Distribution of the frankincense tree Boswellia papyrifera in Eritrea: the role of environment and land use

Abstract

Aim We determined the present and past distribution, and the abundance, of Boswellia papyrifera in Eritrea, and the environmental and land‐use factors determining its distribution limits. Location Eritrea, in the Horn of Africa. Methods In 1997 a Boswellia field survey was conducted in 113 village areas covering four administrative regions. Species occurrence was related to rainfall, air temperature and length of growing period. Additionally, the relationship between the abundance of Boswellia trees and selected physical and chemical soil factors, topography and land‐use types was determined for five study areas (with a total of 144 plots) situated along an altitude gradient of 800–2000 m a.s.l. Results The geographical distribution of B. papyrifera was limited to the south‐western and southern parts of the country between 800 and 1850 m altitude receiving a mean annual rainfall of 375–700 mm, with a growing period of 45–100 days. Species abundance was affected by, in order of importance: altitude, land‐use intensity and soil organic matter. Most trees were found in hilly areas; tree density increased from the foot slope to the hill summit; no trees occurred in valleys. Land‐use intensity, especially agriculture, fallow and grazed areas, had a profound negative effect on tree abundance. Natural regeneration of the species was promoted in areas where grazing by livestock was not allowed or regulated. Main conclusions The distribution of B. papyrifera in Eritrea has decreased during past decades, mainly due to an increasing human population, resulting in the conversion of woodlands into agricultural fields and increasing livestock pressure hindering natural regeneration. Consequently, Boswellia trees are found mainly in hilly areas on steep slopes with shallow soils of low fertility. The species appears to be able to adapt to these harsh growing conditions: in adjacent countries it was also found in comparable growth habitats.

Frankincense production is determined by tree size and tapping frequency and intensity

“…The two regions are at relative extreme and opposite environmental and climatic conditions, with Abergelle characterized by a higher altitude, drier, colder and more intensively sun-lit site conditions than Metema (Mengistu, 2011). B. papyrifera dominated forests cover an area of 330,000 ha in Tigray and 604,000 ha in Amhara, and are mostly found in deciduous woodlands occupying sites with very shallow soils, steep rocky slopes, lava flows or sandy river valleys (Eshete, 2002;Fichtl and Admasu, 1994;Teketay, 2000; see also Ogbazghi et al, 2006a). The four study populations also differ in species composition, diversity and structure .…”

Diversity and production of Ethiopian dry woodlands explained by climate- and soil-stress gradients

“…Awas (2007) had also found similar results where soil variables significantly affect the species composition in lowland woodlands of western Ethiopia. Our woodlands were dominated by B. papyrifera, as were large areas in Ethiopia and Eritrea (Abiyu et al, 2010;Gebrehiwot, 2003;Ogbazghi et al, 2006b) and Sudan (Chikamai, 2002). This dominant species largely differed in population structure from the rest of the community.…”

Fine-scale spatial genetic structure in the frankincense tree Boswellia papyrifera (Del.) Hochst. and implications for conservation

“…The species is an important source of frankincense, a highly valued aromatic resin obtained from the bark of the trees. Due to its use in the production of perfumes and pharmaceuticals, frankincense is internationally traded and is one of the export commodities of Ethiopia, Sudan and Eritrea (Coppen 2005;Lemenih 2005;Ogbazghi et al 2006;Abtew et al 2012). In Ethiopia, B. papyrifera tree stands occur mainly in the North, Northeast, Northwest and Western parts of the country (Eshete et al 2011;Girma et al 2013) and in Combretum-Terminalia and Acacia-Commiphora woodlands.…”