PARENT SESSION
Tuesday, August 8, 1:30-5:00 pm
COS 44 - Grassland ecology II
Heritage Ballroom IV, Marriott
Presiders: J Ely

Native perennial bunchgrass resistance to invasion by Foeniculum vulgare (fennel) in a California coastal grassland.

Abraham, Joel^*,1, Corbin, Jeffery¹, D'Antonio, Carla², ¹ University of California, Berkeley, Berkeley, CA² University of California, Santa Barbara, Goleta, CA

ABSTRACT- The conversion of California grasslands from native perennial bunchgrass to exotic annual grass dominated systems has caused both seasonal and spatial changes in resource availability. These changes are largely driven by species trait differences, and may influence the future invasibility of the community. This study examines the relative resistance of native perennial versus exotic annual grasses to colonization by Foeniculum vulgare, an invasive European perennial herb. We hypothesized that native perennial grasses would suppress F. vulgare germination and growth relative to exotic annual grass or bare plots because of their more consistent coverage of the soil surface and greater reduction in resource availability. We tested these hypotheses in coastal northern CA, in experimental plots of native perennial grasses (Nassella pulchra, Festuca rubra, Agrostis oregonensis), exotic annual species (Bromus diandrus, Vulpia myorus, Avena barbata,) or bare soil, maintained since 1998. We added locally collected F. vulgare seeds to each plot, and measured abundance, average height, and average leaf number of plants, from late winter through early summer in 2004. We also measured ambient and soil surface photosynthetically active radiation (PAR) levels in each plot. We also conducted a germination trial to directly test the effect of reduced PAR on F. vulgare. As predicted, F. vulgare seedlings were more abundant in bare and annual plots than in perennial plots. Seedling height and leaf number, however, were similar in perennial and annual treatments, although larger in bare plots. PAR during the germination period was positively correlated with F. vulgare seedling abundance; perennial dominated plots had significantly lower PAR levels at the soil surface level. Annual grass dominated systems may be less resistant to invasion by F. vulgare than established native perennial grasslands; this reduced resistance may also apply to other exotic or colonizing native perennials/winter annual herbs that have similar resource requirements or phenology.

Key words: California grasslands, Foeniculum vulgare, biological invasions