity of the invaded areas in Shivalik hills of Hamirpur district.    Key words: Invasive species, biological diversity, shivalik hills.