Remotely sensing photosynthetic phenology in evergreen needleleaf forests in Alaska and Florida

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Anneka Williams, Biology, Bowdoin College, Brunswick, ME, Jaret S. Reblin and Barry A. Logan, Biology Department, Bowdoin College, Brunswick, ME, Troy Magney, Department of Plant Sciences, University of California, Davis, Davis, CA, David R. Bowling, School of Biological Sciences, University of Utah, Salt Lake City, UT, Andrew D. Richardson, Center for Ecosystem Science and Society; School of informatics, Computing and Cyber Systems, Northern Arizona University, AZ, Zoe Pierrat and Jochen Stutz, Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, Los Angeles, CA, Christian Frankenberg, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA

Background/Question/Methods
Conifer evergreen needleleaf forests (ENF) dominate vast portions of North America and are widely distributed across the continent. The CO2 fixed via photosynthesis in high latitude, boreal ENF accounts for almost a quarter of global CO2 storage by forests, thus these forests play a significant role in the global carbon cycle. Altered seasonal fluctuations of atmospheric carbon dioxide (CO2) at high northern latitudes since the 1960’s suggest greater photosynthetic activity there as a result of anthropogenic climate change; however, the role of ENF in the observed changes remains poorly understood. Here we draw on remotely sensed measurements of photosynthetic phenology of ENF at opposite ends of the latitudinal gradient of NEON sites: Alaska and Florida. These sites represent locations that differ drastically in winter severity.
Results/Conclusions
Phenocam measurements of the green chromatic coordinate (Gcc) varied seasonally at both the FL and AK ENF sites such that values were lower in the winter and peaked during the growing season. Annual variation in Gcc was almost two-fold greater at the Alaska site than at the Florida site, while interannual variation was greater at the Florida site. Tower-based measurements of solar-induced fluorescence emission (SIF) from the Alaska site showed a marked decline during the winter months from peak values in summer. These remotely sensed measures may serve as an effective means of discerning photosynthetic phenology in ENF. Phenological trends determined from these remote measurements will be compared against leaf-level pigment composition and net ecosystem carbon exchange.