Theses and Dissertations

Date of Award


Document Type


Degree Name

Master of Science (MS)


Agricultural, Environmental, and Sustainability Sciences

First Advisor

Dr. Bradley Christoffersen

Second Advisor

Dr. Christopher Gabler

Third Advisor

Dr. Alejandro Fierro Cabo


Increasingly frequent and severe droughts in the Lower Rio Grande Valley National Wildlife Refuge have been observed to cause large variation in species-specific mortality patterns in young seedlings, spanning 6 – 43 % mortality within the first year. To understand the underlying mechanisms behind this, we subjected seedlings of five woody semi-arid species (Celtis pallida, Forestiera angustifolia, Sideroxylon celastrinum, Phaulothalmnus spinescens, and Zanthoxylum fagara) to a point-of-no-return drought experiment in order to (1) identify potential metrics capable of predicting species wilting and mortality responses, and (2) to understand the underlying mechanisms that correspond to species drought performance. Results suggest that belowground (not aboveground) metrics of water status were the most consistent predictors of intraspecific wilting and mortality responses. Additionally, species exhibited responses that incorporated both tolerance and avoidance strategies, in tandem with initial soil water being the most important factor in determining drought performance.


Copyright 2022 Zarek Contreras. All Rights Reserved.