On the Tibetan Plateau, the cash crop is a parasitic fungus

Half a kilogram of dried cordyceps fungi can fetch$50,000 US.

Demand from China alone has created a booming economy that ramps up in the spring whenTibetannomads leave their farms and yak herds to take part in aweeks-long gold rush that flows from thefungalbloom. Canadian photographer Kevin Frayershows howTibetan nomadsbring theprized fungus to market.

The best product comes from high on the Tibetan Plateau.

The mountaingrasslands of Tibet's high country are home to the parasiticophiocordycepssinensis, orcaterpillar fungus, which isa member of thecordycepsgenus known forinvadingthe bodiesof insects before releasing their spores.

The product is amummified caterpillar.

It's not the fungus itself that is prized, buttheremains of itshost:aspecies of caterpillarthat thecordycepsinvadesand killsat itslarvae stage.

Once harvested, the dried caterpillar carcasses are sold intact and made into herbal treatments that purportedly heal ailments ranging from asthma to impotence to cancer.

The annual harvest is a state-sponsored industry.

Tibetan nomads who earn little from farming and herding can bring in enough income during the harvest to last through the year. A proficient picker can collect hundreds of theinfected carcasses a day and the finest specimens fetch a high price at market.

It's an ancient practice.

Records ofcordycepsharvesting, known asYartsagunbu, or simply "bu," in Tibet, go back to the15thcentury, and the primary consumer has always beenChina.

The harvest is a game-changer in Tibet.

Nowadays, the industry has transformed rural Tibetan areas where roughly40 per cent of the local economy comes from the shortharvest.

Environmentalists say the harvest is degrading the grasslands.

Now a state-sponsored industry, over-harvesting of cordycepsmay be to blame fordegradation of themountain grasslands that the nomad's yak and cattle herds use forgrazing.

Below-average rainfall this year is also expected to yieldthe smallest harveston record, with many pickersreporting hauls way lower than expected.