NANJING, China — Environmentalists worried about the fate of Africa’s dwindling elephant population cheered when China announced a ban on the sale of commercial ivory last year, but an increasingly popular substitute is raising concerns of its own.

To sustain a carving and collecting tradition that is centuries old, many Chinese artisans have turned not to ivory from elephants but from the tusks of extinct mammoths harvested from an unlikely place: the melting permafrost of Russia’s Arctic.

While mammoth ivory has been promoted as an ethical alternative, since it does not come from the poaching of live animals, some conservationists argue that the booming trade in it fuels demand for ivory in general. And the mammoth ivory industry, they say, could end up providing legal cover for the black-market trade in elephant ivory.

The legal importation of mammoth ivory, which comes from creatures that vanished more than 3,600 years ago, has skyrocketed in China as dealers and carvers seek a substitute to meet the demand. In the first six months of this year, more than 27 tons of the ivory entered Heilongjiang, the province that borders Russia’s Far East, the government there announced recently. In the same period last year, it was less than four tons. More mammoth ivory funnels in through Hong Kong, where imports are now averaging 34 tons a year, three times the average in 2003, according to one estimate.