Abstract

Alaska is warming at a much faster rate than any other state in the USA. Average annual temperatures have already risen 1.6°C within the last century and are projected to rise by an additional 2.2°C to 3.3°C by 2070 even with a low emission scenario (Stewart et al., 2013). Due to excessive warming, Columbia Glacier has witnessed a catastrophic retreat of 20km since 1980. This has raised questions of how the forest, located in proximity to the glacier will respond, since glaciers have a cooling effect on the surrounding environment.

In this study, four tree chronologies of mountain hemlock (Tsuga mertensiana) at different elevations in Columbia Bay, Alaska, were sampled for dendroclimatic analysis. The ring width index (RWI) of each tree ring chronology was correlated with CRU TS 4.05 climate variables on KNMI Climate Explorer. The analysis revealed strong negative correlations for two sites (Heather Island and Greater Nunatak) with minimum temperature and cloud fraction, particularly, during the spring and summer months indicating that trees are adversely reacting to higher minimum temperatures. In addition, Rock Tor experienced strong negative correlations to precipitation during the winter months. The negative relationship between minimum temperature and cloud fraction with RWI suggests that increased cloudiness inhibits photosynthesis during the day and exacerbates respiration at night by trapping longwave radiation at night keeping night time temperature high. Another potential explanation could be that higher temperatures allow larger cone crops of mountain hemlock trees to mature, drawing away energy required for radial growth.

These observations were also recorded by other tree ring chronologies in Southeast Alaska an indication that the positive phase of the (Pacific Decadal Oscillation) PDO is most likely responsible for a change in growth. Meanwhile, the retreat of Columbia Glacier seems to have played little to no effect on mountain hemlock trees in Columbia Bay.

Advisor

Agarwal, Vibhor

Department

Earth Sciences

Publication Date

2023

Degree Granted

Bachelor of Arts

Document Type

Senior Independent Study Thesis

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