Forested areas in Europe, North America, the Caucasus and Central Asia have been increasing steadily, growing by 25 million hectares over the past two decades, the United Nations said Monday, citing diseases, insects and storms aggravated by climatic factors as the major threats to the ongoing health of woodlands.

"In addition to forest area, the volume of wood in pan-European forests is growing by over 430 million cubic metres every year due to the expansion of the forest area and increases in stock levels," the UN Economic Commission for Europe (UNECE) said on World Forest Day, as experts gathered in Geneva to review trends in forests and forest resources in Europe and North America.

In total, the UNECE region has 40 per cent of the world's forests, most of them classified as boreal or temperate.

Forests play an important role in the conservation of biological diversity and the area of forest primarily designated for this purpose is also expanding, according to UNECE. In the UNECE region it increased by almost 25 million hectares – an area slightly larger than the United Kingdom – between 1990 and 2010, and currently accounts for about 8 per cent of the total forest area in the region.

Most of this increase took place in Europe, the Caucasus and Central Asia, where the area of forest specifically managed for conservation of biological diversity has been increasing by almost one million hectares annually over the past 20 years, while in North America it has increased by more than 5 million hectares since 1990.

Increasing climate variability, however, has had a negative impact on forest growth and health, with North America reporting the largest area of forests with insect-related health problems in 2005 compared to any other region.

Problems include outbreaks of the mountain pine beetle, which has devastated more than 11 million hectares of forest in Canada and the western United States since the late 1990s – an unprecedented outbreak aggravated by higher winter temperatures. During the same period damage resulting from storms, wind and snow affected 0.4 per cent of the forest area.

Meanwhile, 19 forest policies from 16 countries have been nominated to contend for the International Policy Award for Visionary Forest Policies, sponsored by the World Future Council, an international policy research organization that provides decision makers with effective policy solutions.

Three winning policies will be announced on 21 September at UN Headquarters, according to the UN Convention on Biological Diversity, the International Year of Forests 2011 and the UN Forum on Forests.