Continuous Detection of Forest Loss in Vietnam, Laos, and Cambodia Using Sentinel-1 Data

Stéphane Mermoz,Thuy Le Toan,Thierry Koleck,Alexandre Bouvet,Marie Ballère

doi:10.3390/rs13234877

Abstract

In this study, we demonstrate the ability of a new operational system to detect forest loss at a large scale accurately and in a timely manner. We produced forest loss maps every week over Vietnam, Cambodia, and Laos (>750,000 km2 in total) using Sentinel-1 data. To do so, we used the forest loss detection method based on shadow detection. The main advantage of this method is the ability to avoid false alarms, which is relevant in Southeast Asia where the areas of forest disturbance may be very small and scattered and detection is used for alert purposes. The estimated user accuracy of the forest loss map was 0.95 for forest disturbances and 0.99 for intact forest, and the estimated producer’s accuracy was 0.90 for forest disturbances and 0.99 for intact forest, with a minimum mapping unit of 0.1 ha. This represents an important step forward compared to the values achieved by previous studies. We also found that approximately half of forest disturbances in Cambodia from 2018 to 2020 occurred in protected areas, which emphasizes the lack of efficiency in the protection and conservation of natural resources in protected areas. On an annual basis, the forest loss areas detected using our method are found to be similar to the estimations from Global Forest Watch. These results highlight the fact that this method provides not only quick alerts but also reliable detections that can be used to calculate weekly, monthly, or annual forest loss statistics at a national scale.

Highlights

It is interesting to note that the minimum mapping unit (MMU), when reported in the 28 papers, is always larger than 0.2 ha, except in [13,14,15]. We found this surprising given the high impact of the MMU on forest loss detection accuracy
We investigated the adaptation of the forest loss detection method to the context of Vietnam, Laos, and Cambodia
We found that the proportion of forest disturbances occurring in protected areas in relation to the total amount of disturbances in Vietnam in

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The world’s forests have undergone substantial changes in the last few decades. The authors of [1] estimated that 17% of moist forests disappeared between 1990 and 2019. In certain regions and countries, these changes have been more rapid. This is the case in the Greater Mekong subregion, which is recognized as deforestation hotspot

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