PARENT SESSION
Oral Session #19: Plant Competition. Presiding: N. Slade.
Monday, August 6, 2001. 1:00 PM to 5:15 PM. Hall of Ideas J.
Temporal variation in competitive interference between annual and perennial grasses.
Corbin, Jeffrey1, D'Antonio, Carla1, 1
ABSTRACT- The persistence of the California annual grassland system is compelling evidence that annual grasses, though not native to the region, enjoy competitive advantages over the formerly dominant native perennial bunchgrasses. A number of studies have shown the negative impact that competitive interference from non-native annuals has on perennial grasses. We hypothesized, however, that perennial bunchgrasses, once established beyond the first year, enjoy advantages that would negatively affect annual grass productivity in subsequent years. In 1998, we established replicate "communities" consisting of three species of native perennial grasses, three species of non-native annual grasses, and both the native perennial and non-native annual grasses together. Perennials were grown from seed in the greenhouse and transplanted to the field as small seedlings; annual grasses were cast as seed. The presence of annuals negatively affected the above-ground growth of native perennial grasses in all three growing seasons. While the presence of perennials had no significant impact on the above-ground production of annuals in year 1, interference from perennial grasses strongly negatively affected the above-ground productivity of annuals in yrs 2 and 3. In addition to reducing the annuals' productivity, the perennial grasses reduced the density of annuals, the biomass of other weedy invaders and reduced light penetration to the soil surface. We suggest that management practices that reduce above-ground biomass of native perennial grasses increase the success of invading annuals in these habitats.
KEY WORDS: California grassland, plant competition, annual grasses, perennial bunchgrasses