author = "Toomey, M. and Friedl, M. A. and Frolking, S. and Hufkens, K. and 
                         Klosterman, S. and Sonnentag, O. and Baldochhi, D. D. and 
                         Bernacchi, C. J. and Biraud, S. C. and Bohrer, G. and Brzostek, E. 
                         and Burns, S. P. and Coursolle, C. and Hollinger, D. Y. and 
                         Margolis, H. A. and McCaughey, H. and Monson, R. K. and Munger, J. 
                         W. and Pallardy, S. and Phillips, R. P. and Torn, M. S. and 
                         Wharton, S. and Zeri, Lui Marcelo de Mattos and Richardson, A. 
          affiliation = "{Harvard University} and {Department of Earth and Environment} and 
                         {University of New Hampshire} and {Ghent University} and {Harvard 
                         University} and {Universit{\'e} de Montre{\'a}l} and {University 
                         of California} and {University of Illinois at Urbana-Champaign} 
                         and {Lawrence Berkeley National Laboratory} and {Ohio State 
                         University} and {Indiana University} and {University of Colorado} 
                         and {Universit{\'e} Laval} and {USDA Forest Service} and 
                         {Universit{\'e} Laval} and {Queen's University} and {University 
                         of Arizona} and {Harvard University} and {University of Missouri} 
                         and {Indiana University} and {Lawrence Berkeley National 
                         Laboratory} and {Lawrence Livermore National Laboratory} and 
                         {Instituto Nacional de Pesquisas Espaciais (INPE)} and {Harvard 
                title = "Greenness indices from digital cameras predict the timing and 
                         seasonal dynamics of canopy-scale photosynthesis",
              journal = "Ecological Applications",
                 year = "2015",
               volume = "25",
               number = "1",
                pages = "99--115",
                month = "Jan.",
             keywords = "Deciduous broadleaf forest, Digital repeat photography, Evergreen 
                         needleleaf forest, Grassland, Gross primary productivity, 
                         PhenoCam, Phenology, Photosynthesis, Seasonality.",
             abstract = "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.",
                 issn = "1051-0761",
             language = "en",
        urlaccessdate = "02 dez. 2020"