Abstract

A comparative study of the two Los Angeles aqueduct systems was appropriate and feasible because of the 57 year span between construction dates. Although, dealing with complex interactive relationships of a variety of parameters and some unmeasurable aspects, this project attempted to get a closer look at the impacts of man-made constructions in the Mojave Desert.

Land managers and ecologists are particularly interested in answering the questions, how did the Mojave Desert perennial vegetation respond to a utility construction, such as the Los Angeles aqueduct, and what is the intensity of damage to plant cover. The recovery rates for vegetation reestablishment is another interesting area, with great heuristic value.

This study intended to discover the quantitative and qualitative relationship of the construction of the 1913 and 1970 Los Angeles aqueduct systems to vegetation parameters of productivity, stability, and diversity. Eleven study areas were selected at intervals along the 1913 aqueduct right of way, and 15 study areas along the 1970 system. Each study area consisted of three transects; the control, right of way, and roadedge. Individual plants height and diameter were recorded for each belt transect of. 200 square meters, during the summer months of 1978.

Estimates of productivity were derived from biomass, density, ground cover, and volume measure. Diversity was evaluated from richness, evenness, equability, and a measure of diversity index. Stability was analyzed by observing percent composition and relative age Values community quality indices; and the coefficient of similarity for transects.

Qualification and quantification of vegetation along both aqueducts showed the respective constructions to have produced different effects on the parameters of productivity, diversity, and stability of the vegetation. Productivity, diversity, and stability, resulted in higher levels for the 1913 aqueduct, and seems to have recovered essentially, as far as productivity is concerned. Assuming that successional vegetative growth was linear, recovery time to predisturbance condition was estimated to be approximately 60 years for productivity, 70 years for diversity, and 1500 to 2000 years for stability. While the 1913 aqueduct right of way appears to have recovered its biomass, the percentage composition is unlike the adjacent undisturbed vegetation, indicating that much of the 1913 aqueduct right of way is sub-climax vegetation, often dominated by Chrysothamnus nauseosus ssp hololeucus. Stability results showed that, even though, the 1913 aqueduct has higher stability level than the 1970 system, there is still indication of impacts on the vegetation since construction time.

Prevalence of Cheysothamnus species along the Los Angeles aqueducts right of way may show up as an increase in productivity but decrease in stability and diversity. Further studies of the means by which Chrysothamnus nauseosus ssp hololeucus compete successfully against native shrubs, are needed for a better understanding of the plant dynamics following disturbance in Mojave Desert vegetation. It was verified that the 1913 aqueduct system presents higher levels in the considered vegetation parameters, and confirmed that time span for"recovery is the principal factor effecting this condition.

LLU Discipline

Biology

Department

Biology

School

Graduate School

First Advisor

Earl W. Lathrop

Second Advisor

Raymond E. Ryckman

Third Advisor

Robert L. Schultz

Degree Name

Master of Arts (MA)

Degree Level

M.A.

Year Degree Awarded

1980

Date (Title Page)

5-1980

Language

English

Library of Congress/MESH Subject Headings

Desertification -- California -- Mojave Desert

Type

Thesis

Page Count

vii: 112

Digital Format

PDF

Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.

Collection

Loma Linda University Electronic Theses and Dissertations

Collection Website

http://scholarsrepository.llu.edu/etd/

Repository

Loma Linda University. Del E. Webb Memorial Library. University Archives

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