Date of Award:


Document Type:


Degree Name:

Master of Science (MS)


Watershed Sciences

Committee Chair(s)

Phaedra Budy


Phaedra Budy


Peter Wilcock


Casey Pennock


The rivers of the Colorado River Basin (CRB) have been degraded by human activities such flow regulation, water overallocation, and the introduction of invasive riparian vegetation (primarily tamarisk tamarix spp. and Russian olive Elaeagnus angustifolia). These stressors have resulted in widespread habitat loss and simplification, which is a major contributor to the endangerment of native fishes in the CRB.

The objectives of this study were to 1) assess the effectiveness of enhancing native fish habitat by experimentally adding cut wood from nonnative Russian olive to the San Juan River, a highly degraded dryland river, and 2) determine the magnitude of channel narrowing and vegetation encroachment over time, which are indicators of riverine habitat alteration, for three dryland CRB tributaries. Addressing these objectives can provide valuable insights to assist managers in more effectively restoring habitats for endangered native fish species.

Our results indicate that wood addition can lead to increased local abundances of native fishes, which is likely due to the increased food resources and higher habitat quality that wood addition facilitated. Additionally, we demonstrated that all three study rivers underwent substantial vegetation encroachment and channel narrowing, the latter of which coincided with a general decrease in river flows over time, with large decreases in flows corresponding to more pronounced channel narrowing. We therefore provide evidence supporting nonnative wood addition as an effective management action for enhancing native fish habitat while also underscoring the magnitude of river alteration in the region. Our findings emphasize that, when possible, preserving or restoring natural flows should be prioritized for the effective conservation of dryland rivers. In systems where managing flows is not feasible, managers may consider non-flow methods, like adding in-stream wood, to improve native fish habitats.



Creative Commons License

Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.