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Boswellia papyrifera Hochst. is the most important global source of frankincense. Tree numbers are rapidly decreasing in many populations of B. papyrifera in Ethiopia, where most of the internationally traded frankincense comes from. Improper tapping is among the frequently mentioned reasons for this decrease within populations. We still lack sustainable techniques for frankincense tapping, and these techniques are not yet tuned to individual trees since we are unaware how tree characteristics influence frankincense yield. This study investigates the relationships between different tree characteristics and their relation to frankincense yield. We selected 53 trees and measured frankincense yield and their DBH, tree age, number of leaf apices, radial growth, bark thickness, total resin-canal area, and total number of resin canals in a cross-section. Regression and path analysis were used to unravel cause-effect relationships between tree characteristics and frankincense yield. Frankincense yield was independent of the actual radial growth rate, but increased with increasing total resin-canal area in the bark, stem diameter, tree age, and the number of leaf apices. We show that frankincense yield by trees is not only a simple function of tree size. Remarkably, trees that grew slower over their whole life history produced more frankincense, suggesting an intra-specific trade-off in growth rate and frankincense production. Overall, this study thus shows that frankincense production is the result of complex plant trait networks and long term tree life properties. The results contribute to management regimes that minimize the damage to trees, while maximizing benefits in terms of frankincense yield and can also be used for selection and propagation of trees which are well suited for frankincense production. [ABSTRACT FROM AUTHOR]

Abstract: African pencil cedar (Juniperus procera Hochst. ex Endlicher 1847) is a tropical, irregularly growing species that can produce annual growth rings in response to an annual cycle of wet and dry seasons. In this paper, we assess the periodicity of growth-ring formation for 13 stem discs from a site in Central-Northern Ethiopia by crossdating and radiocarbon dating. The crossdating process is described more transparently than usual to allow open discussion of the methodology employed. Although the ring-width series could be tentatively matched, radiocarbon dating revealed that the growth rings of the junipers from the studied site are neither annual nor represent a common periodicity. It was found that the trees are exceptionally sensitive and respond individually to the complex local climate. For future research, it is recommended to select more mesic sites with an unambiguously unimodal rainfall regime and to gain external evidence to support assumptions about the periodicity of growth-ring formation in Juniperus procera. [Copyright &y& Elsevier]