Graduation Date
Spring 2026
Document Type
Thesis
Program
Master of Science degree with a major in Natural Resources, option Forestry, Watershed, & Wildland Sciences
Committee Chair Name
Rosemary Sherriff
Committee Chair Affiliation
Cal Poly Humboldt Faculty or Staff
Second Committee Member Name
Laura Levy
Second Committee Member Affiliation
Cal Poly Humboldt Faculty or Staff
Third Committee Member Name
Alan Tepley
Third Committee Member Affiliation
Cal Poly Humboldt Faculty or Staff
Fourth Committee Member Name
Karen King
Fourth Committee Member Affiliation
Community Member or Outside Professional
Keywords
Dendrochronology, Climate, Klamath Mountains, Reconstruction, Dendroclimatology
Subject Categories
Natural Resources
Abstract
The Trinity Alps Wilderness is a unique setting for evaluating late-Holocene climate variability because former glaciers occupied comparatively low elevations in a region influenced by both coastal and interior climate patterns. Tree-ring chronologies were developed from four conifer species—Shasta red fir (Abies magnifica var. shastensis), western white pine (Pinus monticola), Brewer’s spruce (Picea breweriana), and mountain hemlock (Tsuga mertensiana)—sampled at high elevations (1950 - 2300 m) near Emerald and Grizzly Lakes in the Trinity Alps Wilderness in northern California. The final chronologies included 12 Shasta red fir trees, 12 western white pine trees, 12 Brewer’s spruce trees, and 27 mountain hemlock trees, with chronology lengths spanning 1719 - 2023 CE, 1670 - 2023 CE, 1477 - 2023 CE, and 1550 - 2023 CE, respectively. The oldest sampled tree, a living Brewer’s spruce, dated to 1286 CE. Mean interseries correlation (Rbar) ranged from 0.50 to 0.62, indicating common growth signals within each species. Climate-growth relationships were evaluated using monthly precipitation, maximum temperature, and Palmer Drought Severity Index (PDSI) for the period 1950 - 2023 CE. Climate-growth relationships indicated that annual growth was associated with seasonal climate variability, particularly precipitation, drought conditions, and late-summer maximum temperature. The retained climate reconstructions included Shasta red fir March - October PDSI and western white pine November - April precipitation, which captured both low-frequency and year-to-year variability (R² = 0.21 - 0.30; CE = 0.10 - 0.34). In contrast, temperature reconstructions performed poorly, with negative verification statistics indicating they did not reliably reproduce temperature variability. Reconstructed records indicate decadal- to multi-decadal variability in moisture conditions, including dry conditions during the early 18th century (1707 - 1743 CE), wet conditions during the early to mid-19th century (1800 - 1860 CE), and drier conditions during the late 20th to early 21st century (1987 - 2018 CE). This study extends annually resolved climate records in the Trinity Alps and provides new insight into long-term climate variability in a complex region. These records provide context for interpreting past glacier fluctuations, recent glacier loss, and future climate sensitivity in high-elevation ecosystems of northern California.
Recommended Citation
Knepp, Emma R., "Long-term relationships between tree growth and climate in the Trinity Alps Wilderness, Klamath Mountains, California, USA" (2026). Cal Poly Humboldt theses and projects. 2569.
https://digitalcommons.humboldt.edu/etd/2569
Collaboration
1