A 50-m Forest Cover Map in Southeast Asia from ALOS/ PALSAR and Its Application on Forest Fragmentation Assessment

Southeast Asia experienced higher rates of deforestation than other continents in the 1990s and still was a hotspot of forest
change in the 2000s. Biodiversity conservation planning and accurate estimation of forest carbon fluxes and pools need
more accurate information about forest area, spatial distribution and fragmentation. However, the recent forest maps of
Southeast Asia were generated from optical images at spatial resolutions of several hundreds of meters, and they do not
capture well the exceptionally complex and dynamic environments in Southeast Asia. The forest area estimates from those
maps vary substantially, ranging from 1.736106 km2 (GlobCover) to 2.696106 km2 (MCD12Q1) in 2009; and their
uncertainty is constrained by frequent cloud cover and coarse spatial resolution. Recently, cloud-free imagery from the
Phased Array Type L-band Synthetic Aperture Radar (PALSAR) onboard the Advanced Land Observing Satellite (ALOS)
became available. We used the PALSAR 50-m orthorectified mosaic imagery in 2009 to generate a forest cover map of
Southeast Asia at 50-m spatial resolution. The validation, using ground-reference data collected from the Geo-Referenced
Field Photo Library and high-resolution images in Google Earth, showed that our forest map has a reasonably high accuracy
(producer’s accuracy 86% and user’s accuracy 93%). The PALSAR-based forest area estimates in 2009 are significantly
correlated with those from GlobCover and MCD12Q1 at national and subnational scales but differ in some regions at the
pixel scale due to different spatial resolutions, forest definitions, and algorithms. The resultant 50-m forest map was used to
quantify forest fragmentation and it revealed substantial details of forest fragmentation. This new 50-m map of tropical
forests could serve as a baseline map for forest resource inventory, deforestation monitoring, reducing emissions from
deforestation and forest degradation (REDD+) implementation, and biodiversity.