It is very hard to keep tabs on logging in Indonesian rainforest, and estimates of the rate of forest loss vary wildly. For the current decade (2000 to 2005) the United Nations Food and Agriculture Organization (FAO) estimated a clearance rate of 1.87 million hectares per year, while a pan-humid tropical forest clearing survey came up with a figure of 0.7 million hectares per year for the same period.

Using satellite imagery Matthew Hansen from South Dakota State University, US, and colleagues, have managed to resolve this discrepancy and provide a clearer picture of what is happening on the ground in Indonesia.

Similar techniques have already been applied in Brazil to monitor the Amazon rainforest, but until now hadn't been applied over Indonesia due to problems with excessive amounts of cloud cover blocking the view. However, higher resolution and more frequent imaging is enabling scientists to build up pictures of cloudier countries, such as Indonesia and the Congo Basin in Africa.

Hansen and colleagues gathered satellite images of the whole of the Indonesian archipelago, dating between 1990 and 2005. By bundling the images into two intervals (1990–2000 and 2000–2005) they were able to estimate how logging practices had changed over time. In addition, the more detailed images of recent years provided them with annual resolution of the changes.

The results show a dramatic reduction in clearing from the 1990s (an average of 1.78 million hectares per year) to the current decade (an average of 0.71 million hectares per year between 2000 and 2005). But hidden inside the average for the current decade they found a rapid increase in logging, rising to over 1 million hectares per year by 2005.

Much of this pattern can be explained by political, social, economic and climatic influences. Strong economic growth during the 1990s led to a major expansion of oil palm estates, providing palm oil for international export. On top of this the 1997/1998 El Niño Southern Oscillation (ENSO) event led to prolonged drought and widespread human-induced forest fires.

But by the late 90s the tide had turned, with an economic crisis and a change in government bringing stricter policies and regulations on palm oil plantations. "We posit that unique circumstances at the end of the 90s led to a brief slowing in clearing," Hansen told environmentalresearchweb.

However, annual estimates of forest clearance between 2000 and 2005 indicate that this reduction in forest clearance appears to have been short lived. By 2005 clearance levels had reached 1.17 million hectares per year, possibly related to a recovering Indonesian economy and increased commodity prices.

Although depressing, these clear and reliable satellite estimates may help to bring about change. "Remote sensing can provide critical facts on what is going on in the forest and it brings transparency to the issue," said Hansen. "All parties, whether government, private industry, or civil society may use this information to better manage forest resources."

The researchers reported their work in Environmental Research Letters.