Date of Award

8-2025

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Forest Resources

First Committee Advisor

Shawn Fraver

Second Committee Member

Andrew Ouimette

Third Committee Member

Jay Wason

Abstract

Fine woody debris (FWD; deadwood < 10cm diameter) is often overlooked as a forest carbon component, despite comprising 28% of total deadwood carbon stocks in the United States. The goal of this study was to expand our understanding of the role of FWD in the forest carbon cycle. We quantified FWD CO2 emissions from representative samples in a northern conifer forest (Maine, USA) over an extended field season (April through November, 2024). FWD wood moisture and soil temperature were the primary environmental factors influencing flux rates, while relative humidity had a moderate influence. CO2 flux varied widely throughout the season, tracking changes in soil temperature and wood moisture. Mean daily flux rates ranged from 0.3 × 10-3 to 6.6 × 10-3 μg C·g-1·s-1. We used a linear mixed-effects model to estimate flux over the growing season and found annual FWD carbon emissions to be 37.2 ± 28.0 gC·m-2·yr-1. We were unable to fully assess the potential effect of diameter on FWD flux rates, given the confounding influence of FWD moisture. FWD represented 16% of the total deadwood biomass at this site. Ultra-fine (< 1cm diameter) FWD represented a large proportion of FWD biomass and had greater wood density than that of larger diameter FWD. Accurate models of forest carbon dynamics rely on these measurements of local-scale FWD stocks and CO2 fluxes.

In northeastern North America, episodic eastern spruce budworm (Choristoneura fumiferana) outbreaks commonly defoliate balsam fir (Abies balsamea) and spruces (Picea glauca, P. rubens, P. mariana). We investigated budworm defoliation in eastern hemlock (Tsuga canadensis), a purported alternate host species, during previously documented outbreaks in Maine, USA. We compiled red spruce and hemlock tree-ring series from nine sites, eight of which showed radial growth reductions in both spruce and hemlock during documented budworm outbreaks. Outbreak evidence varied among sites, but the 1914 outbreak was observed in seven study sites. Synchronous growth reductions between spruce and hemlock suggested that when budworm defoliation occurred in spruce at a given site, hemlock experienced at least some level of defoliation. Moderate synchrony in budburst phenology between species may contribute to hemlock’s suitability as an alternate host. This research is timely given the recent spruce budworm population increase in the region.

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