Articles | Volume 12, issue 22
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.

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.
Final-revised paper