Abstract
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.
Highlights
Tropical forests provide multiple ecosystem services such as climate regulation and water filtration (Naidoo et al, 2008)
We have demonstrated for the first time that it is possible to employ a fusion of synthetic aperture radar (SAR), lidar, and forest plot data to map above-ground biomass (AGB) and its change across a tropical forest landscape
This was enabled by the establishment of robust relationships between (i) AGB and Lorey’s height estimates from field plots and (ii) HV backscatter and Lorey’s height estimates from lidar data, which increases by 2 orders of magnitude the number of observations of Lorey’s height which we have from the 56 forest plots alone
Summary
Tropical forests provide multiple ecosystem services such as climate regulation and water filtration (Naidoo et al, 2008). DD in developing countries accounts for between 7 and 20 % of anthropogenic CO2 emissions, e.g. 18 % (Grace et al, 2014), 15 % with a range of 8–20 % (van der Werf et al, 2009), and 7–14 % (Harris, 2012). This is leading to between 0.9 and 2.2 Pg C yr−1 being transferred to the atmosphere (Houghton, 2010). In the private sector, investors and consumers are pressuring companies trading in commodities like soy, palm oil, and timber
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