The effects of soil flooding on the establishment of cogongrass (Imperata cylindrica), a nonindigenous invader of the southeastern United States

Cogongrass (Imperata cylindrica), an invasive perennial introduced from Sou theast Asia, is currently spreading throughout the southeastern United Stat es from Florida to Louisiana. In the U.S., cogongrass is generally not cons idered a wetland species, although it's range is expanding in regions with high wetland abundance. The objective of this study was to determine if exc essive soil moisture might prevent cogongrass from establishing in areas wi th seasonally flooded soils. In one greenhouse experiment, we examined cogo ngrass germination and seedling growth in soils that were freely drained, s aturated, and inundated. We performed a second greenhouse experiment to eva luate growth and survival of cogongrass seedlings of four different size cl asses in five soil moisture treatments ranging from dry to inundated. Cogon grass germination was lowest when seeds were overtopped with water. There w ere no differences in germination between saturated and freely drained trea tments; however, seedlings grew largest in freely drained soil and were sma llest when immersed. In our second experiment, most cogongrass plants survi ved except when given no water, but growth differed by watering treatment d epending on seedling size. Increasing moisture was more detrimental to the growth of small seedlings compared to the growth of larger cogongrass plant s. Overall, cogongrass was most sensitive to soil inundation in the earlies t stages of establishment; thus, excessive moisture conditions in the sprin g, during early seedling development, could restrict invasion of cogongrass by seed. Once cogongrass is established, however, its tolerance of floodin g appears to increase.