Canopy Nitrogen, Carbon Assimilation and Surface Reflectance features in U.S. Forest Ecosystems
Scott
V
Ollinger, University of New Hampshire, scott.ollinger@unh.edu
(Presenting)
David
Y
Hollinger, US Forest Service, david@hypatia.unh.edu
Mary
E
Martin, University of New Hampshire, mary.martin@unh.edu
Andrew
D
Richardson, University of New Hampshire, andrew.richardson@unh.edu
Steve
E
Frolking, University of New Hampshire, steve frolking@unh.edu
Lucie
C
Plourde, University of New Hampshire, lucie.plourde@unh.edu
Peter
B
Reich, University of Minnesota, preich@umh.edu
In the study of terrestrial carbon cycling, developing methods by which leaf, plant and stand level processes can be related to landscapes, regions and continents represents an important challenge and is a core component of the North American Carbon Program. The ability to seamlessly transfer information across a continuum of spatial scales from field studies to Earth observing satellites would greatly improve our understanding of how vegetation, the carbon cycle and the Earth's climate interact and change over time in response to human activities and natural forcings.
Here, we report on an effort that examines the degree to which carbon assimilation in forests can be related to both local and regional variation in canopy nitrogen. Field measurements collected at forested research sites within the AmeriFlux network were combined with hyperspectral remote sensing data from the AVIRIS and Hyperion instruments. The resulting coverages were used to relate tower-based estimates of carbon assimilation capacity to canopy %N for the local landscapes surrounding each tower. Results indicate a strong and positive relationship between canopy %N and canopy-level photosynthetic capacity. Although canopy N detection has traditionally focused on narrow-band spectral features, we also found strong correlations with simpler and widely available reflectance properties and with shortwave surface reflectance estimates from MODIS. Our findings indicate that high nitrogen ecosystems have more reflective canopies, absorb less radiant energy and fix more carbon than their low N counterparts. If these patterns can be shown to exist more broadly, our results suggest an unrecognized feedback in the Earth’s climate system involving the nitrogen cycle as a moderator of carbon cycling and surface energy exchange under changing environmental conditions.
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