Environment correspondent, BBC News website
Demand for biofuels will add to pressure on forests, the report warns
Demand for land to grow food, fuel crops and wood is set to outstrip supply, leading to the probable destruction of forests, a report warns.
The Rights and Resources Initiative (RRI) says only half of the extra land needed by 2030 is available without eating into tropical forested areas.
A companion report documents poor progress in reforming land ownership and governance in developing countries.
Both reports were launched on Monday in UK government offices in London.
Supporters of RRI include the UK's Department of International Development (DfID) and its equivalents in Sweden and Switzerland.
The dual crises of fuel and food are attracting significant land speculation
Andy White, RRI
"Arguably, we are on the verge of a last great global land grab," said RRI's Andy White, co-author of the major report, Seeing People through the Trees.
"It will mean more deforestation, more conflict, more carbon emissions, more climate change and less prosperity for everyone."
Rising demand for food, biofuels and wood for paper, building and industry means that 515 million hectares of extra land will be needed for growing crops and trees by 2030, RRI calculates.
But only 200 million hectares will be available without dipping into tropical forests.
The report foresees demand increasing further into the century.
It cites studies suggesting that "...if the current plateau in productivity continues, the amount of additional agricultural land required just to meet the world's projected food demand in 2050 would be about three billion hectares, nearly all of which would be required in developing countries."
According to UN figures, the world currently has about 1.4 billion hectares of arable land and about 3.4 billion hectares of pasture.
Some academics place their hopes in agricultural technologies including genetic engineering to boost crop yields.
But since the spectacular successes of the Green Revolution, advances have been slow. In some areas, yields are falling - a trend which is likely to be exacerbated by climate change.
However, eating into tropical forests to create extra agricultural land would, in turn, exacerbate climate change, with deforestation currently accounting for about 20% of greenhouse gas emissions.
One of RRI's main conclusions is that reform of land ownership is crucial, if large-scale pillage of tropical forests is to be avoided.
The conclusion have been supported by DfID, whose minister Gareth Thomas was one of the speakers at the launch event.
"These new studies should strengthen global resolve to protect the property rights of indigenous and local communities who play a vital role in protecting one the most outstanding natural wonders of the world," he said.
DfID runs programmes in West Africa aimed at helping forest dwellers acquire the legal right to manage their land.
Many indigenous peoples need help in acquiring rights to the land they live on
"It is clear that the dual crises of fuel and food are attracting significant new investments and great land speculation," said Andy White.
"Only by protecting the rights of the people who live in and around the world's most vulnerable forests can we prevent the devastation these forces will wreak on the poor."
But the second RRI report - From Exclusion to Ownership? - says progress in reforming ownership has been slow, with only a few countries such as Brazil, Cameroon and Tanzania handing over significant tracts to local communities.
Moves to curb climate change by preserving forests in developing countries could help, RRI concludes. But it also raises the question of who owns rights to the trees - the rich Western countries that want to fund carbon sequestration, or the people who live in the forest areas?
Sorting out ownership could not only help on the environmental front, but also remove reasons for conflict. RRI calculates that about two-thirds of the world's current violent conflicts are driven by land tenure issues.