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 α 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

Status, invasiveness and environmental threats of three tropical American invasive weeds (Parthenium hysterophorus L., Ageratum conyzoides L., Lantana camara L.) in India

Invasive weeds have threatened the integrity of ecosystems throughout the world. They affect not only the species diversity of native areas but also their biological integrity. In India, a number of invasive exotic weeds have been reported but some viz. Parthenium hysterophorus, Lantana camara and Ageratum conyzoides, especially those from tropical America are troublesome and have caused adverse ecological, economic and social impact. These weeds can be seen growing in different landscapes but are luxuriantly localized in unattended forests and cultivated areas. Parthenium hysterophorus (Asteraceae, commonly known as congress grass) is perhaps the most troublesome and noxious weed of urban and rural India. Besides rapidly colonizing areas replacing the native vegetation, it is also known to cause a number of human health problems such as skin allergy, rhinitis and irritation to eyes of the residents in the vicinity. Likewise, it causes fodder scarcity in addition to being unpalatable and toxic to livestock. Lantana camara (Verbenaceae), another serious tropical American pest, has encroached upon large areas of land, especially the forests where it has virtually replaced the forest floor vegetation and reduced tree growth. Also because of its bushy and spreading type of growth it obstructs forest operations. The third weed, Ageratum conyzoides (Asteraceae, Billy goat weed) has invaded agricultural fields. It interferes with crops and causes yield reductions of major staple crops of India. When it invades rangeland areas, it out competes native grasses causing scarcity of fodder. These weeds have similar growth strategies such as fast growth rates, short life-cycles, greater reproductive potential, high competitive abilities and allelopathy that make them successful invaders of native habitats. Mechanical, chemical, biological and cultural control tactics have failed individually, though integrated approaches combining all these approaches along with community participation and proper land management have been relatively successful. This paper presents various aspects of biology, ecology, hazards and control measures of these weeds

Impact of invasive plants on the structure and composition of natural vegetation of Northwestern Indian Himalayas

Himachal Pradesh situated in the lap of northwestern Himalayas is one of the richest repositories of plant diversity in India. However, during the past three decades, because of the increased pace of development and interference of humans through introduction of invasive exotics, the ecology of the state has changed tremendously. Ragweed parthenium, billy goat weed, and lantana-the three exotics from South America-have caused much harm in the state because of their invasive potential. A study conducted to assess the changes in the structural composition and dynamics of vegetation shows that density and diversity of native flora were adversely affected because of invasion by these three exotics. Because all the three exotic weeds are known to exhibit allelopathy, it might be one of the major nonresource-based hypothesis for the successful invasion by these exotic species