Abstract
Abstract. The study assesses the extent and trends of forest cover in Southeast Asia for the periods 1990–2000 and 2000–2010 and provides an overview on the main causes of forest cover change. A systematic sample of 418 sites (10 km × 10 km size) located at the one-degree geographical confluence points and covered with satellite imagery of 30 m resolution is used for the assessment. Techniques of image segmentation and automated classification are combined with visual satellite image interpretation and quality control, involving forestry experts from Southeast Asian countries. The accuracy of our results is assessed through an independent consistency assessment, performed from a subsample of 1572 mapping units and resulting in an overall agreement of >85% for the general differentiation of forest cover versus non-forest cover. The total forest cover of Southeast Asia is estimated at 268 Mha in 1990, dropping to 236 Mha in 2010, with annual change rates of 1.75 Mha (∼0.67%) and 1.45 Mha (∼0.59%) for the periods 1990–2000 and 2000–2010, respectively. The vast majority of forest cover loss (∼2 / 3 for 2000–2010) occurred in insular Southeast Asia. Complementing our quantitative results by indicative information on patterns and on processes of forest change, obtained from the screening of satellite imagery and through expert consultation, respectively, confirms the conversion of forest to cash crops plantations (including oil palm) as the main cause of forest loss in Southeast Asia. Logging and the replacement of natural forests by forest plantations are two further important change processes in the region.
Highlights
About 15 % of the world’s tropical forests are located in Southeast Asia (FAO, 1995), including for this study Papua New Guinea (PNG) and the Solomon Islands as part of the Southeast Asia region (Fig. 1)
Stratified sampling might have offered higher efficiency for a single assessment, the choice for a systematic sampling grid has been made to allow for easy, strata-independent follow-up assessments and for direct nesting to national forest inventories, which are in most tropical countries based on systematic sampling designs (Mayaux et al, 2005; Food and Agriculture Organisation (FAO) and JRC, 2012)
Our study focused on the assessment of forest and other woody vegetation cover, on the land cover classes “Tree Cover” (TC), “Tree Cover Mosaic” (TCM) and “Other Wooded Land” (OWL) (Fig. 2)
Summary
About 15 % of the world’s tropical forests are located in Southeast Asia (FAO, 1995), including for this study Papua New Guinea (PNG) and the Solomon Islands as part of the Southeast Asia region (Fig. 1). Forests in continental Southeast Asia consist for the most part of mixed deciduous forest types, including for instance the precious Teak forests, whilst the insular sub-region holds for example large extents of highly productive evergreen Dipterocarpus forests. Southeast Asia’s tropical forests play an important role for environmental protection and biodiversity, as well as for socio-economy and the living conditions of forest-dependent populations (e.g. Lee, 2009). These forests are of importance in the context of global carbon balance. The United Nations Food and Agriculture Organisation (FAO) reported a net annual forest area loss in Southeast Asia of 2.4 Mha in the 1990s, and of 0.4 Mha and 1.0 Mha for the periods 2000–2005 and 2005–2010, respectively (FAO, 2010)
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