Saharan plants: forgotten survivors and global assets
Read here the first article of Sandscript 32nd issue
The Saharan plants, and the landscapes they form, have a deep history reflecting the dynamic history of the Sahara, whether it be the changes after the end of the last African Humid Period (c. 5,000 years ago), the ongoing fluctuations in monsoon systems or the heavy impact of increased agriculture and pastoralism on both oases and rangelands. That dynamism is not frozen but ongoing and highly relevant to the future of the Saharan and Sahelian landscapes and their often-overlooked biodiversity. Plants provide narratives that enforce the status of the Sahara as a global priority for conservation and place the conservation, and restoration, of biodiversity in a long-standing biocultural tradition. The stories of the oryx, ostrich and aoudad are intertwined with stories of ancient cypress trees, lost perennial grasslands, argania groves, and wild watermelon.
From a conservationist’s perspective we can look at three areas of responsibility. Much of the Sahara’s plant diversity is widespread with non-threatened species occurring widely across the region; however, their biomass and composition has been profoundly modified by centuries of grazing. The recovery of these species (and their fungal and bacterial symbionts) provides the substrate for rebuilding the wildlife of the Sahara with the potential to restore above-ground and root biomass, food and nectar resources for wildlife and micro-climate improvements.
There are two additional conservation priorities. The small number of relict and globally threatened plant species that have survived climate change in the Saharan massifs, and the biocultural resources of the Sahara, including wild collected medicinal plants and a fascinating group of species that represent the ongoing legacy of domestication that has produced crops of global importance, such as the watermelon, millet, date, and sorghum.
The Saharan massifs (Hoggar, Tassili, Tibesti, Aïr, Ennedi and the outliers Jebel Marra and Gebel Elba) hold ancient survivors from a wetter Sahara, including fish and crocodiles, and an overlooked group of plants. The Saharan massifs can be described, with some exaggeration, as the Galapagos of the Saharan sea. Some of these plant species are endemic, surviving in one location, such as the famous Saharan cypress Cupressus dupreziana (Endangered – EN) that survives as only 233 wild trees in the Tassili, with some trees as old as 2,400 years. The related Atlas cypress, Cupressus dupreziana ssp. atlantica (Critically Endangered – CR) is restricted to one location in Morocco. Other species survive in several massifs, such as the Saharan wild olive, Olea europea subsp. laperrinei, a close relative of the domestic olive. Some of these mountain species originate from the Mediterranean (e.g. Pistacia, Nerium, Olea, Myrtus and Cupressus) others are of sub-Saharan or Arabian origin (e.g., Acacia, Ficus, Ziziphus, and Maerua).
One fascinating species found in the Saharan massifs is Erica arborea, the tree heath, part of a genus that shows remarkable diversification and local endemism in southern Africa, yet this one species has a range that encompasses the East African mountains, the Saharan massifs, the Mediterranean and the Macaronesian archipelago (Canary and Madeira islands). Whilst the Saharan myrtle, Myrtus nivellei, found in the Hoggar, Tassili, Teffedest and Tibesti, is a Mediterranean colonist that has been restricted to those massifs since at least the last Green Sahara period, around 5,500 years ago. In Gebel Elba, Egypt, there is an outlying and declining population of dragon trees, Dracaena ombet, (EN) a species that is restricted to the mountains of Northeast Africa and Saudi Arabia. It is closely related to Dracaena draco (EN) found in the Macaronesian islands and Morocco. The relictual species of the Saharan massifs are amongst the region’s most threatened species and deserving of greater conservation investment and integration into Saharan conservation initiatives.
Humans have adopted several wild trees as productive elements of the region’s landscapes. Some have developed into globally important crops; others remain locally valued. Gum Arabic, the gum harvested from Acacia senegal and Acacia seyal is part of an ancient trade between the Sahel and Europe. The gum is collected from the diminished band of acacia woodland that once covered much of the Sahel. Gum arabic remains a main export of several African Sahelian nations, including Mauritania, Niger, Chad, and Sudan (traditionally the largest exporter of high-quality gum). Global production of gum arabic is about 120,000 tonnes a year, worth $1.1 billion (2022). The gum is used in cosmetics, medicine, as a component in ink, and most importantly as a stabiliser in the food and soft drinks industry. Currently there is no industrial substitute for gum arabic and the war in Sudan has threatened the supply to major customers such as Coca Cola and Pepsico, who are currently using stockpiled supplies.
Two tree species from the edges of the Sahara are used as cosmetics and retailed widely in Europe, Asia, and North America. Shea butter is harvested from Vitellaria paradoxa, a tree native to the dry woodland belt of the Sahel. To the north of the Sahara another valuable oil is harvested from the Argan tree (Sideroxylon spinosum) endemic to Morocco and Algeria (previously thought to be a monotypic genus Argania spinosa). Given the attractiveness of the Argan fruit to ruminants it is tempting to imagine herds of gazelle and the extinct bubal hartebeest foraging under the trees for the nutritious fruit (now happily consumed by domesticated sheep and goats).
The Sahara has a long agricultural history that has fluctuated with the region’s shifting climate, and like so many aspects of the Sahara’s history it has been influenced by the adjoining Mediterranean, Indian Ocean, Middle Eastern and sub-Saharan African cultures. The domestic watermelon, Citrullus lanatus, an important global crop, originated and was first domesticated in northeastern Africa. Kordofan melons from Sudan have been identified as the closest relatives, and likely progenitors, of the modern watermelon. The sweet, red fleshed watermelon was probably domesticated there and then spread northwards, where it appears to have been consumed around 4,300 years ago. The related wild Citrullus colocynthis is a known food plant and important source of water for many desert ungulates, including the scimitar-horned oryx.
Two globally important cereals have their origins in the Sahara and Sahel. The first known domesticated pearl millet, Pennisetum glaucum, originated in the western Sahelian zone and sorghum, Sorghum bicolor, in the eastern Sudan around 5,000 years ago. The date palm, Phoenix dactylifera, is an ancient domesticate, probably originating in Arabia (possibly Abu Dhabi and Kuwait) about 7,000 years ago. The North African and Saharan varieties, including the well-known cultivars of Medjool and Deglet Noor, show evidence of historical hybridisation with Phoenix theophrasti (Nearly Threatened – NT), a wild species found in Crete and Turkey. Subsequently, the date palm has become an integral part of the Sahara’s heritage and food traditions. In some respects, the date palm echoes the history of another, albeit later Arabian domesticate, that has become part of the culture and economy of the Sahara, the dromedary (Camelus dromedarius).
Saharan plants provide an insight into the impacts of continuing climate change; after millennia the Saharan massifs still hold floristic remnants from a wetter Sahara. These species represent an urgent conservation responsibility. A drier Sahara after the end of the African Humid Period has been a crucible for agriculture, providing new crops to the world, and adopting new crops from outside the Sahara and Sahel. The Saharan and Sahelian landscapes are still in flux, still subject to over grazing, agricultural expansion and charcoal extraction, however, new agricultural and conservation landscapes are emerging. Whatever the future of these dynamic arid landscapes, plants will remain as a vital resource for the restoration of nature and ecosystem services, the definition of living Saharan cultures, and the urgent need to build functioning agriculture in drylands.
Mike Maunder
Biodiversity and Conservation Consultant – MAUNDER CONSULTING
