Award Date

5-1-2019

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Life Sciences

First Committee Member

Scott Abella

Second Committee Member

Lloyd Stark

Third Committee Member

Dale Devitt

Fourth Committee Member

Brenda Buck

Number of Pages

120

Abstract

The Mojave and Sonoran Deserts have been negatively impacted by anthropogenic disturbances. Considering that these ecosystems may recover on millennial timescales, research has shown that restoration techniques can be fairly successful in initiating long-term recovery processes in these sensitive environments. However, uncertainty remains as to which techniques are effective in different circumstances, such as in different climates or across different soil properties, and which techniques may best avoid unintended consequences, such as facilitating non-native plants. To reduce fugitive dust as a human health hazard, increase soil stability, and enhance wildlife habitat, further work is necessary to develop restoration techniques for disturbed desert landscapes. The aims of this thesis were to examine the impacts of severe disturbances on soils of the Mojave and Sonoran Deserts and to investigate the efficacy of target restoration techniques within these ecoregions. Studies were conducted in the field, laboratory, and greenhouse to determine how anthropogenic disturbances impact soil characteristics and test the effectiveness of the three implemented restoration techniques.

The target restoration techniques chosen for this study span varying levels of effort and financial cost to better understand how effective minimal-input restoration strategies are in contrast to costlier, more intensive strategies. The minimal-input techniques examined here included vertical mulch (placing dead branches upright in the soil to simulate the appearance of dead shrubs), soil surface manipulations (such as surface de-compaction and contouring the soil to create water catchments), outplanting, and seeding with litter. My research analyzes the effectiveness of vertical mulch treatments, surface de-compaction, and seeding with litter in the Dead Mountains Wilderness Area located 18 km northwest of Needles, CA in the Mojave Desert. I analyzed the influence of vertical mulch, water catchments, and outplanting in four distinct study sites south of Joshua Tree National Park along the Devers Palo II Transmission Corridor from Indio, CA to Blythe, CA. I conducted laboratory analyses of soil conditions at each of the sites. Before establishing restoration treatments in both regions, soil conditions were characterized by a lack of natural recovery of native perennial vegetation, and lower vegetation cover in disturbed sites in comparison to undisturbed sites.

Among the treatments at the Dead Mountains site, vertical mulch yielded the highest plant cover, soil moisture, soil stability, and lowest compaction in the Dead Mountains sites. During the wetter year of the survey, the surface de-compaction treatment had similar, less apparent results, indicating that surface de-compaction may be an alternative to vertical mulch if managers do not require vertical mulch structures to prevent public use of disturbed areas. These trends were not mirrored in the Devers Palo II Transmission Line sites, which had highly variable data, potentially due to the soil characteristics of each of the four sites. Each site had distinct bulk density, soil texture, pH, electrical conductivity, and C/N ratios that may have caused variability in the soil and plant responses to restoration treatments. The sites with the highest clay, silt, and organic matter had the highest plant cover and soil moisture whereas the site with the most mobile, well-drained soils had the lowest. Soil accumulation was highest in the vertical mulch treatments among all sites. Outplanting was largely unsuccessful due to the seedlings dying within four months of planting but may have had legacy effects, such as de-compacting the soil, inputting nutrients, and forming vertical mulch. These findings suggest that soil conditions may have been a stronger driver of soil and vegetation variation than restoration treatments.

The collected data suggest that the effects of vertical mulch surpass visual effects to include ecological ones. Vertical mulch and, to a lesser degree, soil de-compaction are a viable restoration treatments to reduce soil erosion and increase plant cover. However, the degree of restoration success depends upon soil conditions, indicating that a contextual understanding of study sites is necessary for overall success. This thesis can help inform restoration activities within arid lands, which are increasingly threatened by human-induced disturbances.

Keywords

Mojave Desert; Restoration ecology; Revegetation; Soil surface manipulation; Sonoran Desert; Vertical mulch

Disciplines

Biology | Environmental Sciences | Soil Science | Terrestrial and Aquatic Ecology

Language

English


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