Researchers from the US have used remote-sensing data to put together the first-ever annual maps showing forest-cover loss on the islands of Sumatera (also known as Sumatra) and Kalimantan, Indonesia.

Mapping Indonesia from space is hugely challenging because of persistent cloud cover. But Mark Broich and his colleagues from South Dakota State University and the World Resources Institute, both in the US, developed algorithms to analyse the history of each pixel in nine years' worth of satellite images (2000–2008).

"Indonesia is second only to Brazil in terms of area of humid tropical forest-cover loss," Broich told environmentalresearchweb. "But analysing data from Brazil is simpler because a dry season allows cloud-free satellite images to be taken every year."

Until now, estimates of forest-cover loss for Indonesia were based on multi-year averages, but the maps produced by Broich and his team revealed some interesting annual events.

"We found a very high fluctuation rate from one year to another, which makes it challenging to develop a baseline for the REDD+ policy framework," said Broich. These high fluctuations in forest-cover loss are, Broich believes, in part due to the harvesting of timber plantations. "Our results do not yet differentiate between the type of forest that has been cleared," he said. "In Brazil forest is cleared for agriculture. But in Indonesia tree plantations are established and then harvested."

So while his analysis showed that the total forest-cover loss for Sumatera and Kalimantan for 2000–2008 was 5.39 Mha (9.2% of the year 2000 forest cover of these two islands), Broich believes that 50% of this forest cover loss could be attributed to harvesting of tree plantations.

The annual analysis also showed that the trends for Sumatera and Kalimantan were distinctly different, driven primarily by the trends of Riau and Central Kalimantan provinces, respectively.

"This analysis shows that annual mapping of forest-cover change yields a clearer picture than a one-time overall national estimate," said Broich.

The researchers published their research in Environmental Research Letters (ERL).