AMSTERDAM — A word to the wise men: The world may have plenty of gold and myrrh, but it could run short of frankincense.
Trees in the Horn of Africa provide most of the world's supply of the prized incense that was carried to the infant Jesus by the wise men from the East, in the New Testament's Nativity story. But researchers say the trees are failing to reproduce because they are overexploited for the sap that yields the Christmas staple.
According to a study co-authored by botanists and ecologists from the Netherlands and Eritrea and published this month in the Journal of Applied Ecology, the more heavily a frankincense tree is tapped, the less likely it is to produce viable seeds.
That's not a big problem as long as new trees take root, but other recent studies by scientists and observers from the U.N. Environmental Program have found the number of trees is dwindling in Ethiopia, Eritrea and Somalia -- which make up the bulk of the export market.
They say humans are clearing trees for farmland and allowing their goats to feed on sapling leaves.
The new study found that remaining plants cannot reproduce because they are tapped too heavily and too often.
"At the moment there's not a shortage of frankincense, but there's no regeneration of the forests. There are no young trees anymore," said Frans Bongers, the study's lead author.
In clusters of trees untapped for at least four years, seeds germinated at a rate above 80%, the report said. Heavily tapped groves produced one-third as many seeds and their germination rate was less than 16%.
Eugene Bozniak, chairman of the botany department at Weber State University in Utah, who was not involved in the research, called it a "good solid study" in an area where it is notoriously hard to get reliable data.
Frankincense trees "grow in arid climates. So when you create a wound, which is what you do to make the sap run, they have to devote resources to plugging the wound," he said.
Frankincense is dried sap harvested from several related species of trees found on high scrublands at the southern end of the Arabian peninsula and the Horn of Africa.
Top-quality frankincense sells for roughly $100 a pound in the West, though lower quality can be bought for a tenth of the price.
It's still used in perfumes and herbal medicines, especially in China, and in incense mixes used by various religious groups -- notably the Catholic and Eastern Orthodox churches -- because of the fragrant, citrus-like odor it emits when burned.
The World Conservation Union's "red list" includes 10 species or subspecies of the Boswellia genus -- frankincense -- as "vulnerable" to becoming extinct in the wild.
In western Christianity, tradition holds that the wise men were three kings on camels: Melchior of Arabia, bringing gold to represent Jesus' royal nature; Balthasar from Ethiopia, bringing frankincense, representing his divinity; and Caspar from Tarsus (modern Turkey), bearing myrrh, another sap incense once used in death rites, presaging the crucifixion.
The Gospel of Matthew doesn't say there were three of them, but says they came from the east following a star that led them to Bethlehem.