Date of Award:

12-2023

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Watershed Sciences

Committee Chair(s)

Edward Hammill

Committee

Edward Hammill

Committee

Janice Brahney

Committee

Phaedra Budy

Committee

Joe Wheaton

Committee

Karen Beard

Abstract

Streams, rivers, and their floodplains throughout the world are impaired due to human modifications. Recent research has demonstrated that restoration projects prioritizing the proper functioning of ecosystems have better restoration outcomes than projects which focus on restoring form alone. Throughout North America, beaver-mediated restoration is becoming a leading method for improving the functioning of stream ecosystems that are in a degraded state. In areas where beaver are absent or the habitat is too degraded to currently permit their dam building, man-made beaver dam analogs (BDAs) are being used to restore stream habitat with an eye to future beaver recolonization. However, few studies have been published on BDAs. We do not currently understand how BDAs may impact threated or endangered species, no studies have investigated how close BDAs maintained by humans come to emulating natural beaver complexes, and no published works have examined BDAs’ impacts within an urban or semi-urban landscape. My research goal was to aid in filling these knowledge gaps. I determined that beaver dams influence the spawning locations of threatened Bull trout (Salvelinus confluentus) using microchips implanted into fish and redd counts in two streams. While Bull trout spawned below beaver dams more often than random chance, they continued using the same habitat that was below that dams once they were experimentally breached to allow for fish to swim past them. Next, I examined the likelihood that amphibians would breed within natural beaver complexes versus BDA complexes. I determined natural beaver complexes had a higher chance of being used for breeding, due in large part to their lower relative abundance of fishes, older age, and position within the watershed. Finally, I examined the impacts of BDA restoration to a stream ecosystem within a rapidly urbanizing watershed. I determined that BDAs were providing increased rates of sediment deposition, deeper pools, better habitat for juvenile fishes, improved growth rates in trout, and enhanced productivity within the riparian zone relative to their control reaches. However, the “positive control” of a natural beaver dam complex outperformed the beaver dam analogs in several of these metrics.

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