Introduction

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Diagram describing structural characteristics of the tropical peat swamp forest that impact scattering signals and associated metrics included in this study (adapted from Kasischke and Bourgeau-Chavez [33]).

Diagram describing structural characteristics of the tropical peat swamp forest that impact scattering signals and associated metrics included in this study (adapted from Kasischke and Bourgeau-Chavez [33]).</p

Diagram depicting sources of scattering from inundated forests (adapted from Kasischke and Bourgeau-Chavez [33]).

Scattering mechanisms in bold represent scattering sources that result in interferometric fringes.</p

Fig 5 -

Maps presenting processed optical and LiDAR data, describing above-ground biomass structure and peat swamp surface characteristics, including (a) LAI (leaf area index per 20 m2); (b) LiDAR ground point density (ground point number per 10 m2); (c) ROUGH; (d) WD; (e) VDR. All LiDAR-derived datasets are limited to the LiDAR flight line coverage over North Selangor. Base map provided by OpenStreetMap®. OpenStreetMap® is open data, licensed under the Open Data Commons Open Database License (ODbL) by the OpenStreetMap Foundation (OSMF). OpenStreetMap® is made available under the Open Database License: http://opendatacommons.org/licenses/odbl/1.0/. Any rights in individual contents of the database are licensed under the Database Contents License: http://opendatacommons.org/licenses/dbcl/1.0/.</p

Photographs illustrating common land cover types and field conditions at north Selangor.

(a) secondary forest, (b) burned peatland with dense grass and shrubs, (c) rice paddy agriculture and (d) oil palm plantation. (Photo credits: MJL).</p

PCA visualising the relationship between <i>coherence count</i> (cohcount) values and metrics describing the canopy, trunk and surface layers in the model of the above-ground biomass stand: LAI (canopy openness), ROUGH (canopy roughness), WD (height of forest stand), VDR (ratio of canopy layer to trunk layer) and GPD (exposure of peat swamp forest surface).

Plots represent all 2-dimensional combinations of the first three Principal Components: (a) PC1 and PC2, (b) PC1 and PC3, (c) PC2 and PC3. All three plots show that coherence count is orthogonal to all other variables.</p

Fig 6 -

Sentinel-1 interferograms and coherence maps for North Selangor: a) VV polarisation from 2/7/2017 to 17/7/2017; b) VH polarisation from 2/7/2017 to 17/7/2017; c) VV polarisation from 14/8/2018 to 14/8/2018; d) the VH polarisation from 14/8/2018 to 14/8/2018. Base map provided by OpenStreetMap®. OpenStreetMap® is open data, licensed under the Open Data Commons Open Database License (ODbL) by the OpenStreetMap Foundation (OSMF). OpenStreetMap® is made available under the Open Database License: http://opendatacommons.org/licenses/odbl/1.0/. Any rights in individual contents of the database are licensed under the Database Contents License: http://opendatacommons.org/licenses/dbcl/1.0/.</p

Fig 7 -

(a) Map of coherence counts (cohcount) of interferometric pairs at 20 m resolution between 10/10/2014 and 29/04/2020. The coherence count represents the number of interferometric pairs that are above the coherence threshold of 0.45 (maximum = 1520). (b) Map of land cover for North Selangor. Study of both maps show that coherence counts remained high over forestry within North Selangor relative to other land cover types. Base map provided by OpenStreetMap®. OpenStreetMap® is open data, licensed under the Open Data Commons Open Database License (ODbL) by the OpenStreetMap Foundation (OSMF). OpenStreetMap® is made available under the Open Database License: http://opendatacommons.org/licenses/odbl/1.0/. Any rights in individual contents of the database are licensed under the Database Contents License: http://opendatacommons.org/licenses/dbcl/1.0/.</p

North Selangor reserve boundary and peatland extent located within Selangor, Peninsular Malaysia, SE Asia.

Base map provided by OpenStreetMap®. OpenStreetMap® is open data, licensed under the Open Data Commons Open Database License (ODbL) by the OpenStreetMap Foundation (OSMF). OpenStreetMap® is made available under the Open Database License: http://opendatacommons.org/licenses/odbl/1.0/. Any rights in individual contents of the database are licensed under the Database Contents License: http://opendatacommons.org/licenses/dbcl/1.0/.</p

Exploring Spatial Patterns of Tropical Peatland Subsidence in Selangor, Malaysia Using the APSIS-DInSAR Technique

Tropical peatlands in Southeast Asia have experienced widespread subsidence due to forest clearance and drainage for agriculture, oil palm and pulp wood production, causing concerns about their function as a long-term carbon store. Peatland drainage leads to subsidence (lowering of peatland surface), an indicator of degraded peatlands, while stability/uplift indicates peatland accumulation and ecosystem health. We used the Advanced Pixel System using the Intermittent SBAS (ASPIS-DInSAR) technique with biophysical and geographical data to investigate the impact of peatland drainage and agriculture on spatial patterns of subsidence in Selangor, Malaysia. Results showed pronounced subsidence in areas subjected to drainage for agricultural and oil palm plantations, while stable areas were associated with intact forests. The most powerful predictors of subsidence rates were the distance from the drainage canal or peat boundary; however, other drivers such as soil properties and water table levels were also important. The maximum subsidence rate detected was lower than that documented by ground-based methods. Therefore, whilst the APSIS-DInSAR technique may underestimate absolute subsidence rates, it gives valuable information on the direction of motion and spatial variability of subsidence. The study confirms widespread and severe peatland degradation in Selangor, highlighting the value of DInSAR for identifying priority zones for restoration and emphasising the need for conservation and restoration efforts to preserve Selangor peatlands and prevent further environmental impacts