Year of Award

2023

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Fish and Wildlife Biology

Department or School/College

W.A. Franke College of Forestry and Conservation

Committee Chair

Lisa A. Eby

Commitee Members

Jedediah F. Brodie, Benjamin P. Colman, Andrew R. Whiteley, Andrew C. Wilcox

Keywords

Beaver, Beaver dam analog, Beaver related restoration, Brook trout, Stream restoration, Westslope Cutthroat Trout

Publisher

University of Montana

Abstract

The importance of freshwater habitats in supporting ecological communities and human civilization is irrefutable, yet they remain amongst the most imperiled systems in the world due to factors like resource extraction, non-native species, and climate change. In the Western United States, efforts to combat stream degradation and drought have sought to increase water storage, aggrade eroded stream beds, and increase base flows by promoting dam building by beavers and through restoration projects using human-made beaver dam analogs (BDAs). Even though beaver-related restoration projects are becoming increasingly popular, documentation of the effects of beaver dams and beaver-related restoration on headwater stream habitats and biota is lacking. This information gap has generated concerns regarding the impacts of beaver-related restoration on stream temperature, invasive species, and connectivity as it pertains to native trout. In this dissertation, I integrated findings from reach scale experiments and landscape scale analyses to quantify the effects of beaver impoundments and beaver-related restoration on stream habitat characteristics and trout populations in headwater streams to help fill these knowledge gaps.

In Chapter 1, I measured the effects of BDAs on stream hydrology, temperature, and fish population demographic parameters. Investigation of the effects of BDAs across three headwater streams showed that small scale restoration projects resulted in small, short-term increases in water storage and, in some cases, buffering of stream maximum temperatures. Changes to stream habitats by BDAs did not result in significant changes in trout density, growth rates, or survival. In Chapter 2, I observed limited effects of beaver dams on stream temperature gradients relative to broader geomorphic controls while demonstrating the potential for beaver ponds to act as hot spots of non-native brook trout (Salvelinus fontinalis) and potential vectors for brook trout expansion in headwaters. Finally, I investigated the effects of beaver dams and BDAs on fish movement in Chapter 3 and found that when there is ample water, fish tend to pass dams readily. However, when dry conditions and irrigation practices interact to drop water levels rapidly, passage over BDAs can be limited. Even though native fish have persisted on the landscape for centuries with beavers, these results substantiated a few of the concerns associated with beaver impoundments and beaver-related research on a landscape dominated by drought, high water extraction, as well as non-native species. Together, this work fills several knowledge gaps that can help prioritize future beaver-related restoration projects, such as tradeoffs between restoring degraded streams and creating potential threats to native cold-water trout. This work also highlights the importance of monitoring across a range of spatial and temporal scales to evaluate beaver-related restoration.

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