Weeds as Emerging Threat to Biodiversity:A Consequence of Spread of Ludwigia peruviana in Dhansiri and Kopili Catchment Areas of Assam, North East India

Wetlands seem to be more vulnerable to invasions compared to terrestrial ecosystems. The alien invasive weed, Ludwigia peruviana, invading the wetlands of the Dhansiri catchment and eastern part of Kopili in Assam has threatened the resident biodiversity and has also posed possibilities of spreading to other wetlands of North East India. The present study was conducted to measure the impact of the weed on the biodiversity of this region, to find out the causes for increasing invasiveness and to suggest a suitable management strategy. The weed has already damaged the marshland plant community and offered severe competition to the plants of peatland ecosystems in nearly 700 sq. km in the affected areas. Pre-monsoon temperature and monsoon rainfall had strong positive correlation with the frequency of occurrence of the weed. L. peruviana showed the highest (nearly 52%) frequency of occurrence in the wetlands of the area in comparison to other troublesome weeds. It has already formed its pure-stand in the ecotone zone replacing resident vegetation and is severely hampering normal food webs. Birds and animals either nest or graze in L. peruviana-dominant areas, and the abundant waterways exhibit high probability of spreading the weed from the gullies and furrows and settlement areas in the near future. The seriousness of the problem calls for effective and timely management strategy.