Water level effects on growth of Melaleuca seedlings from Lake Okeechobee (Florida, USA) littoral zone

The invasive exotic wetland tree, Melaleuca quinquenervia, is expanding rap idly throughout seasonally wet areas of southern Florida (USA), including t he littoral zone of Lake Okeechobee. Natural resource managers are concerne d that a lower lake level regulation schedule under consideration for Lake Okeechobee, while potentially beneficial to overall ecosystem health, might increase the rate of Melaleuca expansion. To investigate this possibility, Melaleuca saplings (harvested from the littoral zone) and 7-week-old seedl ings (grown from harvested seeds) were subjected to various hydroperiod tre atments in replicated mesocosms. hydroperiod treatments were selected based on a simulation of historical water level variations. Saplings grew taller under longer hydroperiods with fluctuating water levels, including periods of submersion. Time Since germination affected the response of seedlings t o inundation. Submersed 7-week-old seedlings grew slower and had less bioma ss than submersed 12-week-old seedlings, yet mortality was low at both ages . Melaleuca's plasticity allows it to adapt to hypoxic, aquatic conditions by means of aquatic heterophylly and adventitious roots. Algae and drought also increased mortality. Based on faster growth of Melaleuca under longer hydroperiods and its adaptability to seasonal flooding. a lower lake regula tion schedule may not stimulate its expansion. Therefore, water levels shou ld not be manipulated only to control Melaleuca. Control of Melaleuca shoul d continue using current practices such as manual removal or chemical treat ment.