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 not reproducing 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 UN Environmental Program have found the number of trees is dwindling in Ethiopia, Eritrea, and Somalia -- which together 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 percent, the report said. Heavily tapped groves produced one-third as many seeds and their germination rate was less than 16 percent.
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" of an area where it is notoriously hard to get good data.
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.
In biblical times, Southern Arabian kingdoms such as Sheba, the Yemen of today, had a monopoly on the frankincense trade and the substance was worth its weight in gold.
Frankincense and myrrh came by ship north through the Red Sea and Persian Gulf, or by camel through the Arabian desert.
Today, top-quality frankincense sells for about $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 ( what is now Turkey), bearing myrrh, another sap incense used in death rites, presaging the Crucifixion.
The Gospel of Matthew doesn't say there were three of the wise men or how long it took between Jesus' birth and their arrival, saying they came from the east following a star that eventually led them to Bethlehem.
Matthew 2:11 says: "When they saw the star, they rejoiced with exceeding great joy. And when . . . they saw the young child with Mary his mother, they fell down, and worshiped him: and when they had opened their treasures, they presented unto him gifts; gold, and frankincense and myrrh."