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Can a satellite-derived estimate of the fraction of PAR absorbed by chlorophyll (FAPAR) improve predictions of light-use efficiency and ecosystem photosynthesis for a boreal aspen forest?

Summary

Published in Remote Sensing of Environment 113: 880-888 https://doi.org/10.1016/j.rse.2009.01.002

We used daily MODerate resolution Imaging Spectroradiometer (MODIS) imagery obtained over a five-year period to analyze the seasonal and inter-annual variability of the fraction of absorbed photosynthetically active radiation (FAPAR) and photosynthetic light use efficiency (LUE) for the Southern Old Aspen (SOA) flux tower site located near the soutern limit of the boreal forest in Saskatchewan, Canada. To obtain the spectral characteristics of a standardized land area to compare with tower measurements, we scaled up the nominal 500 m MODIS products to a 2.5 km x 2.5 km area (5 x 5 MODIS 500 m grid cells). We then used the scaled-up MODIS products in a coupled canopy-leaf radiative transfer model, PROSAIL-2, to estimate the fraction of absorbed photosynthetically active radiation (APAR) by the part of the canopy dominated by chlorophyll (FAPARchl) versus that by the whole canopy (FAPARcanopy). Using the additional information provided by flux tower-based measurements of gross ecosystem production (GEP) and incident PAR, we determined 90-minute averages for APAR and LUE (slope of GEP:APAR) for both the physiologically active foliage (APARchl, LUEchl) and for the entire canopy (APARcanopy, LUEcanopy).

The flux tower measurements of GEP were strongly related to the MODIS-derived estimates of APARchl (r2=0.78) but only weakly related to APARcanopy (r2=0.33). Gross LUE between 2001 and 2005 for LUEchl was 0.0241 mmol C mmol-1 PPFD whereas LUEcanopy was 36% lower. Time series of the 5-year normalized difference vegetation index (NDVI) were used to estimate the average length of the core growing season as days of year 152-259. Inter-annual variability in the core growing season LUEchl (mmol C mmol-1 PPFD) ranged from 0.0225 in 2003 to 0.0310 in 2004. The five-year time series of LUEchl corresponded well with both the seasonal phase and amplitude of LUE from the tower measurements but this was not the case for LUEcanopy. We conclude that LUEchl derived from MODIS observations could provide a more physiologically realistic parameter than the more commonly used LUEcanopy as an input to9 large-scale photosynthesis models.

Sector(s): 

Forests

Categorie(s): 

Scientific Article

Theme(s): 

Ecosystems and Environment, Forest Ecology, Forestry Research, Forests

Departmental author(s): 

Drolet, Guillaume

Author(s)

ZHANG, Qingyuan, Elizabeth M. MIDDLETON, Hank A. MARGOLIS, Guillaume G. DROLET, Alan A. BARR and T. Andrew BLACK

Year of publication :

2009

Format :

Paper

Keywords :

peuplier faux-tremble, chlorophylle, productivité primaire brute, efficacité d'utilisation de la lumière, écologie écosystèmes et environnement, écosystèmes et environnement, article scientifique de recherche forestière, MODIS, Populus tremuloides, FAPARchl, ecosystems and environment, aspen, chlorophyll, gross primary production, light use efficiency, LUE

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