Influence of Water Level on Torpedograss Establishment in Lake Okeechobee, Florida

ABSTRACT Lake Okeechobee, a 173,200 ha shallow subtropical lake located in south Florida, has been invaded recently by torpedograss (Panicum repens), an exotic, terrestrial species, that was intentionally introduced to Florida in the early 1900s. Since the 1970s, more than 6,000 ha of native plants, including spikerush (Eleocharis cellulose) and beakrush (Rhynchospora spp.) and open water habitat have been displaced by torpedograss in areas of the marsh where inundation depths often are less than 50 cm. The ability of torpedograss to disperse and become established at different water depths was evaluated in a series of experimental pond studies. These studies revealed that fragments remain buoyant for extended periods and so facilitate the dispersal of torpedograss within the lake. If fragments become anchored to sediment that is either exposed or in shallow water, they can readily root and establish mature plants. Once established, torpedograss can thrive in depths of 75 cm or less and can survive prolonged exposure to flooding depths greater than 1 m. In this manner, low water periods can contribute to the dispersal and colonization pattern of torpedograss in the lake. When coupled with lake elevation data, these findings suggest that low water levels or drawdowns would increase the marsh area susceptible to torpedograss invasion.