Journal
ECOLOGICAL APPLICATIONS
Volume 25, Issue 1, Pages 99-115Publisher
WILEY
DOI: 10.1890/14-0005.1
Keywords
deciduous broadleaf forest; digital repeat photography; evergreen needleleaf forest; grassland; gross primary productivity; PhenoCam; phenology; photosynthesis; seasonality
Categories
Funding
- USDA Forest Service's Northeastern States Research Cooperative
- National Science Foundation's Macro-system Biology Program [EF-1065029]
- U.S. National Park Service Inventory and Monitoring Program
- USA National Phenology Network from the United States Geological Survey [USGS] [G10AP00129]
- National Science Foundation [DEB-1114804]
- USDA Forest Service's Northern Research Station
- Office of Science Biological and Environmental Research (BER), U.S. Department of Energy
- BER as part of the Atmospheric Radiation Measurement program and Atmospheric System Research program [DE-AC02-05CH11231]
- BER [DE-SC0006708]
- NSF [DEB-0911461]
- Canadian Foundation for Climate and Atmospheric Sciences (CFCAS)
- NSERC
- Natural Resources Canada
- Environment Canada
- Direct For Biological Sciences [1114804] Funding Source: National Science Foundation
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The proliferation of digital cameras co-located with eddy covariance instrumentation provides new opportunities to better understand the relationship between canopy phenology and the seasonality of canopy photosynthesis. In this paper we analyze the abilities and limitations of canopy color metrics measured by digital repeat photography to track seasonal canopy development and photosynthesis, determine phenological transition dates, and estimate intra-annual and interannual variability in canopy photosynthesis. We used 59 site-years of camera imagery and net ecosystem exchange measurements from 17 towers spanning three plant functional types (deciduous broadleaf forest, evergreen needleleaf forest, and grassland/crops) to derive color indices and estimate gross primary productivity (GPP). GPP was strongly correlated with greenness derived from camera imagery in all three plant functional types. Specifically, the beginning of the photosynthetic period in deciduous broadleaf forest and grassland/crops and the end of the photosynthetic period in grassland/crops were both correlated with changes in greenness; changes in redness were correlated with the end of the photosynthetic period in deciduous broadleaf forest. However, it was not possible to accurately identify the beginning or ending of the photosynthetic period using camera greenness in evergreen needleleaf forest. At deciduous broadleaf sites, anomalies in integrated greenness and total GPP were significantly correlated up to 60 days after the mean onset date for the start of spring. More generally, results from this work demonstrate that digital repeat photography can be used to quantify both the duration of the photosynthetically active period as well as total GPP in deciduous broadleaf forest and grassland/crops, but that new and different approaches are required before comparable results can be achieved in evergreen needleleaf forest.
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