It turns out that one of the gifts of the three wise men to the baby Jesus, frankincense, would be much for valuable today because the trees from which it comes are disappearing. Frankincense is produced by the Boswellia tree and it's collected as a resin, which oozes from cuts made in the bark like latex from rubber. The tree probably produces the resin to ward off grazing animals and attacks from fungi, but it doesn't deter humans. Indeed, in Eritrea, which exports frankincense and where it's also used medicinally and culturally, workers make incisions in the trees after the monsoon and collect the resin every three weeks or so. But could chemically robbing the trees every year in this way have an impact on their health? To find out Toon Rijkers and his colleagues compared the germination of seeds from tapped and untapped trees. Only 20% of the seeds from tapped trees grew, compared with over 90% of seeds from their untapped counterparts. Taking the resin seems to place a serious drain on the trees' chemical condition, suggest the researchers, who found that tapped trees also produced fewer flowers, fruits and seeds. The consequence, they say, has been a severe reduction in the natural regeneration of Eritrean Boswellia trees. The solution, they say, may be to remove less resin and also give selected trees a "year off" now and then.