| Scientific Name | Aloidendron pillansii (L.Guthrie) Klopper & Gideon.F.Sm. | Higher Classification | Monocotyledons | Family | ASPHODELACEAE | Synonyms | Aloe pillansii L.Guthrie | Common Names | Bastard Quiver Tree (e), Baster-kokerboom (a), Die Lange (a), False Quiver Tree (e), Giant Quiver Tree (e), Reusekokerboom (a), Reuse-kokerboom (a) |
National Status | Status and Criteria | Critically Endangered A4ace | Assessment Date | 2022/05/26 | Assessor(s) | E. Swart, D. Raimondo, C.J. Geldenhuys, C. Rodgerson, P.C.V. Van Wyk, S. Loots, C. Eastment & D. Guo | Justification | This arid adapted tree aloe occurs in the Gariep Centre of Plant Endemism, the richest centre of succulent plant endemism in the world (Van Wyk and Smith 2001). It has a limited distribution in the northern Richtersveld and southern Namibia and has an extent of occurrence (EOO) of 2718 km² and an area of occupancy (AOO) of 316 km². There has been observed declines to the population as a result of drought and illegal collection for the succulent horticultural trade. One of the three subpopulations has also experienced excessive predation by wild fauna and livestock as a consequence of extreme habitat degradation within the southern part of its range, leaving animals little choice but to predate this species. This long-lived species has a generation length of at least 150 years. From available data the population is inferred to have declined by 61% in the past two generations and is predicted (based on climate change models) to decline by a further 92% by the year 2080. This species therefore qualifies for listing as Critically Endangered under criterion A. |
Distribution | Endemism | Not endemic to South Africa | Provincial distribution | Northern Cape | Range | The Giant Quiver Tree is confined to the northwestern part of South Africa and southern part of Namibia. There are three subpopulations, one that occurs in Namibia around Rosh Pinah, a second from the central Richtersveld area, and a third from around Eksteenfontein in the southern parts of the Richtersveld. Most of the individuals occur within the AiAis-Richtersveld Transfrontier Park (Van Jaarsveld 2011). A key factor influencing the distribution of this species is the presence of precipitation in the form of fog during winter months (Loots and Mannheimer 2003). |
Habitat and Ecology | Major system | Terrestrial | Major habitats | Goariep Mountain Succulent Shrubland, Central Richtersveld Mountain Shrubland, Western Gariep Hills Desert, Richtersveld Sheet Wash Desert, Richtersberg Mountain Desert | Description | Plants grow predominantly in the Succulent Karoo biome and occur as solitarily individuals or in small locally abundant groups with clusters varying from 1 to 345 individuals (Swart and Hoffman 2013). They are usually found in open, exposed, rocky terrain on varied geological formations including dolomite, shale, sandstone, or granite. The terrain varies from mountain slopes to flats but the majority of the population occurs on slopes facing east and west. Rainfall ranges from 50-100 mm per annum though droughts in the 21st century have yielded no rain in some localities. Plants grow from 120 to 1,100 m asl. Flowering during spring (October) the species is pollinated mainly by sugarbirds but other birds and bees may also play a role. Capsules ripen and seed is dispersed during summer (Van Jaarsveld 2011). Flowering does not occur during periods of drought.
Heat tolerance is remarkable in the species which inhabits the climatically severe Richtersveld in South Africa and Namibia, where summer temperatures can exceed 50°C (Cousins and Witkowski 2012). There is significant variation in climatic conditions (e.g. summer and winter rainfall regimes, availability of fog precipitation) across the distribution and thus the micro habitat niche (e.g. nursery vegetation and slope aspect) is considered an important an influence on population regeneration which occurs every 50-70 years (Swart and Hoffman 2013). Seeds germinate successfully between 15°C and 25°C with >80% germination rate in the northern and >90% in the central and southern population. Seeds only remain viable for between two and five years and extended periods of drought will thus have a negative impact on seedbanks.
The Giant Tree Aloe, is regarded as a keystone species being one of the few perennial plants able to tolerate extreme drought and heat conditions in the region. It is an important source of shelter, nectar, food and moisture, especially to avifauna. Adults contain large water reserves, which a number of species rely on during periods of extended drought, as well as providing vantage points for raptors in an otherwise sparsely vegetated landscape (Midgley et al. 1997, Powell 2005, Duncan et al. 2006)
Growing up to 12 m height for a possible maximum of 450 years (Duncan et al. 2006), the generation length of this species is considered to be in excess of 150 years. This species does not resprout after mechanical damage. |
Threats | | Decline to the central subpopulation as a result of illegal collection for the succulent horticultural trade has been observed in the past (Duncan et al. 2005, 2006; Powell 2005). Both the northern and central subpopulations are experiencing ongoing habitat loss and degradation as a result of mining activities. The footprint of mines as well as secondary impacts from mining activities such as windblown sand dumps and sand blasting is expected to increase over the next 50 years. An influx of people may also lead to future poaching taking place.
The extreme droughts of the 21st century haxs caused decline to the population. The influence of anthropogenic climate change on rainfall regimes and extreme temperatures are considered a key current and future threat (Swart and Hoffman 2013, Van Wilgen 2016). The prolonged drought that started in 2016 and is still ongoing at the time of this assessment has caused mortality of mature individuals in the central and southern subpopulation, furthermore drought conditions and the general lack of forage available in the broader landscape has led to a significant increase in predation by baboons with these impacts particularly severe for plants occurring in the southern subpopulation. Drought events and their negative influence on grazing/browsing availability in combination with high concentrations of livestock have increased pressure on the juvenile population across this species range. Furthermore, modelled climate envelopes for the time period 2061-2080, show little to no overlap with the current species range (supporting information). These models predict that the pressure from climate change is likely to continue to cause significant population decline. |
Population | The population has three distinct subpopulations (northern, central and southern) each with differing climatic and habitat characteristics. The total population number was estimated to be around 5935 with 1891 of those individuals subject to an ongoing monitoring effort (Swart and Hoffman 2013). Discovery of a few additional stands of plants since 2013 means that the population can be confirmed to be more than 5935 individuals but less than 9 000 individuals.
The northern subpopulation in southern Namibia is senescent, it has the highest density of individuals with 46% of the overall population occurring here. It receives the highest concentration of winter rainfall and fog. This subpopulation occurs predominantly on east and south-west facing slopes and receives the coolest average annual temperature. There is a 4.6:1 ratio of dead to live individuals (77% of known individuals are dead). The majority of the live individuals are adults between 3 and 7 m tall (Swart and Hoffman 2013). There are no seedlings and very few juveniles. While dead skeletons persist for long periods of time, and the rate of decay is not known, this species has a very long generation length of over 150 years, the proportion of dead individuals are therefore assumed to represent those that have died in the past two generations (300 years). This subpopulation has therefore declined by at least 70% over the past two generations.
The central subpopulation constitutes an estimated 16% of the population and occurs mainly in and on the outskirts of the Richtersveld Transfrontier Park. This subpopulation has the lowest density of individuals in comparison to the other two subpopulations. Plants occur on all slope aspects and receive both winter and summer rainfall. For every two live individuals there is one dead skeleton, this subpopulation has a higher concentration of juvenile individuals than the northern population (Swart and Hoffman 2013). It is subject to significant recent threat from stock overgrazing and illegal collection for the horticultural trade. There has been extensive monitoring at one of the stands within this subpopulation that occurs at Cornellskop which constitutes around 5% of the individuals from this central subpopulation. A study in 2006 noted that the number of mature individuals at Cornellskop had halved between 1937 and 2004 (Duncan et al. 2006). This same study showed there to be an annual mortality of 1.4% for individuals above 3 m leading to the conclusion that within 60 years there will be no more adults on Cornellskop. While this stand of individuals does have recruitment taking place (juveniles and seedlings were observed to be present), there has also been a significant loss of small individuals to illegal poaching with 10-15% of juveniles stolen in one year. Cornellskop has since 2018 also been losing habitat to large movement of sand, with the western slopes now covered in sand. This is a new form of habitat change that started in 2015 and occurs as a result of loss of vegetation cover from drought and overgrazing, and changes in wind direction and frequency linked to ongoing climatic change within the Richtersveld region. In other parts of the central subpopulation between the years 2017 and 2020 a number of mature individuals were observed to have died as a result of the severe and prolonged drought that took place between 2015 and 2019. At Five Sisters, another stand in the central subpopulation, 70% of individuals that were alive in 2007 had died 2020. Given these observations of recent declines and decline of 70% of this central subpopulation over the past two generations (300 years) is also inferred.
The southern subpopulation, that constitutes an estimated 38% of the population, is blocked off from winter precipitation due to its location east of the Stinkfontein mountains. This subpopulation receives the highest average annual temperature. Plants grow predominantly on east and west aspects. There were almost 4 live individuals for every dead skeleton here and the population was considered to be growing prior to 2015 due to a high concentration, almost 50% of the subpopulation, consisting of seedlings and juveniles (Swart and Hoffman 2013). Unfortunately, there has been high mortality between 2015-2020 which has been caused by predation from baboons. Monitoring of individuals present in 2006 indicated that by 2014 6.4% had died while by 2020 48.8% of the 2006 individuals had died. This reflects that the drought that took place from 2016-2020 has caused increases in mortality.
Given the above data the population is inferred to have declined by at least 61% over the past 300 years (two generations). Future declines to the population are extremely likely since modelled climate envelopes for the time period 2061-2080, have very low overlap with the current species occupied habitat (supporting information). Climate models for the likely emission scenarios where emissions stay at present day levels (RCP 2.6) (Hausfather and Peters 2020) and worst-case scenarios where emissions continue to increase during the 21st century (RCP 8.5) indicate that there will be a loss of suitable bioclimatic envelope of between 92% and 100% between 2061 and 2080.
| Population trend | Decreasing |
Conservation | | The species is listed in CITES Appendix I (CITES 2019), and is recorded in 25 ex situ collections (BGCI 2020).
A large portion of the population falls within the Ai /Ais-Richtersveld Transfrontier Park where active management, protection and monitoring is possible.
Key research questions include the need to understand rates of decay of carcasses to inform interpretation of the ratio of live to dead individuals. This is a key factor in understanding relative population trend with this long lived species. The ability to respond to climate change is limited by the populations ability to disperse which in turn depends on seed dispersal. Past and current levels of dispersal needs to be better understood by conducting a genetic analyses of the meta-population. A population viability model needs to be constructed using in field repeat monitoring data collected over the past 10 years this will allow for improved predictions of the rate of future declines. |
Notes | | The illegal removal of wild Quiver Trees (Aloidendron dichotomum, A. pillansii and A. ramosissimum) from the Northern Cape was a threat prior to 2016 (Duncan et al. 2005, 2006; Powell 2005), since 2016 there has been a shift to poaching smaller species of succulents and no recent incidence of poaching quiver trees has been recorded. |
Assessment History |
Taxon assessed |
Status and Criteria |
Citation/Red List version | | Aloidendron pillansii (L.Guthrie) Klopper & Gideon.F.Sm. | EN B1ab(iii,v) | 2014.1 | | Aloe pillansii L.Guthrie | EN B1ab(iii,v) | Raimondo et al. (2009) | | Aloe pillansii L.Guthrie | CR A2ace | Victor (2002) | | Aloe pillansii L.Guthrie | Endangered | Hilton-Taylor (1996) | |
Bibliography | Grace, O.M., Klopper, R.R., Smith, G.F., Crouch, N.R., Figueiredo, E., Rønsted, N. and Van Wyk, A.E. 2013. A revised generic classification for Aloe (Xanthorrhoeaceae subfam. Asphodeloideae). Phytotaxa 76(1):7-14.
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Klopper, R.R. and Smith, G.F. 2007. The genus Aloe (Asphodelaceae: Alooideae) in Namaqualand, South Africa. Haseltonia 13:38-51.
Michler, L.M., Treydte, A.C., Hayat, H. and Lemke, S. 2019. Marginalised herders: Social dynamics and natural resource use in the fragile environment of the Richtersveld National Park, South Africa. Environmental Development 29:29-43.
Midgley, J. 1997. The decline of Aloe pillansii at Cornell's Kop in the Richtersveld. Aloe 34(1&2):39.
Midgley, J., Cowling, R.M., Hendriks, H., Desmet, P.G., Esler, K.J. and Rundel, P. 1996. Tree Succulents in the Richtersveld. Veld & Flora 28:74-75.
Powell, E., Hendriks, H., Clark, B., Pretorius, L., Roderick, J. and Garrett, D. 2003. The plight of Aloe pillansii. Veld & Flora 89(4):150-151.
Raimondo, D., von Staden, L., Foden, W., Victor, J.E., Helme, N.A., Turner, R.C., Kamundi, D.A. and Manyama, P.A. 2009. Red List of South African Plants. Strelitzia 25. South African National Biodiversity Institute, Pretoria.
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Setshogo, M.P. 2005. Preliminary Checklist of the Plants of Botswana 37. Southern African Botanical Diversity Network Report, SABONET, Pretoria and Gaborone.
Van Wyk, A.E. and Smith, G.F. 2001. Regions of floristic endemism in southern Africa. Umdaus Press, Hatfield.
Van Wyk, B.-E. and Smith, G. 2003. Guide to aloes of South Africa. (2nd ed.). Briza Publications, Pretoria.
Van Wyk, B.-E. and Smith, G.F. 2014. Guide to the Aloes of South Africa. (Third ed.). Briza Publications, Pretoria.
Victor, J.E. 2002. South Africa. In: J.S. Golding (ed), Southern African plant Red Data Lists. Southern African Botanical Diversity Network Report 14 (pp. 93-120), SABONET, Pretoria.
Walker, C.C. and Vanden Bon, A. 2018. Aloe pearsonii - a unique species in habitat and in cultivation. CactusWorld 36(1):33-40.
Williamson, G. 1998. The ecological status of Aloe pillansii (Aloaceae) in the Richtersveld with particular reference to Cornellskop. Bradleya 16:1-8.
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Citation | | Swart, E., Raimondo, D., Geldenhuys, C.J., Rodgerson, C., Van Wyk, P.C.V., Loots, S., Eastment, C. & Guo, D. 2022. Aloidendron pillansii (L.Guthrie) Klopper & Gideon.F.Sm. National Assessment: Red List of South African Plants version . Accessed on 2025/01/17 |
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