WAGENINGEN, The Netherlands - Current rates of tapping frankincense are endangering the fragrant resin's sustained production, ecologists from the Netherlands and Eritrea warned today.
Frankincense is an aromatic hardened wood resin obtained by tapping Boswellia trees. For 2000 years, the resin has been important as an ingredient in incense and perfumes, especially popular in Christian communities at Christmas. But ecologists say frankincense production in the Horn of Africa is declining because Boswellia woodlands are failing to regenerate.
Writing in the December issue of "Journal of Applied Ecology," the ecologists said that overtapping the trees results in them producing fewer, less viable seeds.
According to the Bible, frankincense was given to the baby Jesus by the three wise men at Christmas. As a result the resin is especially in demand for modern Christmas celebrations, and it will be featured in thousands of Nativity plays.
In many Arab communities today, festive events like weddings, Eid celebrations, and the birth of a newborn are incomplete without the burning of frankincense. In Omani homes across the sultanate, frankincense is indispensable to the ritual of demonstrating one's hospitality to visiting guests.
To determine why the Boswellia trees are failing to regenerate, the ecologists hypothesized that intensive tapping is causing the trees to divert too much carbohydrate into resin, at the expense of reproductive organs, such as flowers, fruit and seeds.
Working in southwestern Eritrea, they tested the hypothesis by looking at how many seeds intensively tapped trees produced, and their germination rates, compared with untapped trees.
Although the impact of tapping trees for other crops, such as latex and pine resin, has been studied in plantations, this is the first study to show quantitatively the fragile relationship between the extraction of resins and tree regeneration in natural populations.
Study co-author Professor Frans Bongers of Wageningen University said, "This study strongly suggests that there is competition between investment of carbohydrates in sexual reproductive structures and synthesis of frankincense in Boswellia papyrifera." 
Boswellia papyrifera is one of five species of Boswellia used in the making of frankincense.
"At all study sites, trees subject to experimental tapping produced fewer flowers, fruits and seeds than trees that were exempt from tapping," said Bongers, an expert in tropical forest ecology.
"Furthermore," he said, "tapped trees produced smaller fruits with seeds of lower weight and reduced vitality than non-tapped trees."
To obtain the frankincense, a deep, longitudinal incision is made in the trunk of the Boswellia tree and below it a narrow strip of bark is peeled off. When the milky juice which exudes has hardened by exposure to the air, the incision is deepened. In about three months the resin hardens into large clear yellow globules which are scraped off into baskets.
Based on their findings, the authors say that for production to be sustainable, the way that frankincense is tapped needs to be changed.
"In order to control the decline in fruit and seed production, less intensive tapping procedures should be developed," they write.
The study found that six tapping points per tree are already having a negative impact, so the authors suggest reducing the number of tapping points.
They say new tapping regimes should include rest periods when there is no resin harvesting to allow the trees to recover.
At least five species of Boswellia are currently exploited for frankincense. In addition to those in Eritrea, Boswellia woodlands are found in Nigeria, Chad, Sudan, Kenya, Tanzania, Somalia, Yemen and Oman.
Boswellia papyrifera is a small deciduous tree that grows in a savanna belt stretching from northern Nigeria eastwards to the highlands of Eritrea and Ethiopia.
In Eritrea, it grows under semi-arid conditions in shallow soils on rocky slopes. Despite its economic importance, B. papyrifera is a threatened species in Eritrea where Boswellia woodlands are being destroyed for agricultural land.