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Thesis Abstract – Caspi (2018)

Title:

Effects of invasive annuals on soil C and N storage along a coast to inland gradient in southern California

Author and college:

Tal Caspi, Scripps College

Date:

April 2018

Degree:

Bachelor of Arts in Environmental Science

Advisors:

Wallace Meyer, Biology Department, Pomona College
Colin Robins, Keck Science Department of Claremont McKenna, Pitzer, and Scripps Colleges

Abstract:

Non-native plant invasions are threats to biodiversity, yet the impact of invasions on nutrient cycling processes, particularly in soil, are often overlooked. In southern California, California sage scrub (hereafter sage scrub), the native shrub-dominated habitat type in lowland areas, has decreased to < 10% of its original distribution mainly due to type-conversion to non-native annual grasslands. Preliminary studies suggest that type-conversion negatively impacts C storage, but our ability to predict the consequences of widespread type-conversion on regional nutrient budgets remains limited. By assessing how composition of the invading plant community, microbial abundance, and soil conditions impact storage capacity in surface soils of adjacent native and invasive habitat types at nine sites along a coast to inland gradient, we identified key factors controlling regional soil C and N storage. The impact of type-conversion on nutrient storage was contingent upon the identity of the invader. Sage scrub stored more C and N than non-native grassland habitats, but sites with non-native habitats dominated by Brassica spp. had nutrient concentrations that were similar to sage scrub. Across the gradient, we found that total C and N increased in sites with high cation exchange capacities and bacterial concentrations and decreased with pH, which was higher in invasive habitats. We calculate that > 925 t C km^-2 and > 60 t N km^-2 are lost when sage scrub converts to grass-dominated habitat, indicating that non-native grass invasions are a significant regional contributor to greenhouse gas emissions. We provide a new predictive framework for modeling regional nutrient storage that incorporates fine-scale information on soil cation exchange capacity, accurate classification of invasive habitat types, and quantification of bacterial abundance.

For more information:

Contact Colin Robins – crobins@kecksci.claremont.edu