INCENSE for churches around the world could become increasingly scarce, owing to a collapse in the number of trees that produce the sweet-smelling substance.

An article in the journal Nature Sustainability reports that the numbers of Boswellia — the family of trees from which frankincense is extracted — are falling dramatically.

Most forests are no longer able to regenerate themselves naturally, and, in 20 years, projected frankincense production could have halved, the article concludes.

Resin tapped from Boswellia trees hardens into frankincense, which is the base ingredient for most incense burned in churches.

Most of the forests are found in the Horn of Africa, the Arabian peninsula, and India, where cattle grazing, increasing human settlement, over-tapping, and conversion of woodland to pasture are threatening the trees.

The Anglican Benedictine Community at Mucknell Abbey, in Worcestershire, who have been producing incense using traditional recipes for years, was able to source only smaller and poorer-quality frankincense last year.

One of the nuns, Sister Sally, told the Anglican Communion News Service that, while they had enough for now, she was unable to put in another order until the global supply recovered. “If we couldn’t get the frankincense, it would be like trying to make a cake without flour. After all, incense is frankincense.”

Frankincense is collected by slashing the bark of Boswellia trees and then allowing the sticky resin which oozes out to harden before removing it.

This is then mixed with other ingredients, such as myrrh and other aromatic oils, to create the incense that is burned during services.

A report in 2011 by Horticulture Reviews suggested that Britain imported about 30 tonnes of frankincense each year: a small portion of the 1000 tonnes produced annually around the world.

Although the future looks bleak for Boswellia, the researchers in Nature Sustainability report that tree populations could be stabilised. Establishing cattle enclosures and fire-breaks, planting more trees, and tapping existing ones less should allow the forests to begin to replenish themselves and protect the long-term supply of frankincense.

“Concerted conservation and restoration efforts are urgently needed to secure the long-term availability of this iconic product,” the study’s authors conclude.