Comment on ‘A first map of tropical Africa’s above-ground biomass derived from satellite imagery’

Mitchard, E.T.A.; Saatchi, S.S.; Lewis, S.L.; Feldpausch, T.R.; Gerard, F.F.; Woodhouse, I.H.; Meir, P.. 2011 Comment on ‘A first map of tropical Africa’s above-ground biomass derived from satellite imagery’. Environmental Research Letters, 6 (4), 049001. 6, pp.

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We present a critical evaluation of the above-ground biomass (AGB) map of Africa published in this journal by Baccini et al (2008 Environ. Res. Lett. 3 045011). We first test their map against an independent dataset of 1154 scientific inventory plots from 16 African countries, and find only weak correspondence between our field plots and the AGB value given for the surrounding 1 km pixel by Baccini et al. Separating our field data using a continental landcover classification suggests that the Baccini et al map underestimates the AGB of forests and woodlands, while overestimating the AGB of savannas and grasslands. Secondly, we compare their map to 216 000 × 0.25 ha spaceborne LiDAR footprints. A comparison between Lorey’s height (basal-area-weighted average height) derived from the LiDAR data for 1 km pixels containing at least five LiDAR footprints again does not support the hypothesis that the Baccini et al map is accurate, and suggests that it significantly underestimates the AGB of higher AGB areas. We conclude that this is due to the unsuitability of some of the field data used by Baccini et al to create their map, and overfitting in their model, resulting in low accuracies outside the small areas from which their field data are drawn.

Item Type: Publication - Article
Digital Object Identifier (DOI):
Programmes: CEH Topics & Objectives 2009 - 2012 > Biogeochemistry > BGC Topic 1 - Monitoring and Interpretation of Biogeochemical and Climate Changes > BGC - 1.4 - Develop innovative, effective methods for monitoring fluxes, exposure and effects
UKCEH and CEH Sections/Science Areas: Reynard
ISSN: 1748-9326
Additional Information. Not used in RCUK Gateway to Research.: Open Access article - click on the Official URL link for full text
Additional Keywords: aboveground biomass, Africa, AGB, carbon, GLAS, LiDAR, MODIS, random forest, regression tree, remote sensing, savanna, tropical forest
NORA Subject Terms: Ecology and Environment
Date made live: 07 Nov 2011 15:06 +0 (UTC)

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