Globally, some 32 million acres of forests were converted to other uses, including agriculture, or were lost through natural causes each year from 2000 to 2010, according to the findings of the U.N. Food and Agriculture Organization report.
The FAO's Global Forest Resources Assessment 2010 says the rate of forest loss has declined from around 40 million acres per year in the 1990s.
More than a third of all forests are classified as primary, defined as showing no visible signs of human intervention.
Primary forests account for 36 percent, or 3.5 billion acres, of the world's forest area but their area has decreased by more than 98 million acres -- at a rate of 0.4 percent annually -- in the past 10 years.
South America accounted for the largest proportion of the loss in primary forests, followed by Africa and Asia.
Legally established protected areas, such as national parks, game reserves and wilderness areas, now cover more than 10 percent of the total forest area in most countries and regions, the report said.
"The world's forests represent a vital source of forest biological diversity. This biodiversity is an important treasure, especially as forests will not just have to adapt to climate change but are also expected to help mitigate it," FAO Assistant Director General Eduardo Rojas said.
"Greater investments in sustainable forest management are urgently required to better conserve and manage forest biodiversity," he said.