BEIJING, June 6 -- The vast barren deserts which cover almost a quarter of the earth's land may not be as lifeless as many people think.

    A UN report issued yesterday reveals that rather than the traditional image of empty parched earth, deserts are actually complex eco-systems teeming with life, while the marginal areas at their edges are home to 500 million people.

    But like the rest of the earth's delicate environment deserts also face problems the report warns that climate change coupled with growing populations pose a significant threat to these delicate areas.

    Coinciding with yesterday's World Environment Day the theme of which was "don't desert drylands" this year the United Nations Environment Programme (UNEP) debuted its "Global Deserts Outlook" report.

    As well as detailing the historic origins and astonishing biodiversity of the world's deserts, the report includes a possible vision for the future of deserts and the challenges of managing them.

    It forecasts that deserts will confront growing pressures in coming decades.

    Global climate change, coupled with increasing population pressure, particularly at their edges, is likely to affect the more productive desert areas and pose new and significant threats to biodiversity and sensitive species, it warns.

    "One might think of deserts as 'barren' or 'death-like', but we have to change our minds a little after reading this," said Shao Xuemin, representative of the UNEP Office in Beijing.

    "Deserts are not just the barren wastelands they are generally seen as," he said, "they are home to millions of people and have rich biodiversity."

    And deserts are important corridors for migratory species like birds and insects, as well as for trade and cultural exchanges, according to the report.

    Deserts present serious challenges for sustainable development, but also great opportunities, it adds.

    Irrigated areas of desert in China, India and Pakistan are facing declining crop yields due to increasing salinity.

    And in China deterioration of the plant cover in the headwater regions of the Yangtze River has created major flooding problems downstream, as well as massive erosion in the Loess Plateau.

    But deserts, which receive more energy from the sun than any other part of the earth's surface, also have a huge potential to produce renewable power.

    So far only a tiny fraction of their solar power potential has been harnessed but, with a decline in the production of fossil fuel, desert-based solar sources could supply a significant portion of global energy by 2050, said the report.

    Desert currently covers 2.64 million square kilometres of China, roughly 27 per cent of the country's total landmass.