Because of the high altitude and harsh climate, there are few insects in Tibet. Snow leopards are hunted for their fur and the eggs of black-necked cranes have been collected as a delicacy food. Economy The Tibetan economy is dominated by subsistence agriculture. Due to limited arable land, the primary occupation of the Tibetan Plateau is raising livestock, such as sheep, cattle, goats, camels, yaks, dzo, and horses. The main crops grown are barley, wheat, buckwheat, rye, potatoes, and assorted fruits and vegetables. Tibet is ranked the lowest among China's 31 provinces on the Human Development Index according to UN Development Programme data. In recent years, due to increased interest in Tibetan Buddhism, tourism has become an increasingly important sector, and is actively promoted by the authorities. Tourism brings in the most income from the sale of handicrafts. These include Tibetan hats, jewelry (silver and gold), wooden items, clothing, quilts, fabrics, Tibetan rugs and carpets. The Central People's Government exempts Tibet from all taxation and provides 90% of Tibet's government expenditures. However most of this investment goes to pay migrant workers who do not settle in Tibet and send much of their income home to other provinces. Forty percent of the rural cash income in the Tibet Autonomous Region is derived from the harvesting of the fungus Ophiocordyceps sinensis (formerly Cordyceps sinensis); contributing at least 1.8 billion yuan, (US$225 million) to the region's GDP. The Qingzang railway linking the Tibet Autonomous Region to Qinghai Province was opened in 2006, but it was controversial. In January 2007, the Chinese government issued a report outlining the discovery of a large mineral deposit under the Tibetan Plateau. The deposit has an estimated value of $128 billion and may double Chinese reserves of zinc, copper, and lead. The Chinese government sees this as a way to alleviate the nation's dependence on foreign mineral imports for its growing economy. However, critics worry that mining these vast resources will harm Tibet's fragile ecosystem and undermine Tibetan culture. On January 15, 2009, China announced the construction of Tibet's first expressway, the Lhasa Airport Expressway, a stretch of controlled-access highway in southwestern Lhasa. The project will cost 1.55 billion yuan (US$227 million). From January 18–20, 2010, a national conference on Tibet and areas inhabited by Tibetans in Sichuan, Yunnan, Gansu and Qinghai was held in China and a plan to improve development of the areas was announced. The