Using digital repeat photography and eddy covariance data to model grassland phenology and photosynthetic CO2 uptake

Mirco Migliavacca, Marta Galvagno, Edoardo Cremonese, Micol Rossini, Michele Meroni, Oliver Sonnentag, Sergio Cogliati, Giovanni Manca, Fabrizio Diotri, Lorenzo Busetto, Alessandro Cescatti, Roberto Colombo, Francesco Fava, Umberto Morra di Cella, Emiliano Pari, Consolata Siniscalco, Andrew D. Richardson

Research output: Contribution to journalArticlepeer-review

150 Scopus citations

Abstract

The continuous and automated monitoring of canopy phenology is of increasing scientific interest for the multiple implications of vegetation dynamics on ecosystem carbon and energy fluxes. For this purpose we evaluated the applicability of digital camera imagery for monitoring and modeling phenology and physiology of a subalpine grassland over the 2009 and 2010 growing seasons.We tested the relationships between color indices (i.e. the algebraic combinations of RGB brightness levels) tracking canopy greenness extracted from repeated digital images against field measurements of green and total biomass, leaf area index (LAI), greenness visual estimation, vegetation indices computed from continuous spectroradiometric measurements and CO2 fluxes observed with the eddy covariance technique. A strong relationship was found between canopy greenness and (i) structural parameters (i.e., LAI) and (ii) canopy photosynthesis (i.e. Gross Primary Production; GPP). Color indices were also well correlated with vegetation indices typically used for monitoring landscape phenology from satellite, suggesting that digital repeat photography provides high-quality ground data for evaluation of satellite phenology products.We demonstrate that by using canopy greenness we can refine phenological models (Growing Season Index, GSI) by describing canopy development and considering the role of ecological factors (e.g., snow, temperature and photoperiod) controlling grassland phenology. Moreover, we show that canopy greenness combined with radiation use efficiency (RUE) obtained from spectral indices related to photochemistry (i.e., scaled Photochemical Reflectance Index) or meteorology (i.e., MOD17 RUE) can be used to predict daily GPP.Building on previous work that has demonstrated that seasonal variation in the structure and function of plant canopies can be quantified using digital camera imagery, we have highlighted the potential use of these data for the development and parameterization of phenological and RUE models, and thus point toward an extension of the proposed methodologies to the dataset collected within PhenoCam Network.

Original languageEnglish (US)
Pages (from-to)1325-1337
Number of pages13
JournalAgricultural and Forest Meteorology
Volume151
Issue number10
DOIs
StatePublished - Oct 15 2011
Externally publishedYes

Keywords

  • Color indices
  • Digital repeat photography
  • Gross primary production
  • Growing Season Index
  • Phenology
  • Subalpine grasslands

ASJC Scopus subject areas

  • Forestry
  • Global and Planetary Change
  • Agronomy and Crop Science
  • Atmospheric Science

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