Eduardo Rojas, assistant director of the FAO's forestry department, said: "For the first time, we are able to show that the rate of deforestation has decreased globally as a result of concerted efforts taken both at local and international level."
The FAO, based in Rome, said tougher legislation had helped curb destruction of woodland.
Seventy-six countries have issued or updated forest policies since 2000, many of them allocating woodland to local communities for sustainable development.
The proportion of forests contained in national parks and other legally-protected areas has climbed to 13 per cent, having risen by 94 million hectares since 1990.
Forests cover just over four billion hectares or 31 per cent of the world's total land area.
They store about 289 gigatonnes of carbon, more than all the carbon in the atmosphere, but this decreased by 0.5 gigatonnes a year during 2000 to 2010.
"A lower deforestation rate and the establishment of new forests have helped bring down the high level of carbon emissions from forests caused by deforestation," Mette Loyche Wilkie, co-ordinator of the FAO's 2010 global forest resources assessment, said.
However, Wilkie warned tree planting programmes in China, India and Vietnam, accounting for most of the recent gains in forest area, would end by 2020.
Urging governments to quickly put in place measures to slow deforestation, Wilkie said: "Without such interventions, we risk a sudden return to high rates of net forest loss and of carbon emissions from forests, which we had in the 1990s."
Indonesia sharply reduced the speed of its deforestation to 0.5 million hectares a year between 2000 and 2010, against 1.9 million a year during the previous decade.
Brazil lowered its own figure to 2.6 million from 2.9 million hectares.
South America, nonetheless, still had the highest regional level of net deforestation at 4 million hectares a year, followed by Africa with 3.4 million hectares.
In North and Central America, the forest area remained fairly stable, while in Europe it continued to expand, although at a slower rate than previously.