Aug 24, 2012
Mapping tropical forest loss in Sumatra
Indonesia has the second highest deforestation rate for a tropical country. Using a new assessment approach, researchers have found that from 1990 to 2010 Sumatra lost 7.54 million hectares of primary forest and saw a further 2.31 million hectares degraded. The bulk of the cleared forest – 7.25 million hectares – had already been degraded.
"The methods are straightforward and repeatable," Belinda Arunarwati Margono of South Dakota State University, US and The Ministry of Forestry of Indonesia told environmentalresearchweb. "Indonesia is applying a moratorium of logging from 2011–2013; the results are a valid baseline for monitoring the effectiveness of the moratorium."
Margono and colleagues used a hybrid approach to analyse forest changes, employing a per-pixel supervised classification mapping of LandSat images and Geographical Information System (GIS)-based fragmentation analysis.
"We really wanted to provide a means to assess the second D in REDD [Reducing Emissions from Deforestation and Forest Degradation]," said Margono. "The hybrid approach allows us to do this."
Margono explained that per-pixel mapping is used successfully for mapping forest extent and stand-replacement disturbance, but is not easily applicable for mapping degradation in Indonesia. "Indonesia is very cloudy and you often do not 'see' the logging event, which does not persist as vegetation recovery quickly obscures the site of disturbance," she said. "So we need a different method for mapping degradation in Indonesia."
With that in mind the team used GIS-based fragmentation analysis to map all human-observable landscape features that persist, such as roads and villages. "We assume primary-forest degradation to exist in proximity to these features and intact primary forests to be removed from these features," said Margono.
The team also used LIDAR data from the Geoscience Laser Altimeter System (GLAS) onboard IceSat-1 to "verify that our hybrid methodology did in fact map primary forests of different structure". The LIDAR indicated that primary-intact forest had a mean tree canopy height of 28 m whereas primary-degraded forests were on average just 19 m high.
"The two approaches are applicable at the global scale, yet handy and easy to repeat at national scales," said Margono.
The researchers found that the intact primary forests of Sumatra have lost 40% of their area, while the degraded primary forests have lost 33%. The rate of primary-forest cover loss and primary-forest degradation slowed over the 20 years under study – from 7.34 million hectares between 1990 and 2000, to 2.51 millionhectares over the following 10 years. But this slowdown may be because much of the lowland primary forest has already disappeared.
Large-scale commercial logging and agro-industrial development are the main drivers of Sumatran forest loss, wrote the researchers in Environmental Research Letters (ERL). Global markets for pulp, timber and oil palm are expanding and, according to some estimates, illegal logging makes up more than half of total domestic timber production.
"It is obvious that there is a strong need to have a robust method for distinguishing intact from degraded forms of primary forest," said Margono. "The impact on carbon stocks and other ecosystem services by selective logging is important to quantify, but first needs to be identified in an explicitly spatial way. Results of this study are valuable for sustainably managing Sumatra's forests, and useful for depicting a Reducing Emissions from Deforestation and Forest Degradation (REDD and REDD+) baseline."
The researchers will use Sumatra as a model for further analysis elsewhere in Indonesia. "We will work on mapping primary-forest cover loss and degradation for the whole of the country and examine how much of it is occurring within different landforms – wetlands, uplands and montane settings," said Margono. "We believe this will be a valuable reference for policy formulation in balancing protection and exploitation of Indonesia's forest resources."
About the author
Liz Kalaugher is editor of environmentalresearchweb.