Date of Award

Summer 8-18-2023

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Ecology and Environmental Sciences

Advisor

Hamish Greig

Second Committee Member

John Kocik

Third Committee Member

Jasmine Saros

Additional Committee Members

Joe Zydlewski

Abstract

Ecological restoration is an increasingly common practice across ecosystems, and current practices aim to restore the biological and physical processes underlying ecosystem function, often for the sake of endangered higher-level consumers. Studies of restoration outcomes often report few or inconsistent ecological changes, and monitoring of restoration projects rarely measures ecological processes. Monitoring also usually measures outcomes at a single scale, despite the prevalence of scale- dependent phenomena across ecosystems. My thesis uses measurements of ecological processes to assess restoration response and evaluates responses across multiple scales. I focus here on a long-term large wood addition project on the Narraguagus River of eastern Maine that aims to restore habitat for Atlantic salmon (Salmo salar). Like many river restoration projects, this one involves the addition of two types of large wood structures to mimic natural treefall and the physical (e.g., scour and fill) and biological (e.g., provision of habitat, retention of detrital resources) processes fallen trees support. My research asks whether a) wood addition has any generalizable or site-specific effects, b) structure type affects ecosystem response, and c) responses differ at local (site) vs regional (50-100m reach) scales in response metrics including algal biomass, leaf breakdown rate, salmon parr prey item biomass, and various taxonomic and functional metrics of macroinvertebrate community composition. I found few generalizable ecological responses to wood additions. Site identity alone was a strong predictor of most ecological processes and macroinvertebrate community measures. Some metrics, such as leaf breakdown rate and algal biomass, showed site by treatment interactions, wherein site ID modified the response to large wood additions, but these interactions were not consistent across seasons. The two primary structure types differed in total macroinvertebrate abundance, leaf breakdown rate, and algal biomass, but again this was not consistent across seasons. It is not obvious what specific site characteristics are driving these strong site-specific responses to wood additions, though site mean macroinvertebrate taxonomic richness was predicted by site mean substrate index. However, at the regional (50-100m reach) scale, I found that the concentration of log structures is important for fine detrital and macroinvertebrate response. Total macroinvertebrate abundance was predicted by the number of structures 50m and 100m of a site. It is common practice to consider larger-scale constraints limiting ecological potential when designing restoration projects, but my research indicates that small-scale, local conditions may be just as important, as my sites differed more from each other than did treatments. In other cases, site conditions moderated ecosystem response. Finally, it is important to consider multiple scales when monitoring restoration outcomes. In this case, the number of wood additions upstream of a sampling site (regional intensity) had a much stronger influence on ecosystem metrics than the presence of wood in the immediate site area (local). Especially in a highly connected system such as a river, restoration attempts at one location may affect the response to modifications at another site nearby, or a high concentration of projects might have an interactive, rather than additive, ecological effects.

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