Detection of Forest Cover Disturbances Using Synthetic Aperture Radar (SAR) Time Series Data in the Mount Pulag National Park: A Key Biodiversity Area in Luzon, Philippines

Abstract

Forest cover disturbances continue to occur at a very alarming rate, which greatly contributes to the loss of biodiversity resources. Therefore, an approach to detect and measure historical deforestation would be of utmost importance – particularly in the near real-time forest monitoring and management, biodiversity conservation, and estimation of carbon emissions. This study introduced a simple approach using synthetic aperture radar (SAR) time-series data, primarily the C-band Sentinel-1A (S1A) VH-polarization with a 10-m resolution, in detecting forest cover disturbances from 2016–2019 in Mount Pulag National Park (MPNP), a protected area (PA) within the island of Luzon and a priority biodiversity conservation area. The process involved using codes in Google Earth Engine (GEE) to produce a forest cover disturbance map; a grid-based geospatial and statistical analysis using the geographic information system; and data validation, and determination of possible causes of disturbances using Google Earth Pro (GEP). The results derived from Sentinel-1 data were also compared to existing optical data, which is a Landsat-based generated disturbance map. The output of this paper revealed that a total of 577 forest disturbances, with an equivalent area of 154.58 ha, were detected from a three-year period. For Landsat-generated data, 402 disturbances were detected with an area of 176.07 ha. However, based on the accuracy assessment using positive predictive value (PPV), the radar data produced higher accuracy (80%) compared to the optical data (73%). The visual observation and interpretation of satellite imageries made it clear that the primary drivers of forest cover disturbances in Mount Pulag are agricultural expansion (48%), forest clearings (26%), landslides (12%), slash-and-burn or “kaingin” (12%), and forest fires (2%).