The effects of gap size and disturbance type on invasion of wet pine savanna by cogongrass, Imperata cylindrica (Poaceae)

Cogongrass is a nonindigenous species perceived to threaten native communit ies of the southeastern United States through modification of species compo sition and alteration of community processes. To examine how gap size and d isturbance type influence the invasion of wet pine savannas by cogongrass, we performed three field experiments to evaluate the response of cogongrass seeds and transplanted seedlings to four different gap sizes, four types o f site disturbance, and recent burning of savanna vegetation. Cogongrass ge rminated, survived, and grew in all gap sizes, from 0 to 100 cm in diameter . Similarly, disturbance type had no effect on germination or seedling and transplant survival. Tilling, however, significantly enhanced transplanted seedling growth, resulting in a tenfold increase in biomass over the other disturbance types. Seedling survival to 1 and 2 mo was greater in burned sa vanna than unburned savanna, although transplant survival and growth were n ot affected by burning. Results of this study suggest that cogongrass can g erminate, survive, and grow in wet pine savanna communities regardless of g ap size or type of disturbance, including burning. Burning of savanna veget ation may enhance establishment by improving early seedling survival, and s oil disturbance can facilitate invasion of cogongrass by enhancing plant gr owth.