Year of Graduation
2021
Level of Access
Open Access Thesis
Embargo Period
5-20-2026
Department or Program
Biology
First Advisor
Barry Logan
Abstract
Conifer forests play an important role in the global carbon cycle by assimilating carbon dioxide (CO2), but monitoring the seasonality (i.e. phenology) of photosynthesis in these forests is challenging. Recent studies suggest the utility of measuring changes in canopy coloration and spectral signatures to monitor conifer forest photosynthetic phenology. I performed a latitudinal site comparison of canopy coloration measured with the green chromatic coordinate (Gcc), derived from repeat digital photography, between conifer forests in Alaska (DJEU) and Florida (OSBS). OSBS demonstrated more interannual variability in Gcc while DEJU showed greater annual variation, most likely as a product of consistently lower temperatures at DEJU than at OSBS. Snow on the canopy had a significant effect on Gcc at DEJU, suggesting the importance of visual image inspection when working with Gcc measurements. I also performed a within-site analysis of solar-induced fluorescence (SIF) and explored the alignment of Gcc and SIF with gross primary productivity (GPP) measured by eddy covariance techniques at the Alaska (DEJU) site. Gcc, SIF, and GPP exhibited a general alignment at the DEJU site, however, limitations in data availability and an overly heavy dependence on so-called data “gap-filling” make it hard to predict the start-of-season (SOS) and end-of-season (EOS) transition dates. My work suggests the potential for Gcc and SIF to serve as remote measures of photosynthetic phenology, which would expand our ability to monitor photosynthesis by allowing us to assess forests in locations not suitable to the eddy covariance technique of GPP calculations.