Date of Award

9-2020

Document Type

Thesis

Degree Name

Master of Science in Earth and Environmental Sciences

Department

Biology

First Reader/Committee Chair

Kimberlyn Williams

Abstract

Non-native annual plant species have degraded California Sage Scrub and chaparral and present obstacles to shrubland restoration. Red soil patches in chaparral and California Sage Scrub of San Bernardino and Riverside counties appear to support fewer non-native annual plants than non-red soils. The purpose of this study was to confirm differences in vegetation cover between red and non-red soils in shrublands and to use soil analyses to determine possible causes. During vegetation surveys conducted in April of 2018, it was confirmed that red soil sites had lower cover of non-native plants and higher cover of native plant species than the non-red soils. Greenhouse experiments with one non-native annual, Bromus rubens, indicated that this grass grew poorly on red soils when compared to growth on non-red soils. An initial soil analysis of several critical plant nutrients did not explain the difference in plant growth. However, an analysis of the supply rate of nutrients over a period of five months suggested that phosphate availability was more limited on red soils. Additionally, the red soils had a lower percentage of sand when compared to non-red soils. It is possible that further research may lead to potential management options that can restore native shrublands by impeding the success of non-native annual species.

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