ERIGAVO, Somalia — In a tradition dating to Biblical times, men rise at dawn in the rugged Cal Madow mountains of Somaliland in the Horn of Africa to scale rocky outcrops in search of the prized sap of wild frankincense trees.

Bracing against high winds, Musse Ismail Hassan climbs with his feet wrapped in cloth to protect against the sticky resin. With a metal scraper, he chips off bark and the tree's white sap bleeds into the salty air. "My father and grandfather were both doing this job," said Hassan, who like all around here is Muslim. "We heard that it was with Jesus."

When dried and burned, the sap produces a fragrant smoke which perfumes churches and mosques around the world. Frankincense, along with gold and myrrh, was brought by the Three Kings as gifts in the Gospel account of the birth of Jesus.

But now these last intact wild frankincense forests on Earth are under threat as prices have shot up in recent years with the global appetite for essential oils. Overharvesting has led to the trees dying off faster than they can replenish, putting the ancient resin trade at risk.