II.I.X. Boswellia scopulorum Thulin
Boswellia scopulorum is an endemic species on Socotra Island. The name “scopulorum” refers to its cliff-rooting habit. It is a small tree up to 5 m with smooth, light grey bark. Leaves are densely crowded at shoot apices, imparipinnate 3-15 leaflets, 3-18 cm in size, deeply, irregularly serrate. Red flowers are growing in pubescent panicles up to 11 cm long. Fruits are subglobose capsules.
Boswellia scopulorum is a very rare taxon restricted to Socotra Island, where it occurs only in one area (Bitgobihir Mountain) on limestone cliffs in dry, semi-deciduous woodland at an altitude of 81–425 m. The only known population counts 68 trees in total and consists of two adjacent localities, in an EOO of 12 (3.58) km2 and AOO of 12 km², which correspond to a single threat-defined location. There are potentially more individuals on this mountain, however it is difficult terrain to access, and we estimate the current population at around 200 individuals. The population trend is unclear, because this species was only recently described (Thulin, 2020). Due to the inaccessible terrain (growing on vertical rock faces), direct pressure by goat grazing is limited for adult trees. However, seedlings in the surrounding of adult trees have not been observed, indicating strong grazing pressure (the locality is near busy settlements).
Overgrazing is observed in the area (91.2% of the entire population, 48.5% high, 11.8% middle and 30.9% low intensity), and we found traces of resin harvesting (7.4% of the population with low intensity only) as well as direct branch cutting for fodder (10.3% of the population affected, with low intensity only).
According to the IUCN Red List the species is assessed as Critically Endangered – CR B1ab(iii,v); C2a(ii).
Figure. Boswellia scophulorum Thulin
Figure. A: Recorded trees, AOO and EOO; B: subpopulations and localities of Boswellia scopulorum in Socotra Island.