LAMBRINOS, JOHN G. Dept. of Biology, University of California, Los Angeles, Box 951606, Los Angeles, CA 90095-1606. - How dispersal characteristics and disturbance influence the expansion of the invasive pampas grass Cortaderia jubata in mediterranean plant communities of south central California.
Cortaderia jubata (Lemoine ex Carriere) Stapf is a perennial
tussock grass native to South America which was introduced into
California roughly 100 years ago and has subsequently become a major
invasive threat throughout coastal California and southern Oregon.
This study examined how two common disturbances within mediterranean
ecosystems interact with the seed dispersal and seed germination
characteristics of C. jubata to influence its expansion across
a variety of coastal habitats on Vandenberg Air Force Base, CA
(34o44'N 120o35'W).
Although on a large geographic scale C. jubata seeds have few
limits to dispersal, on a local scale seed deposition rates within
shrublands is highly structured with the greatest deposition rates
occurring in the openings between shrubs. Mechanical soil disturbance
enhances seed germination (although this effect is dependent on
habitat). In contrast, heating at high temperatures for short periods
of time and ash made from the charred stems of Artemesia
californica inhibit seed germination. These results suggest that
mechanical disturbance and wildland fire have opposite influences on
C. jubata expansion. Additionally, mechanical disturbance may
promote C. jubata expansion not only by enhancing seed
germination but also by increasing seed deposition rates.
Key words: alien, Cortaderia jubata, dispersal, disturbance, pampas grass