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Thesis Abstract – Rossman (2010)


Shrub Vigor and Allelopathy as Determinants of Invasion Resistance in Coastal Sage Scrub Habitat

Author and college:

Allison Rossman, Pomona College


May, 2010


Bachelor of Arts in Biology


Frances Hanzawa, Pomona College


Due to fire suppression in some coastal sage scrub habitats, dominant native shrubs of Artemisia californica range in vigor, from actively growing to senescent, meaning they are large and old with little new growth. A potential consequence of the aging of the plant community is a decrease in the ability of the native plants to resist invasion by non-natives by using allelopathy, a phenomenon in which active tissues in plants release chemicals that inhibit the growth of other plants. I hypothesized that the lack of new growth in senescent shrubs leads to decreased allelochemicals and an increase in the susceptibility of the habitat to invasion. By planting non-native Brassica nigra and Vulpia myuros seeds in pots in the field and in field soil in growth chambers, I examined the differences in germination and growth between soils from under senescent shrubs and active shrubs. And by treating field soil with activated carbon in the laboratory, I explored the differences in allelopathy. I found that the early growth of both non-native species is higher in senescent soil, thus potentially increasing the vulnerability of senescent communities to invasion. Allelochemicals do inhibit growth of the nonnatives, and more so in soil from under active shrubs, showing that allelopathy is a mechanism at work in increasing the vulnerability of senescent plant communities to invasion.

For more information:

Contact Frances Hanzawa – frances.hanzawa@pomona.edu

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