Role of Fire in the Germination Ecology of Fountain Grass (Pennisetum setaceum), an Invasive African Bunchgrass in Hawai'i

Field and laboratory studies were carried out to test factors expected to be relevant for the germination of fountain grass: (1) light; (2) emergence of fountain grass seedlings from depths of 0, 2.5, and 5 cm; (3) fire passing over exposed and buried seeds; (4) laboratory heat treatment mimicking exposure to grass fire. Both fire in the field and heat applied in the laboratory killed fountain grass seeds. In the laboratory, some seeds were killed after exposure to 75 degrees C for 3 min, and all seeds were killed at 100 degrees C. During the prescribed burns, temperatures at the soil surface reached at least 204 degrees C, but temperatures at depths of 2.5 and 5 cm showed no measurable change. Light is not essential for germination of fountain grass seeds, and seedlings can emerge from depths of at least 5 cm. Both of these traits contribute to the invasive capacity of the species. Because fountain grass seeds are killed at temperatures in excess of 100 degrees C, the species depends on its ability to resprout and quickly set seed after fire for population growth and spread. Seeds buried beneath the soil may escape exposure to fire, and substrate heterogeneity may provide refuge from temperature extremes experienced during fire. The morphology of fountain grass seeds likely inhibits burial in the soil for the most part, but there are several potential burial mechanisms. Prescribed burns could prove to be a useful tool for fountain grass control in large, degraded sites where fountain grass has invaded but only when coupled with additional control measures.