Resin secretory structures of Boswellia papyrifera and implications for frankincense yield

Frankincense, a gum-resin, has been tapped from Boswellia papyrifera trees for centuries. Despite the intensive tapping and economic interest of B. papyrifera, information on the resin secretory structures, which are responsible for synthesis, storage and transport of frankincense, is virtually absent. This study describes the type, architecture and distribution of resin secretory structures of B. papyrifera and its relevance for the ecophysiology and economic use of the tree. The type and architecture of resin secretory structures present in bark and wood was investigated from transversal, tangential and radial sections of bark and wood samples. The diameter and density (number of resin canals mm(2)) of axial resin canals were determined from digital images of thin sections across the different zones of inner bark. Resin canals form a three-dimensional network within the inner bark. Yet, the intact resin-conducting and producing network is on average limited to the inner 66 mm of the inner bark. Within the inner bark, the density of non-lignified axial resin canals decreases and the density of lignified resin canals increases from the vascular cambium towards the outer bark. In the wood, only radial resin canals were encountered. Frankincense tapping techniques can be improved based on knowledge of bark anatomy and distribution and architecture of resin secretory structures. The suggested new techniques will contribute to a more sustainable frankincense production that enhances the contribution of frankincense to rural livelihoods and the national economy