The distribution and regeneration of Boswellia papyrifera (Del.) Hochst. in Eritrea

Boswellia papyrifera (Del.) Hochst. is a deciduous gum-producing multipurpose perennial tree species growing in Sudanian and Sahelian regions. The tree is tapped on the stem for oleo-gum called olibanum (true frankincense). Land clearing for agriculture and un-regulated grazing are threatening the future of the natural Boswellia woodlands in Eritrea. Against this background, a study was carried out to investigate the distribution of the species and the factors determining its distribution in Eritrea, to study the structure and dynamics of Boswellia populations, including the natural regeneration, and to identify the factors causing the decline of Boswellia woodlands and measures which can reverse this situation. At macro-level, the distribution of the species was found to be limited to the southwestern and southern parts of the country between 800-1850 m altitude receiving a mean annual rainfall of 375-700 mm with a dependable length of growing period of 45-100 days. At micro-level, the abundance and distribution of the species was found to be affected in order of importance by altitude, land use intensity, soil organic matter, and to a lesser extent by silt and pH. Tree development studies showed that trees in the lowlands were twice as high as those in the highlands. The most important outcome of the population structure study is the lack of regeneration. Out of five areas investigated regeneration was only found at two sites where trees were not tapped and which were not accessible to livestock. Further research showed that the present system of intensive annual tapping throughout the dry season leads to low production of non-viable seeds and that where viable seeds are produced, seedlings and saplings are usually destroyed by livestock. Establishment of enclosures in which tapping and grazing is not allowed were found to be an effective measure to promote natural regeneration. Further research is needed to refine this system and to investigate the feasibility of replanting former Boswellia areas.