Predicting the spread of alligator weed (Alternanthera philoxeroides) in Wular lake, India: A mathematical approach

Alligator weed (Alternanthera philoxeroides) is an amphibious weed invading worldwide. It was reported very recently from Wular lake, a Ramsar site in India. The weed forms isolated floating islands of variable sizes in this lake. Monitoring of the weed for 4 years reveals that the total number of patches increased from 6 in 2008 to 82 in 2011 with total area of all patches increasing from 41.3 m2 in 2008 to 831 m2 in 2011. We did predictive modeling with four years data using a variable growth rate equation, to estimate the spread rate of the weed assuming the entire lake area available for spread. Our model suggests that this weed may potentially cover entire lake in 13-19 years from 2008. The robustness of the mathematical model was also determined and validated using data from the first three years and it was in coherence with the previous model. We do caution, the predictive spread model of A. philoxeroides presented here has a strong bearing to the uncertainties of climate change, nutrient loading and competition effects. The study warrants an urgent need for rapid action involving manual removal before it actually assumes bigger dimensions in the lake and the region as more than ten thousand households completely depend on the resources of Wular lake, India.