PARENT SESSION
Poster Session # 16: Invasive Species.
Wednesday, August 6 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.
Seedling recruitment and seed bank densities across ecotones betwen coastal sage scrub and grassland.
Nenzen, Hedvig*,1, Swift, Cheryl*,1, 1 Whittier College, Whittier, CA
ABSTRACT- Local patterns of plant community distribution are a function of disturbance regime, microclimate, soil type and biota, seed dispersal, seedling recruitment and competition. Coastal sage scrub often occurs as patches within a matrix of native perennial grasses, and non-native invasive annuals and annual grasses in the Puente Hills in southeastern Los Angeles County. The matrix of patches of coastal sage scrub and native grasses is typical of undisturbed coastal sage scrub as is the matrix of coastal sage scrub and non-native annuals; however, the factors responsible for the maintenance of the boundaries between these patches are not well understood. This study compared the ability of shrubs, perennial grasses, and non-native annuals to invade across shrub-native grassland and shrub-invasive grassland ecotones. Coastal sage scrub and native grasses rarely penetrated more than 1 m across the ecotone; however, invasive grasses and annuals penetrated more than 5 m into coastal sage scrub. The ability of invasive grasses and annuals to invade coastal sage scrub is correlated with the amount of bare ground present within the coastal sage scrub patch. The results of this study suggest that in the absence of invasive, the large-scale disturbance shifted the boundary between coastal sage scrub and grassland. However, when invasive annuals are present, small disturbances leading to patches of bare ground within the larger coastal sage scrub patch are easily invaded by invasive annuals leading to fine scale fragmentation within the coastal sage scrub patch. These results also suggest that invasive annuals produce seeds that disperse farther in higher numbers than native shrubs or grasses. This is confirmed by an examination of the seed banks across ecotones since invasive seeds penetrate at least 15 m into coastal sage scrub patches.
Key words: invasive species, coastal sage scrub, native grassland