Exploring Linkages Between Remotely Sensed Canopy Nitrogen and Albedo in U.S. and Canadian Forests
Terrestrial ecosystems influence the Earth's climate through a variety of processes involving exchanges of matter and energy with the atmosphere. Using data from remote sensing, field measurements and eddy flux towers, we recently demonstrated that two important mechanisms of climate regulation, uptake of CO2 and total shortwave surface albedo, are strongly correlated and co-vary with the nitrogen status of plant canopies (%N). Specifically, we found that (1) much of the variability in canopy nitrogen (%N) is related to simple but previously unrecognized reflectance properties in the near infrared region; (2) mean canopy %N for the footprint areas around each flux tower is positively and significantly correlated with canopy-level photosynthetic capacity; and (3) canopy %N is significantly and positively correlated with total shortwave albedo. Although these findings have important implications for ecosystem-climate interactions, the specific mechanisms driving the observed linkages remain unclear. For example, although canopy %N and albedo are significantly correlated, other canopy traits such as LAI and canopy structure could underlie the observed trends. Here, we explore the basis for these relationships by incorporating additional field and remote sensing measurements and by expanding the dataset to include sites from the Canadian Carbon Program. The combined data set represents a wide range of forest types, stand ages, climate conditions and disturbance regimes. Results are discussed with respect to local variation at individual sites as a means of understanding mechanisms responsible for the observed carbon-nitrogen-albedo trends.
EOS, Transactions American Geophysical Union, Fall Meeting, Supplement
American Geophysical Union Publications
Plourde, L., Ollinger, S., Richardson, A., Martin, M., Hollinger, D. and Frolking, S. (2008), Exploring Linkages Between Remotely Sensed Canopy Nitrogen and Albedo in U.S. and Canadian Forests, Eos Trans. AGU, 89(53), Fall Meet. Suppl., Abstract B51A-0357.