By Richard Black
Environment correspondent, BBC News website, Barcelona
Orangutans are among Sumatra's rich variety of species
Indonesian authorities have pledged to stop the loss of forests and species in Sumatra, one of the world's most ecologically important islands.
Representatives of the island's 10 provinces, national government and the environment group WWF launched the deal at the World Conservation Congress.
Sumatra has lost about half of its forest cover in the last 20 years.
It is home to a number of important and iconic species such as the tiger, orangutan, rhinoceros and elephant.
The island has suffered floods and forest fires in recent years that have been widely attributed to illegal forest clearance.
Two years ago, President Susilo Bambang Yudhoyono was forced to apologise to Singapore and Malaysia when smog from burning Sumatran forest covered the neighbouring countries.
The need to deal with these issues appears to have played a big part in persuading the authorities to act.
"In the rainy months, we are seeing landslides and flooding more often, and it is time to make a real change," said Indonesia's deputy environment minister Hermien Roosita at a news briefing here.
"Every governor from the 10 provinces and four (national) ministries have signed this monumental commitment to ecosystem restoration of the island and protecting the remaining natural forest."
More than 13% of the island's forests lie on peat, which contain vast amounts of carbon that would be lost to the atmosphere if the trees were removed, accelerating climate change.
"When you look at the flora and fauna in this area and the rate of loss that's going on, this is a substantial commitment to protect and restore forests," said Gordon Shepherd, WWF's director of global policy.
The government has already regulated to stop clearance of virgin forest for palm oil plantations - grown for food, industry and biofuels - but the government acknowledges the ban may not be completely effective
As well as protecting and restoring forest, the authorities have pledged to make development on Sumatra obey principles of "ecosystem-based planning", where any projects detrimental to the island's ecological health would be banned.
Indonesian authorities have pledged to stop the loss of species
However, the vice-governor of the province of West Sumatra, Marlis Rahman, said help from the west would be needed to help meet the commitments.
"We are calling on the international community to support us in implementing this commitment on the ground and help us to find extra livelihoods by protecting our forests," he said.
Mr Rahman did not put a figure on how much money might be needed, although he said say technical help was also part of the equation.
With this agreement, Sumatra appears to have put itself in a good position to gain from measures to reduce deforestation as a way of combating climate change.
Such measures are highly likely to become a formal part of any future international agreement on climate going beyond the Kyoto Protocol.