Response of invasive macrophyte species to drawdown: The case of Elodea sp.

The response to drawdown of vegetative fragments (whole plants, shoot fragments and turions) of two invasive macrophyte species, Elodea canadensis and Elodea nuttallii, was studied through laboratory experiments. In addition, field observations were made on the colonisation of a wetland by E. nuttallii before and after a natural drawdown. The survival and the growth of vegetative fragments of E. nuttallii were higher than those of E. canadensis after an artificial drawdown of several days. In the field the recolonisation by E. nuttallii of a wetland that was drained for 10 weeks during a summer drawdown was very rapid, the abundance of this macrophyte species being not affected by the drawdown event. We conclude that E. nuttallii possesses a high resilience to desiccation and that a summer drawdown would not be efficient in the control of this invasive species.