For more taxonomic information see Thulin (2020).

Boswellia elongata is a frankincense tree endemic  to Socotra Island (Yemen) which is locally widespread yet occurs in strongly fragmented stands. It is a ground-rooted species occurring in semi-deciduous woodlands on limestone and (to a lesser extent) granitic substrates at c. 100–800 m asl. The extent of occurrence (EOO) of B. elongata in Socotra Island is 2,388 km² and the area of occupancy (AOO) is 296 km².

A total of 3,951 adult trees have been inventoried during recent detailed field surveys, carried out in 2020–2023 by local Socotri and external specialists (Mendel University, La Sapienza, Ghent University; Franklinia-funded Boswellia project; Maděra et al. 2022, Maděra et al. 2024), and the total global population in the wild is currently estimated at c. 5,000 trees. The species can be found in about 24 sites across Socotra Island (absent in the Zahr Basin) which constitute about six locations, and the distribution is fragmented with several stands containing only a few trees. The largest stands are in the Haggeher Mountains, medium stands in Homhil and in Momi, and several small isolated stands consist of just a few rapidly dying old trees, and are nearly locally extinct. More than half of the global population (outside of the Haggeher) consist of stands that isolated from each other and several are relatively too small to be viable (severely fragmented).

A rapid decline of this species and impacts of climate change (cyclones of 2015) have been been documented in detail, based on a comparison of satellite images over 70 years for one site (Homhil area; Lvoncik et al. 2020). The main threats for this species were assessed in detail in 2020–2023 (Maděra et al. 2024) and include mainly overgrazing (affecting 66% of the total), use of branches for fodder (46.6%) and climate change (all). Natural regeneration is nearly absent due to the strong impacts of overgrazing, which are largely reversed in fenced exclosure areas (in Homhil and Maleh; Franklinia Project). Resin collection is of relatively lower impact, and the species has a wide range of ethnobotanical uses (Miller and Morris 2004). There is a potential for conservation through agroforestry and improving natural regeneration through excluding or reducing grazing impacts, as there is a proper chance for healthy seed germination in the absence of man-made threats (Hamdiah et al. 2022). The species has also been illegally exported by succulent collectors.

Conservation efforts started in 2005 for B. elongata, yet renewed efforts were done locally in 2020, resulting in increased awareness, local seed germination and reforestation (in Maleh, Diburak and Homhil) and are ongoing.

The species is listed as Endangered due to its restricted distribution (EOO and AOO) and the population is considered severely fragmented, the continuing decline is caused by climate change, overgrazing, illegal collection, collection for fodder and lack of natural regeneration.

Boswellia elongata is endemic to Socotra Island (Yemen) where it is relatively widely distributed, absent only in the central basin and the southern coastal plain. The species has a restricted geographic range with an extent of occurrence of 2,319 km² and an area of occupancy of 296 km². Its geographic range on Socotra is discontinuous, with some severely isolated small stands.

Despite its wide distribution in Socotra Island, Boswellia elongata has a  scattered and fragmented distribution with several isolated small stands; the majority of the areas where this tree occurs are lacking natural regeneration. Some stands are strongly relictual with only a few trees remaining. The population is considered severely fragmented, as more than half of the population is found in small and isolated subpopulations.

During the most recent surveys (2020–2023, Franklinia Project team) a total of 3,951 mature trees were inventoried, and the total global number of B. elongata trees in the wild can be estimated at c. 5,000 individuals. Some of the stands (in total 24 stands are known, corresponding to about six subpopulations) count only small numbers of mature specimens (especially in the west), larger ones like in the Haggeher over a 1,000 trees. Small isolated subpopulations, which also show some morphological differences, can be considered as near to locally extinct, like in the west (Maleh), however, even large populations are not safe from the effects of climate change and over-maturity (Lvončík et al. 2020). The pattern of distribution of B. elongata strongly suggests a long-term decline in the extent and quality of its habitat, and continuous fragmentation.

There are two forms of B. elongata that can be distinguished, the first has green-yellow light coloured flowers and occurs in the eastern part, second has reddish flowers and it is distributed in the west. Subpopulation in the central part of the mountains contains mixed stands (with both colours of flowers). Research is ongoing to determine whether these morphological differences also have a genetic basis.

As a large, ground-rooting frankincense tree, this species is strongly threatened by overgrazing, populations are (over)mature with no regeneration in the wild, and they are clearly declining. Populations of B. elongata were strongly affected by climate change (cyclones), for example in Homhil Nature Sanctuary (Lvoncik et al. 2020), even more than other Boswellia species.

In places where populations of B. elongata are in the proximity of of other Boswellia species, hybridization is possible (for example with B. ameero, B. nana and B. popoviana).

Boswellia elongata belongs to the ground-rooting species of the genus Boswellia. It is a relatively large tree (for the genus) up to 10 m in height and c. 70 cm in dbh (diameter at breast height). Widely scattered in dry, semi-deciduous woodland and less common in succulent shrubland. On both limestone and granitic substrates, at altitudes ranging between c. 90 and 840 m asl. Blooms from March to April (May), flowers are creamy to yellowish-green (in some areas pale pink or red) in long racemes; sometimes blooming also in October/November after rains (winter monsoon). Fruits ripen from May to June. A study on the biology of B. elongata has shown that seed germination rates vary from a few per cent to more than 35 % and a high rate of empty (under developed) seeds was recorded in this species (Hamdiah et al. 2022). There is still a high potential for natural regeneration, in particular after rain from September to November, however seedlings cannot escape browsing (by goats) in their natural surroundings at present. Notes on morphology, ecology and distribution in Miller (1992, 1997), Miller et al. (2004), Attorre et al. (2011), Lvončík et al. (2013) and Thulin (2020), now revised after detailed surveys in situ (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), Madĕra and Van Damme (2022). The challenges specifically to the endemic Boswellia in Socotra are reviewed in Maděra et al. (2024). The specific threats to B. elongata have been assessed in detail in situ in 2020-2023 (Franklinia Project team; Maděra et al. 2022, 2024). These include impacts of climate change, overgrazing and to a lesser extent infrastructure development (roads, houses). Overgrazing was recorded as the highest risk for B. elongata populations, the estimated proportion of the population affected by overgrazing in the areas where it occurs is 66.3% (40.9% high, 19.0% middle and 6.4% low intensity). Also, silvopastoral practices such as branch cutting for livestock fodder affects 46.6% of the entire population (2.5% high, 15.1% middle and 29.0% low intensity). In total, development threatens a smaller proportion of the trees directly (20.0% by road construction; 3% village expansions). Resin harvesting (mostly low intensity) was recorded in 26.6% of the entire population. Lvoncik et al. (2020) carried out a detailed study using satellite images and ground truthing assessing the decline of a B. elongata stand in Homhil Nature Sanctuary in eastern Socotra, where 38% of the trees were directly destroyed by climate effects (cyclones) in 2015, and another 29% from delayed effects of the climate impacts. The study shows clearly how the trees in Homhil Nature Sanctuary are declining at an exponential rate by over-maturity and overgrazing, accelerated by climate change effects. The species has also been illegally exported and sold in international markets by succulent collectors.

Boswellia elongata is highly valuable tree from an ethnobotanical point of view on Socotra, with a wide use (Miller and Morris 2004). The resin is not of high quality, but it is collected and sold in small amounts to tourists in some localities. The indigenous uses of this tree include human medicine (chewing the resin helps to disinfect the oral cavity), as animal food (people cut the leaves as fodder for livestock in the dry season) and for other household uses (to burn resin as incense and insect repellent). The flowers are important for bee foraging and honey production (Miller and Morris 2004).

Specific conservation efforts for this endangered species started already since 2005 in Homhil Nature Sanctuary, and in the entire island (for all Boswellia species) since 2020, including the establishment of local nurseries, awareness, local seed germination and reforestation areas. Two reforestation areas have been established for B. elongata within a project supported by the Franklinia Foundation since 2020 (implemented by local teams in coordination with a consortium of Mendel, Sapienza and Ghent Universities and in cooperation with the local authority EPA). One is in eastern Socotra Island, in Diburak (B. elongata with light-green coloured flowers) and one in the west, in Maleh Plateau (B. elongata with reddish flowers), and these exclosure areas (no grazing) are maintained by indigenous people. The core population in Homhil (more than 1,000 trees) was largely destroyed by cyclones in 2015 and subsequently destroyed by bark beetle attacks (Lvoncik et al. 2020), so some conservation efforts are also ongoing there. Currently the largest population of B. elongata is in Takesh with at least 500 trees. A species action plan and monitoring of the existing populations and their threats, in both isolated stands and areas with more trees are important, considering this large ground-rooting species declines rapidly. Cultivation in home gardens is common and should be supported as one of the possible rescue actions, however overgrazing by goats and impacts of climate change remain major challenges.