Are soaring goat numbers milking China of its natural resources?

The world's finest cashmere comes from Tibetan and Mongolian goats. To withstand the bitter climate in such countries, cashmere goats not only have a fleece of thick long hairs, but also an undercoat of fine down. This down is combed out each spring, and once unwanted long hairs, grease, dirt and dried faeces are separated out, each goat produces maybe three or four ounces of cashmere. That is enough for between a third and a half of a sweater, whereas a sheep provides three or four sweaters, and that's why cashmere clothing used to be so expensive.

Good cashmere fibres are between 13 and 16.5 microns thin, compared to fine wool from Merino sheep which range in thickness between 24 and 28 microns in diameter.

The number of goats in Mongolia has doubled since 1990 to about 11m, while the number in China's Inner Mongolia has risen from eight million to 19 million.

Thanks to the growing number of goats in China, cashmere sweaters are now as cheap as hell - but thanks to those sweaters, the once green frontier of China's Inner Mongolia looks increasingly like hell as well. Those goats, who have grown in number along with cashmere orders from retailers like Wal-Mart and CostCo, are tearing up grass faster than ever, helping to turn Genghis Khan's grasslands into desert.

Cashmere goats are definitely not grasslands friendly. Unlike yaks, which graze lightly with minimal impact, cashmere goats graze voraciously - consuming all greenery and ripping grass out by the roots. The sharp hooves of cashmere goats can pierce the soil surface (a crust that is composed of fungi, mosses, lichens and bacteria that help retain moisture). Once the crust is torn, strong winds in Mongolia can carry away the sand underneath in dust storms.

Cashmere goats have grazed much of China's grasslands down to nothing, causing severe dust storms and political storms.

The destructive goat is the animal that has most changed the old world and made way for the new. Its methodical mastication of the forests of the Middle East enabled man to create clearings in which to cultivate crops and keep other animals.

Firewood, however, was still needed for cooking fuel and, as the goat demolished all supplies in its immediate vicinity, man was forced to move in its wake.

It was centuries before it occurred to man to replant the trees destroyed by his herds of goats, and this short-sighted policy created the deserts of the Middle East and Sahara, and the ecology of the countries bordering the Mediterranean was drastically altered by the soil erosion that followed the extinction of the flora.

Norman law banned goats from forests. The earliest forest laws in England gave rights to commoners to graze cattle, horses and pigs in the woods at certain seasons of the year, but forbade them to graze sheep and goats, because of the damage they did, and this law is still in force today.

Under 13th-century Scots law, if goats were found in a forest three times the forester hung one from a tree by the horns and, if four times, he killed and disembowelled one on site.

Before the clearances of the 19th century, goats were more numerous than sheep in Scotland. The number each croft could carry was laid down as two or three dozen, but was frequently exceeded.

The crofters kept goats for milk and meat and every part of them was put to good use. Their fat became tallow for candles, their skins knapsacks and containers, while ropes made from their hair were said not to rot in water. The ropes of goat hair intertwined with pigs' bristle, used by the islanders on St Kilda to suspend themselves from cliff tops in search of gulls' eggs, were heirlooms passed from one generation to the next.

Compared with other categories of livestock there are now very few goats left in Scotland.

Still, we must remember that China has vast numbers of them, and that a low-priced cashmere sweater may well have an unacceptable, hidden environmental cost attached to it.