The United States and much of Europe have reversed years of deforestation and are showing a net increase in wooded areas, while most developing countries continue to cut down their trees, a U.N. agency said Tuesday.

The Rome-based Food and Agriculture Organization said in its biannual report on the State of the World's Forests that economic prosperity and careful forest management had positive effects.

However, poor or conflict-stricken countries — where clear-cutting and uncontrolled fires are especially severe — still face serious challenges in managing their wooded areas, the agency said.

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"Deforestation continues at an unacceptable rate" of about 32 million acres a year, said Wulf Killmann, a forestry expert at the agency.

However, he noted in a positive sign that the net loss had decreased over the last decade from 22 million acres to 17 million acres.

The United States reported an annual increase in forest area of 0.12 in the 1990s and 0.05 percent from 2000 to 2005.

That increase, however, was accompanied by deforestation in Mexico, which reported a 0.52 percent decrease in the 1990s and a 0.40 percent decrease in wooded areas from 2000 to 2005. Canada reported no change during those periods.

In Europe, the report said the net increase was due to efforts in Spain and Italy, followed by Bulgaria, France, Portugal and Greece.

Africa, Latin America and the Caribbean are currently the regions with the highest losses of wood-covered regions, especially in tropical areas.

Africa, which accounts for about 16 percent of the global forests, lost over 9 percent of its trees between 1990 and 2005, the agency said.

In Latin America and the Caribbean, home to nearly half of the world's forests, 0.5 percent were lost every year between 2000 and 2005 — up from an annual net rate of 0.46 percent in the 1990s.

On the positive side, wooded area increased in Asia between 2000 and 2005.

The increase was limited to East Asia, where investment in tree plantations in China offset high rates of clear-cutting in other regions, the report said.

Forested area in most European countries is also increasing, while it is stable in Canada and the United States.

Among the major causes of deforestation cited by Killmann were conversion of land for farming or livestock.

Forests cover just under 9.88 billion acres, about 30 percent of the world's land area. The world lost 3 percent of its wooded areas between 1995 and 2000, the agency said.