Articles | Volume 12, issue 22
https://doi.org/10.5194/bg-12-6637-2015
https://doi.org/10.5194/bg-12-6637-2015
Research article
 | 
23 Nov 2015
Research article |  | 23 Nov 2015

Integrated radar and lidar analysis reveals extensive loss of remaining intact forest on Sumatra 2007–2010

M. B. Collins and E. T. A. Mitchard

Abstract. Forests with high above-ground biomass (AGB), including those growing on peat swamps, have historically not been thought suitable for biomass mapping and change detection using synthetic aperture radar (SAR). However, by integrating L-band (λ = 0.23 m) SAR from the ALOS and lidar from the ICESat Earth-Observing satellites with 56 field plots, we were able to create a forest biomass and change map for a 10.7 Mha section of eastern Sumatra that still contains high AGB peat swamp forest. Using a time series of SAR data we estimated changes in both forest area and AGB. We estimate that there was 274 ± 68 Tg AGB remaining in natural forest (≥ 20 m height) in the study area in 2007, with this stock reducing by approximately 11.4 % over the subsequent 3 years. A total of 137.4 kha of the study area was deforested between 2007 and 2010, an average rate of 3.8 % yr−1.

The ability to attribute forest loss to different initial biomass values allows for far more effective monitoring and baseline modelling for avoided deforestation projects than traditional, optical-based remote sensing. Furthermore, given SAR's ability to penetrate the smoke and cloud which normally obscure land cover change in this region, SAR-based forest monitoring can be relied on to provide frequent imagery. This study demonstrates that, even at L-band, which typically saturates at medium biomass levels (ca. 150 Mg ha−1), in conjunction with lidar data, it is possible to make reliable estimates of not just the area but also the carbon emissions resulting from land use change.

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Short summary
We integrated satellite synthetic aperture radar (SAR), lidar, and forest plot data to calculate the amount and loss of above-ground biomass in remaining tall natural forests in a section of Sumatra, with quantified uncertainties. We estimate very high deforestation rates of 3.8% yr-1 and the loss of 11.3% remaining forest biomass in only 3 years. L-band SAR is valuable for penetrating cloud for deforestation analyses and for reliably estimating the carbon emissions from land use change.
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