By Julian Siddle
Science reporter, BBC News
Forests are cleared by burning, which increases carbon emissions
A major international study says palm oil plantations reduce plant and animal diversity, and do little to reduce carbon emissions.
Researchers say tropical forests are increasingly cleared to make way for palm oil crops, leading to a reduction in habitats for many rare species.
The problem is most acute in Malaysia and Indonesia which produce around 85% of the world's palm oil.
The report is published in the journal Conservation Biology.
Palm oil is a common vegetable oil, and is now regarded as a major source of biodiesel, however the researchers question whether it really offers environmental benefits over conventional fossil fuels.
Clearing land to start plantations involves burning huge tracts of forest, a process which produces large amounts of greenhouse gasses such as carbon dioxide.
The researchers estimate at least 75 years of biofuel production is needed from the plantations, to save on emissions anything like the amount of carbon dioxide produced by this burning.
The lead author of the study is Finn Danielsen of Denmark's Nordic Agency for Development and Ecology.
"Our analysis found that it would take 75 to 93 years to see any benefits to the climate from biofuel plantations on converted tropical forestlands," he said.
For the study, Emily Fitzherbert from the Zoological Society of London (ZSL), assessed the impact of palm oil plantations on animal and plant life in Indonesia.
"Anywhere suitable for oil palm plantations throughout the tropics is vulnerable," she said.
"There are loads of different figures and calculations out there on biofuels and the carbon balance, we say these figures are not precise, but the proportions are what's important, to represent the magnitude - oil palm as a biofuel is not a green option," she added.
Sumatran tigers were not found in the plantations
The conversion of tropical forest to plantation also dramatically changed the balance of plants and animals living in the area, overall there was a reduction in plant and animal species says the report.
Some common species increased in number in and around the plantations, wild pigs and leopard cats became dominant, but rarer creatures such as the Sumatran tiger were not seen at all.
"For fauna, only one in six forest species can survive in plantations, the study finds. Plantations are frequently dominated by a few abundant species that are widespread and of low conservation concern," said Matthew Struebig of Queen Mary, University of London, UK.
As well as raising concerns about the loss of biodiversity in plantations, the researchers question the logic of destroying forests to produce biofuels for export to industrialised world markets.
"Subsidies to purchase tropical biofuels are given by countries in Europe and North America supposedly to reduce their greenhouse gas emissions from transport," said Finn Danielsen.
"While these countries strive to meet their obligations under one international agreement, the Kyoto Protocol, they encourage others to increase their emissions as well as breach their obligations under another agreement, the convention on biological diversity.
Fewer animals are found in the plantations compared with the forests
"This is not only an issue in South-East Asia - in Latin America forests are being cleared for soy production which is even less efficient at biofuel production compared to oil palm," added co-author Faizal Parish of the Global Environment Centre in Malaysia.
"Reducing deforestation is a much more effective way for countries to reduce climate change while also meeting their obligations to protect biodiversity."
On a positive note, the researchers found that grassed areas where forest had been destroyed in the past, the land farmed and then abandoned, did become a net absorber of carbon after 10 years of being planted with palm oil.
"Grasslands where you get the earliest payback are scrubby grasslands not natural or unique habitats - but areas that have clearly been trashed," said Emily Fitzherbert.
"Globally we don't want grasslands turned into palm oil plantations. Expansion is going to happen, saying no more palm oil is naive, expand where it will do the least damage and you may get a payback in terms of climate."