Thulin (2020) treats Boswellia aspleniifolia s.str. and B. socotrana s.str. as full species, whereas Lvončík and Řepka (2020) distinguish two subspecies of B. socotrana s.l. (B. socotrana subsp. aspleniifolia and B. socotrana subsp. socotrana), here we follow the latter.

Boswellia socotrana s.l. is endemic to Socotra Island (Yemen). Two subspecies are known (B. socotrana subsp. socotrana and B. socotrana subsp. aspleniifolia). For taxonomical discussions on the status of these taxa, see Thulin (2020) and Lvončík and Řepka (2020). Boswellia socotrana s.l. occurs in valleys and highlands in the northeastern, northwestern and a few localities in the central part of Socotra Island. The species has a restricted geographic range with an extent of occurrence (EOO) of 1,455 km², and an area of occupancy (AOO) of 232 km².

Recent surveys of current distribution, number of trees and assessment of threats were carried out in 2020–2023 by local Socotri and external specialists (Mendel University, La Sapienza, Ghent University; Franklinia-funded Boswellia project) in the entire Socotra Archipelago, leading to a detailed and updated inventory of B. socotrana s.l. and both subspecies separately (Maděra et al. 2022, 2024). In total 5,088 trees were inventoried in 2020–2023 and the total of individuals in the wild is estimated currently at 6,500 trees (2,500 of B. socotrana subsp. socotrana and 4,000 of B. socotrana subsp. aspleniifolia). These occur in 14 localities in Socotra Island, which correspond to seven different locations (in some areas, the two subspecies are found together). Some stands consist of a very small number of trees, others are relatively large, such as B. socotrana subsp. aspleniifolia in Shata Qalansiyah and B. socotrana subsp. socotrana in Ayhaft Valley (see Maděra et al. 2024). Stands are discontinuous from one another, and several subpopulations representing entire areas are highly relictual and disappearing rapidly (e.g., only one tree of B. socotrana subsp. socotrana in Firmihin).

There is a continuous decline of this species in most subpopulations of B. socotrana s.l., due to climate impacts (cyclones, drought, landslides) and overgrazing by goats. Natural regeneration is absent in most areas. Recent cyclones (2015) have impacted several areas and uprooted B. socotrana trees recently, while these subpopulations are already over-mature with little to no regeneration. For details, see the assessments of both subspecies and Maděra et al. (2024).

This endemic species is locally highly valued for its resin in Socotra, and has a wide range of ethnobotanical uses (Miller and Morris 2004). Nevertheless, resin collection does not form a threat to the species currently, as the indigenous people collect only the naturally excreted resin and mainly for local use (and small scale income by selling to tourists).

Conservation efforts of B. socotrana s.l. started in 2020, with in situ seed germination experiments (Hamdiah et al. 2022) and the establishment of nurseries and natural reforestation/restoration areas in Shata Qalansiyah (for B. socotrana subsp. aspleniifolia) and Ayhaft Valley (for B. socotrana subsp. socotrana) yields a successful growth of seedlings. More info on distribution, threats and ecology of both subspecies in Maděra et al. (2024). Conservation efforts started in 2020 for B. socotrana s.l., resulting in increased awareness, local seed germination and reforestation (in Ayhaft and Shata Qalansiyah) and are ongoing.

Boswellia socotrana s.l. is assessed as Vulnerable due to its restricted distribution (EOO and AOO) and the population is found in seven locations, the continuing decline is caused by climate change, overgrazing, illegal collection, collection for fodder and lack of natural regeneration.

Boswellia socotrana s.l. is endemic to Socotra Island. It occurs in valleys and highlands in the northwestern, northeastern and (to a lesser extent), central parts of the island. The species has a restricted geographic range with an extent of occurrence (EOO) of 1,455 km², and an area of occupancy (AOO) of 232 km². The population is discontinuous, with strong fragmentation. Boswellia socotrana s.l. occurs in 14 localities in Socotra Island, which correspond to seven different locations (in some areas, the two subspecies are found together). Some stands consist of a very small number of trees, others are relatively large, such as B. socotrana subsp. aspleniifolia in Shata Qalansiyah and B. socotrana subsp. socotrana in Ayhaft Valley (Maděra et al. 2024). Stands are discontinuous from one another, and several subpopulations representing entire areas are highly relictual and disappearing rapidly (e.g., only one tree of B. socotrana subsp. socotrana in Firmihin and one tree in Bitgobihir). There is a continuous decline of this species in most subpopulations due to climate impacts (cyclones, drought) and overgrazing by goats.

Boswellia socotrana only occurs in the northeastern, northwestern and central part of Socotra Island. In total, 5,088 trees have been inventoried from the entire island recently (assessed in 2020–2023; Madĕra et al. 2024), and up to 6,500 individual adult trees can be estimated in the wild. These occur in 14 different localities which correspond to seven distinct areas, therefore the population is highly fragmented. Except for the largest subpopulation in Ayhaft valley, the other subpopulations are over-mature with no regeneration due to overgrazing by goats, and they are slowly declining. Distribution is fragmented, some populations consist of only a few, to sometimes only a single tree remaining (e.g., in Firmihin or Bitgobihir). The exact structure of the subpopulations is unknown and awaits molecular study (ongoing), yet considering some populations are highly isolated, there is a potential for genetic intraspecific diversity (within the two subspecies).

Boswellia socotrana is a ground-rooting species distributed in dry, semi-deciduous woodland (relatively less common in Croton socotranus shrubland) at an altitude of 14–627 m asl, growing on both limestone and granitic substrates. It is a small tree up to 13 m in height and 50 cm in dbh (diameter at breast height), easily distinguished by small pinnate leaves with winged stalks; two distinct subspecies are recognised (Miller and Morris 2004, Lvončík and Řepka 2020, Thulin 2020). Blooms from March to April with creamy or pale yellow flowers in short sparse racemes. Fruits ripen from May to June; recent in situ experiments have shown that seed germination rate of this taxon varies among localities and years substantially, yet it is very high reaching up to 90 % (Hamdiah et al. 2022). Although seedlings are visible after rains in winter monsoon (from September to December) in most areas where it occurs, the strong effect of goat grazing does not allow them to survive. Notes on morphology, ecology and distribution in Miller (1992, 1997), Miller et al. (2004), Attorre et al. (2011), Lvončík et al. (2013), Lvončík and Řepka (2020) and Thulin (2020). Recent revision of ecology, distribution and threats of both subspecies after detailed surveys in situ in 2020–2023 can be found in Madĕra et al. (2024).

The endemic Boswellia species of Socotra undergo general challenges to the archipelago's terrestrial biodiversity as discussed in Van Damme and Banfield (2011), Attorre and Van Damme (2020) and Madĕra and Van Damme (2022). The challenges specifically to the endemic Boswellia in Socotra, including both subspecies of B. socotrana s.l., are reviewed in Maděra et al. (2024). The specific threats to B. socotrana s.l. have been assessed in detail in situ in 2020–2023 (Franklinia Project team; Madĕra et al. 2022, 2024). Major threats include overgrazing by goats, branch cutting (for fodder), climate effects (cyclones, landslides, flash floods, droughts) and nearby infrastructure development (in lowland areas). Details on the proportions of the populations affected by these threats can be found under the individual assessments of both subspecies. For example, overgrazing affects 76.7% of the total population of B. socotrana subsp. aspleniifolia and 86.6% of B. socotrana subsp. socotrana, while climate change effects and branch cutting (for fodder) also play a major role. Road networks and village expansion are likely to negatively affect this species further in the future, as several stands occur in lowlands and/or directly adjacent to main roads. Although this species is of high local value because of its resin (Miller and Morris 2004), there is no negative impact on the trees due to collection by indigenous people who collect only naturally excreted resin (no tapping) from this species.

Boswellia socotrana is a highly valuable tree to the indigenous people of Socotra from an ethnobotanical point of view, with many uses (Miller and Morris 2004). Indigenous people use this tree as a medicine for humans (chewing the resin disinfects the oral cavity), as an animal food (they cut the leaves as a fodder for livestock in dry season and blooming it is excellent for honeybees) and as an other household use (to burn resin as incense and repellent). There is an illegal international market for this species, which is smuggled out by succulent collectors.

Specific conservation efforts for B. socotrana s.l. (and other Boswellia in the Socotra Archipelago) started in 2020, including the establishment of local nurseries, awareness, local seed germination and reforestation. One reforestation area focused on B. socotrana subsp. aspleniifolia natural regeneration has been established in the area with the largest natural population, in Shata Qalansiyah in 2020 within the Boswellia project supported by the Franklinia Foundation (implemented by local teams in coordination with a consortium of Mendel, Sapienza and Ghent Universities and in cooperation with the local authority EPA). Another was established in the same year for B. socotrana subsp. socotrana in Ayhaft Valley under the same project. Both the Shata Qalansiyah and Ayhaft Valley reforestation areas yields a high number of natural seedlings and these areas are maintained by indigenous land owners who are directly involved in all restoration and awareness activities.

For the other subpopulations of B. socotrana s.l., which are smaller and often relictual, it is strongly recommended to take care of regeneration to avoid further rapid decline. A species action plan and monitoring of the existing subpopulations and their threats are important (and underway). Also, cultivation in home-gardens should be supported, and illegal trade by succulent collectors should be monitored. The species has high potential for natural regeneration in the absence of grazing pressure, as in situ experiments indicate a high germination rate (Hamdiah et al. 2022). Further awareness activities should also be stimulated, involving local people.