Award Date


Degree Type


Degree Name

Master of Science (MS)


Life Sciences

First Committee Member

Scott Abella

Second Committee Member

Stanley Smith

Third Committee Member

Philippos Tsourkas

Fourth Committee Member

Jacimaria Batista

Number of Pages



Disturbances by humans are one of the main drivers of change in contemporary desert ecosystems. Restoration treatments such as topsoil application and outplanting can be implemented in response to disturbances in order to maintain soil stability and a diverse plant community. Fertile islands - nutrient enriched areas beneath perennial shrubs - are fundamental features of deserts that can facilitate annual plant growth. A major uncertainty in desert ecology is how much time is required for fertile islands and nurse plant effects (the facilitation of one plant by another) to develop below maturing perennial plants. By studying naturally recruited perennial plants no older than age 10 years using a unique study design including sites where soils were severely disturbed, homogenized, and denuded of perennial plants 10 years earlier and comparing with undisturbed desert, this study assessed soil, annual plants, and soil seed banks beneath Ambrosia dumosa shrubs. Influences on fertile island development of the restoration treatments of applying salvaged topsoil and outplanting were also assessed. Plant cover and species richness of native plants tended to be higher in undisturbed areas, while exotic plants had higher cover in disturbed areas regardless of treatment type. The fertile island effect was prevalent below shrubs across all treatments including disturbed/unrestored, disturbed/restored, and undisturbed controls. Native and exotic plants also grew in association with the fertile island instead of in interspaces between shrubs. The soil seed bank was larger and more species-rich in fertile islands compared with interspaces. Additionally, areas that had topsoil applied contained larger soil seed banks than disturbed, unrestored sites. Topsoil reapplication may be beneficial to maintaining abundant seeds in the soil seed bank, but a whole plot analyses of vegetation cover and species richness should be conducted to determine differences in vegetation among treatment types.


Ambrosia dumosa; Fertile islands; Outplanting; Restoration; Soil seed bank; Topsoil


Environmental Sciences | Terrestrial and Aquatic Ecology

File Format


Degree Grantor

University of Nevada, Las Vegas




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