The destruction of the world's forests, mainly to make way for agricultural land, has decreased over the past decade, but continues at an 'alarmingly' high rate in many countries, the UN reported Thursday.

Globally, around 13 million hectares of forests were converted to other uses or lost through natural causes each year between 2000 and 2010, as compared to around 16 million hectares per year during the 1990s.The figures were contained in an assessment conducted by the Rome-based UN Food and Agriculture Organisation (FAO). The study covers 233 countries.

'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,' FAO Forestry Department Assistant Director General, Eduardo Rojas, said.

'However, the rate of deforestation is still very high in many countries and the area of primary forest - forests undisturbed by human activity - continues to decrease, so countries must further strengthen their efforts to better conserve and manage them,' he added.

Brazil and Indonesia, which had the highest loss of forests in the 1990s, have significantly reduced their deforestation rates, according to the FAO.

In addition, 'ambitious' tree planting programmes in countries such as China, India, the US and Vietnam - combined with natural expansion of forests in some regions - have added more than seven million hectares of new forests annually. As a result, the net loss of forest area was reduced to 5.2 million hectares per year between 2000 and 2010, down from 8.3 million hectares annually in the 1990s.The world's total forest area is just over four billion hectares, or 31 percent of the total land area.

South America and Africa had the highest net annual loss of forests in 2000-2010, with four and 3.4 million hectares respectively. Oceania also registered a net loss, due partly to severe drought in Australia since 2000. Asia, on the other hand, registered a net gain of some 2.2 million hectares annually in the last decade, mainly because of large-scale afforestation programmes in China, India and Vietnam, which have expanded their forest area by a total of close to four million hectares annually in the last five years.However, conversion of forested lands to other uses continued at high rates in many countries, FAO warned.

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. FAO stressed how forests play an important part in reducing harmful climate change, by storing a vast amount of carbon. But when a forest is cut down and converted to another use, carbon is released back into the atmosphere, FAO said.

'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 and forest degradation,' the FAO assessment's coordinator, Mette Loyche Wilkie, said.

'But we need to look forward because the large tree planting programmes in China, India and Vietnam, accounting for most of the recent gains in forest area, are scheduled to end by 2020,' she added.

'That means we have a short window of opportunity to put in place effective and permanent measures to significantly reduce the current rates of deforestation and forest degradation. Without such interventions we risk a sudden return to the high rates of net forest loss and of carbon emissions from forests, which we had in the 1990s,' she said.

FAO's Global Forest Resources Assessments are published every five years. More than 900 specialists from 178 countries were involved in the Global Forest Resources Assessment 2010. The full report of this Assessment will be released in October 2010.