Impact of the invasive weed Ageratum conyzoides in the Shivalik Ranges of the north-western Himalayas, India.
Abstract
The number of species, plant density and vegetation biomass were studied in various habitats invaded by (billy goat weed, BGW Ageratum conyzoides), i.e. uninvaded control, invaded grasslands, invaded plantation of Dalbergia sissoo, invaded riparian zone, and invaded wastelands. In addition, residues collected from BGW-infested areas were mixed into soil (1g/100 soil) from BGW-free areas, and the impact of these soils on early seedling growth and biomass accumulation of Cassia tora was studied. Compared with controls, native vegetation in BGW-infested habitats was significantly reduced, including number of species, plant density and biomass, especially in wastelands and grasslands, indicating that invasion by BGW greatly affects the structure and composition of natural vegetation and reduces plant diversity. Following invasion by BGW, large quantities of plant residues accumulated, which eventually decomposed and became mixed with the soil. Such residues had negative effect on the seedling growth and biomass accumulation of C. tora. The BGW residues were found to contain 470 mg phenolics per 100 g, which was considered responsible for the allelopathic effect on C. tora.
