IF ONLY, Chinese leaders might be thinking, Tibetan medicine had the power to pacify. In recent years rural incomes in eastern areas of the vast Tibetan plateau have been soaring, thanks to a surge in Chinese demand for Tibetan herbal remedies. But in late January the same region experienced the biggest outbreak of violent unrest since a surge of Tibetan discontent across the plateau in 2008. Police have shot dead several demonstrators. There is every sign the unrest could spread.

The shootings follow on from the self-immolation of 16 Tibetans, including monks and nuns, over the past year, some of them fatal. Now security across Tibet and Tibetan-inhabited areas of neighbouring provinces has been tightened in an effort to stop protests—including self-immolations—from spreading. The violence has so far been limited to Tibetan-dominated areas of Sichuan province, to the east of Tibet proper (see map). But the recent shootings of unarmed demonstrators are bound to arouse powerful emotions elsewhere on the Tibetan plateau.

Police have sealed off affected areas to prevent access by foreign journalists, making reports of recent events difficult to confirm. But Western human-rights organisations say protests broke out in several villages and rural towns in Sichuan from mid-January onwards, and that police opened fire on three or four occasions, killing several people. In the most recent incident, on January 26th, a crowd of Tibetans attempted to block the way of police who had arrested a protester in a township in Rangtang county. Police shot into the crowd, reportedly killing one Tibetan.

To Chinese officials, the violence should reaffirm that rising prosperity is far from being the guarantor of stability that many of them suppose. The areas where the immolations and protests occurred are still relatively backward. But in Ganzi, a prefecture that has seen some of the worst unrest, rural incomes rose by an average of 30% in 2011. They are projected to rise just as much again this year.

A big contributor to this has been a voracious appetite in other parts of China for the region's “caterpillar fungus”, a mushroom that grows in the bodies of dead caterpillars on high-altitude grasslands. Claimed to be an aphrodisiac, it can be worth more than its weight in gold. The Sichuan government reported in 2010 that in Aba county, another centre of unrest, most peasants were getting up to nine-tenths of their income from it, at the expense of traditional herding and farming.