The resin is made from gum produced by the boswellia papyrifera tree and used as incense in religious rituals in many cultures, and as an ingredient in perfume and Chinese traditional medicine.
Dutch and Ethiopian researchers, writing in the Journal of Applied Ecology, say they found as many as 7 percent of the scrub-like trees in northern Ethiopia are dying each year, victims of over-harvesting and insects.
The Ethiopian trees that are the source of much of the world's frankincense are declining so dramatically production could be halved over the next 15 years and the trees themselves could decline by 90 percent in the next 50 years, the researchers said.
Frankincense has been harvested in the Middle East and the Horn of Africa since ancient times and that carried by the three wise men probably came from that area, but those trees are mostly gone, said Frans Bongers, a professor of tropical forest ecology and management at the University of Wageningen in Holland.
"There's still some in Somalia, but no one knows how much. The main production area in the world right now is Ethiopia," Bongers said.