Graduate Directory

Summary of Expertise

Field Botany

Plant Physiological Ecology

Research Interests

            The Mojave Desert is home to several charismatic and culturally significant species of the genus Yucca. These species, the Joshua tree (Yucca brevifolia Engelm.; Agavaceae) and the Mojave Yucca (Yucca schidigera Roezl ex Ortgies), both have tremendous economic importance to local human communities, ecological significance to local natural communities, and cultural significance that extends well beyond their growing range. Both of these species are also under threat by human factors. The Joshua tree, a species whose range is nearly concurrent with and whose image is synonymous with the Mojave Desert, may be restricted to small refugia within its current range by the end of the century. The Mojave Yucca, a stalwart of the southern desert, has become a popular source of saponins and is facing increasing harvest pressure in its distribution in Northern Baja California. This dissertation will shed light on the life-histories and stressors facing these captivating, other-worldly plants.

            In the case of the Joshua tree, the main factor that will limit their distribution in the future is their ability to obtain and manage water. As yet, no one has studied the role of water storage in Joshua tree water budgets, nor whole-plant water use in response to precipitation pulses. Although the ecological damage of the Mojave yucca has been anecdotally documented, no one has yet identified the major players in this industry or the extent of the damage. This dissertation will attempt to fill in some of these gaps.

            In Chapter 1, I will investigate the potential role of root water storage in the Joshua tree water budget. In Chapter 2, I will construct a model of whole-plant water use and try to understand how precipitation pulses of various sizes impact the Joshua tree water budget. In Chapter 3, I will attempt to explore and document the Mojave yucca supply chain and its environmental consequences through the lens of transaction cost economics.

Honors, Awards and Grants

Received Mildred Mathais Grant 2019

Received Meter Group Grant A. Harris Fellowship 2020

Selected Publications

Loik, M. E., Lesage, J. C., Brown, T. M., & Hastings, D. O. 2019. Drought‐Net rainfall shelters did not cause nondrought effects on photosynthesis for California central coast plants. Ecohydrology, e2189, 1–9. https://doi.org/10.1002/eco.2138

Evens, J. M., K. G. Sikes, J. S. Ratchford, and D. Hastings. 2015. Vegetation Classification and Mapping at Lake Mead National Recreation Area, Final Report. Natural Resource Data Series NPS/MOJN/NRDS—2015. National Park Service, Fort Collins, Colorado.

Evens, J. M., K. Sikes, D. Hastings, and J. Ratchford. 2014. Vegetation Alliance Descriptions for Lake Mead National Recreation Area, Death Valley National Park and Mojave National Preserve. Unpublished Report submitted to USDI, National Park Service, Mojave Desert Network Inventory and Monitoring Program. California Native Plant Society, Sacramento, CA.

Taylor, S., D. Hastings, J. Ratchford, J. Evens, and K. Sikes. 2014. Vegetation Mapping of Eastman and Hensley Lakes and Environs, Southern Sierra Nevada Foothills, California. Unpublished Report. California Native Plant Society, Sacramento, CA.