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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 13, issue 19
Biogeosciences, 13, 5587-5608, 2016
https://doi.org/10.5194/bg-13-5587-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: OzFlux: a network for the study of ecosystem carbon and water...

Biogeosciences, 13, 5587-5608, 2016
https://doi.org/10.5194/bg-13-5587-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 07 Oct 2016

Research article | 07 Oct 2016

MODIS vegetation products as proxies of photosynthetic potential along a gradient of meteorologically and biologically driven ecosystem productivity

Natalia Restrepo-Coupe1, Alfredo Huete1, Kevin Davies1,7, James Cleverly2, Jason Beringer3, Derek Eamus2, Eva van Gorsel4, Lindsay B. Hutley5, and Wayne S. Meyer6 Natalia Restrepo-Coupe et al.
  • 1Plant Functional Biology and Climate Change Cluster, University of Technology Sydney, P.O. Box 123, Broadway, NSW 2007, Australia
  • 2School of Life Sciences, University of Technology Sydney, P.O. Box 123, Broadway, NSW 2007, Australia
  • 3School of Earth and Environment, The University of Western Australia, Crawley, WA 6009, Australia
  • 4CSIRO Oceans and Atmosphere, Forestry House, Building 002, Wilf Crane Crescent, Yarralumla, ACT 2601, Australia
  • 5Research Institute for the Environment and Livelihoods, Charles Darwin University, Darwin, NT 0909, Australia
  • 6Environment Institute, School of Biological Sciences, University of Adelaide, Adelaide, SA 5005, Australia
  • 7School of Geosciences, University of Sydney, Sydney, NSW 2006, Australia

Abstract. A direct relationship between gross ecosystem productivity (GEP) estimated by the eddy covariance (EC) method and Moderate Resolution Imaging Spectroradiometer (MODIS) vegetation indices (VIs) has been observed in many temperate and tropical ecosystems. However, in Australian evergreen forests, and particularly sclerophyll and temperate woodlands, MODIS VIs do not capture seasonality of GEP. In this study, we re-evaluate the connection between satellite and flux tower data at four contrasting Australian ecosystems, through comparisons of GEP and four measures of photosynthetic potential, derived via parameterization of the light response curve: ecosystem light use efficiency (LUE), photosynthetic capacity (Pc), GEP at saturation (GEPsat), and quantum yield (α), with MODIS vegetation satellite products, including VIs, gross primary productivity (GPPMOD), leaf area index (LAIMOD), and fraction of photosynthetic active radiation (fPARMOD). We found that satellite-derived biophysical products constitute a measurement of ecosystem structure (e.g. leaf area index – quantity of leaves) and function (e.g. leaf level photosynthetic assimilation capacity – quality of leaves), rather than GEP. Our results show that in primarily meteorological-driven (e.g. photosynthetic active radiation, air temperature, and/or precipitation) and relatively aseasonal ecosystems (e.g. evergreen wet sclerophyll forests), there were no statistically significant relationships between GEP and satellite-derived measures of greenness. In contrast, for phenology-driven ecosystems (e.g. tropical savannas), changes in the vegetation status drove GEP, and tower-based measurements of photosynthetic activity were best represented by VIs. We observed the highest correlations between MODIS products and GEP in locations where key meteorological variables and vegetation phenology were synchronous (e.g. semi-arid Acacia woodlands) and low correlation at locations where they were asynchronous (e.g. Mediterranean ecosystems). However, we found a statistical significant relationship between the seasonal measures of photosynthetic potential (Pc and LUE) and VIs, where each ecosystem aligns along a continuum; we emphasize here that knowledge of the conditions in which flux tower measurements and VIs or other remote sensing products converge greatly advances our understanding of the mechanisms driving the carbon cycle (phenology and climate drivers) and provides an ecological basis for interpretation of satellite-derived measures of greenness.

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We re-evaluated the connection between satellite greenness products and C-flux tower data in four Australian ecosystems. We identify key mechanisms driving the carbon cycle, and provide an ecological basis for the interpretation of vegetation indices. We found relationships between productivity and greenness to be non-significant in meteorologically driven evergreen forests and sites where climate and vegetation phenology were asynchronous, and highly correlated in phenology-driven ecosystems.
We re-evaluated the connection between satellite greenness products and C-flux tower data in...
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