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Interpreting canopy development and physiology using a European phenology camera network at flux sites

Wingate, L.; Ogee, J.; Cremonese, E.; Filippa, G.; Mizunuma, T.; Migliavacca, M.; Moisy, C.; Wilkinson, M.; Moureaux, C. and Wohlfahrt, G., et al. (2015) In Biogeosciences 12(20). p.5995-6015
Abstract
Plant phenological development is orchestrated through subtle changes in photoperiod, temperature, soil moisture and nutrient availability. Presently, the exact timing of plant development stages and their response to climate and management practices are crudely represented in land surface models. As visual observations of phenology are laborious, there is a need to supplement long-term observations with automated techniques such as those provided by digital repeat photography at high temporal and spatial resolution. We present the first synthesis from a growing observational network of digital cameras installed on towers across Europe above deciduous and evergreen forests, grasslands and croplands, where vegetation and atmosphere CO2... (More)
Plant phenological development is orchestrated through subtle changes in photoperiod, temperature, soil moisture and nutrient availability. Presently, the exact timing of plant development stages and their response to climate and management practices are crudely represented in land surface models. As visual observations of phenology are laborious, there is a need to supplement long-term observations with automated techniques such as those provided by digital repeat photography at high temporal and spatial resolution. We present the first synthesis from a growing observational network of digital cameras installed on towers across Europe above deciduous and evergreen forests, grasslands and croplands, where vegetation and atmosphere CO2 fluxes are measured continuously. Using colour indices from digital images and using piecewise regression analysis of time series, we explored whether key changes in canopy phenology could be detected automatically across different land use types in the network. The piecewise regression approach could capture the start and end of the growing season, in addition to identifying striking changes in colour signals caused by flowering and management practices such as mowing. Exploring the dates of green-up and senescence of deciduous forests extracted by the piecewise regression approach against dates estimated from visual observations, we found that these phenological events could be detected adequately (RMSE < 8 and 11 days for leaf out and leaf fall, respectively). We also investigated whether the seasonal patterns of red, green and blue colour fractions derived from digital images could be modelled mechanistically using the PROSAIL model parameterised with information of seasonal changes in canopy leaf area and leaf chlorophyll and carotenoid concentrations. From a model sensitivity analysis we found that variations in colour fractions, and in particular the late spring 'green hump' observed repeatedly in deciduous broadleaf canopies across the network, are essentially dominated by changes in the respective pigment concentrations. Using the model we were able to explain why this spring maximum in green signal is often observed out of phase with the maximum period of canopy photosynthesis in ecosystems across Europe. Coupling such quasi-continuous digital records of canopy colours with co-located CO2 flux measurements will improve our understanding of how changes in growing season length are likely to shape the capacity of European ecosystems to sequester CO2 in the future. (Less)
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Biogeosciences
volume
12
issue
20
pages
5995 - 6015
publisher
Copernicus Publications
external identifiers
  • wos:000363182200007
  • scopus:84945348954
ISSN
1726-4189
DOI
10.5194/bg-12-5995-2015
language
English
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yes
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2015-11-26 12:26:09
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@article{b8357f70-7a1f-4fba-b640-7ef5ba5c313f,
  abstract     = {Plant phenological development is orchestrated through subtle changes in photoperiod, temperature, soil moisture and nutrient availability. Presently, the exact timing of plant development stages and their response to climate and management practices are crudely represented in land surface models. As visual observations of phenology are laborious, there is a need to supplement long-term observations with automated techniques such as those provided by digital repeat photography at high temporal and spatial resolution. We present the first synthesis from a growing observational network of digital cameras installed on towers across Europe above deciduous and evergreen forests, grasslands and croplands, where vegetation and atmosphere CO2 fluxes are measured continuously. Using colour indices from digital images and using piecewise regression analysis of time series, we explored whether key changes in canopy phenology could be detected automatically across different land use types in the network. The piecewise regression approach could capture the start and end of the growing season, in addition to identifying striking changes in colour signals caused by flowering and management practices such as mowing. Exploring the dates of green-up and senescence of deciduous forests extracted by the piecewise regression approach against dates estimated from visual observations, we found that these phenological events could be detected adequately (RMSE &lt; 8 and 11 days for leaf out and leaf fall, respectively). We also investigated whether the seasonal patterns of red, green and blue colour fractions derived from digital images could be modelled mechanistically using the PROSAIL model parameterised with information of seasonal changes in canopy leaf area and leaf chlorophyll and carotenoid concentrations. From a model sensitivity analysis we found that variations in colour fractions, and in particular the late spring 'green hump' observed repeatedly in deciduous broadleaf canopies across the network, are essentially dominated by changes in the respective pigment concentrations. Using the model we were able to explain why this spring maximum in green signal is often observed out of phase with the maximum period of canopy photosynthesis in ecosystems across Europe. Coupling such quasi-continuous digital records of canopy colours with co-located CO2 flux measurements will improve our understanding of how changes in growing season length are likely to shape the capacity of European ecosystems to sequester CO2 in the future.},
  author       = {Wingate, L. and Ogee, J. and Cremonese, E. and Filippa, G. and Mizunuma, T. and Migliavacca, M. and Moisy, C. and Wilkinson, M. and Moureaux, C. and Wohlfahrt, G. and Hammerle, A. and Hoertnagl, L. and Gimeno, C. and Porcar-Castell, A. and Galvagno, M. and Nakaji, T. and Morison, J. and Kolle, O. and Knohl, A. and Kutsch, W. and Kolari, P. and Nikinmaa, E. and Ibrom, A. and Gielen, B. and Eugster, W. and Balzarolo, M. and Papale, D. and Klumpp, K. and Koestner, B. and Gruenwald, T. and Joffre, R. and Ourcival, J. -M. and Hellström, Margareta and Lindroth, Anders and George, C. and Longdoz, B. and Genty, B. and Levula, J. and Heinesch, B. and Sprintsin, M. and Yakir, D. and Manise, T. and Guyon, D. and Ahrends, H. and Plaza-Aguilar, A. and Guan, J. H. and Grace, J.},
  issn         = {1726-4189},
  language     = {eng},
  number       = {20},
  pages        = {5995--6015},
  publisher    = {Copernicus Publications},
  series       = {Biogeosciences},
  title        = {Interpreting canopy development and physiology using a European phenology camera network at flux sites},
  url          = {http://dx.doi.org/10.5194/bg-12-5995-2015},
  volume       = {12},
  year         = {2015},
}