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Date of Award

Fall 2024

Document Type

Masters Thesis

Department or Program Affiliation

Environmental Sciences

Degree Name

Master of Science (MS)

Department

Environmental Sciences

First Advisor

Bunn, Andrew Godard

Second Advisor

Helfield, James M.

Third Advisor

Rybczyk, John M.

Abstract

Tree rings are a rich and abundant source of information on past climate, but ring-width measurements must typically undergo statistical standardization to become useful climate proxies. Retaining the long-term trends in growth, which offer insight into natural and anthropogenic variations in climate, remains a significant challenge during standardization. This study evaluates the performance of the ‘simple signal-free’ (SSF) standardization method, an algorithm designed to address this issue, and compares the performance against traditional standardization methods. We used simulated tree-ring studies embedded with known climate signals to assess SSF’s ability to recover these signals across different detrending settings and climate types. Our results show that SSF performs best when the study exhibits a high inter-series correlation, but its effectiveness varies across settings and climate types. A key tradeoff with SSF is the balance between increased signal capture and higher bias under the division setting, where SSF tends to introduce artificial trends or overestimate them late in the study timeline. The presence of late-study positive biases when using SSF to resolve white and red noise climate signals was particularly concerning. Traditional methods, in contrast, are generally more efficient and less prone to such biases. Under some settings, SSF was able to resolve trends that traditional methods under-captured, such as late-study positive temperature trends, but these advantages diminish under other settings, with traditional methods performing comparably or better. Results from this research should be considered when defining SSF’s default settings in current and future software libraries that offer it as a standardization method. The division setting should be avoided until future analysis can shed light on the mechanism behind its introduction of biases. While many tree-ring parameters and their range, distribution, and interdependencies were taken into consideration in the tree-ring simulator, this study is limited by the use of a simple linear model to describe tree rings and the focus on just four climate signals. Future research should include a larger range of climate signals, and tree rings should be simulated and tested using a multiplicative model. Given the variability in SSF’s performance, the ongoing debate on the best way to standardize tree-ring data while retaining low-frequency trends remains unresolved.

Type

Text

Keywords

dendrochronology, dendroclimatology, climate proxies, tree rings, standardization methods, simulation modeling, detrending, simple signal-free

Publisher

Western Washington University

OCLC Number

1473277765

Subject – LCSH

Dendrochronology; Dendroclimatology; Tree-rings--Growth--Simulation methods; Tree-rings--Growth--Computer simulation

Format

application/pdf

Genre/Form

masters theses

Language

English

Rights

Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this document for commercial purposes, or for financial gain, shall not be allowed without the author’s written permission.

Rights Statement

http://rightsstatements.org/vocab/InC/1.0/

Creative Commons License

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.

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