* Endemic to the country or region indicated

Criteria for inclusion, 1. What is a desert tree?

Given that none of the numerous existing definitions perfectly fit our purposes, we made up our own, combining elements from the definitions offered by Shreve and Wiggins (1951), Felger et al. (2001), and Schatz (2001). Our definition is as follows:

In the context of drylands, trees are long-lived plants that develop one sturdy long-lived trunk, from one to 20 meters or more in height. However, individuals subjected to cutting, burning, or browsing, may develop a more multi-stemmed, shrubby appearance.

Examples includes many species of well-known genera such as Acacia (s.l) and Prosopis (Fabaceae), Eucalytpus (Myrtaceae), Commiphora (Burseraceae), Tamarix (Tamaricaceae) and Terminalia (Combretaceae).

In the evolutionary ecology of desert and dryland trees, succulence also merits special attention as it occurs in leaves and young stems, but also in tree trunks (and roots), producing bottle trees (also called pachycaul trees). To underscore the spectrum of life forms and taxonomic groups in which they occur, we use names such as ‘monocot tree’, ‘dwarf tree’, ‘bottle tree’, or ‘arboreal cactus’ when a dryland tree deviates from standard forestry or colloquial notions of trees.

Dwarf trees, candelabra trees, tree succulents, and monocot trees—those without lignified stems—are all included as unusual, but valid categories of desert trees. Typical examples are Adansonia, Aloidendron, Euphorbia, Pachypodium, Phoenix, and Welwitschia.

Criteria for inclusion, 2. Bioeographical factors.

We only included species that have been recorded in areas that receive less than 400 mm of average annual rainfall (Keeping in mind the fact that in drylands, inter-annual variability of rainfall increases in correlation to increasing aridity). Precise rainfall information for remote desert areas are often hard to come by, so we separated areas receiving 0 to 150 mm (hyper-arid), 150 to 250 mm (arid) and 250 to 400 mm (semi-arid). And while many of our species are exclusively found in such arid or semi-arid areas, many others also occur under wetter conditions. In particular, many are also found in desert fringes, which receive between 400 and 600 mm of rainfall. Finally, some trees, particularly in Africa and Australia, range from true deserts to wet or very wet areas, with more than 800 mm of annual rainfall.

Besides elevation, we provide further information about the major habitat types that our species favor, from coastal lagoons (as several mangroves occur on desert coasts), along river courses, to dune fields, and outcrops and inselbergs, or even special formations such as termite mounds. We also indicate the types of substrates on which our species can grow, with further information on underlying rock types. Equally important are the types of vegetation communities in which the different species are typically found, from grasslands to wet montane forests. species, as well as occasional discussion of species whose native range is not known with certainty.

As for geographical range of distribution, we provide large regions of continental or subcontinental scale, such as East Africa, Central Asia, or Australasia. We also include a more detailed account of the countries in which a species occurs, with only a mention of the countries at the edges of the range for particularly widespread species.

We also indicate whether a species is endemic to a single country and a general assessment of its abundance, as well as the official IUCN Redlist threat assessment. NB. Only 661 of our 1578 species have been assessed as of August 2019).

As for morphological characteristics that are typical of arid lands, we provide mention of species that are spiny, as well as some discussion of succulence and typical leaf duration (i.e., deciduous or evergreen).

We also indicate all the known uses that the trees can have for desert-dwelling human populations, given in broad categories, from timber and fuel, to medicinal uses, to nitrogen fixing and soil protection. 

We describe the average height range, as well as occasional exceptional heights that can be reached by individuals in favored positions. We also indicate where a species has the capacity to resprout and whether it is tolerant to salt, frost, and / or fire. When available, we also indicate broad categories describing the species’ lifespan, “Short” refers to species that typically live less than 50 years; “Medium”,  for species that live between 50 and 200 years, “Long” for species that reach 200 to 500 years of age, and finally “Very long” for species that live over 500 years.

For managers, we indicated known effective propagation techniques, such as direct seeding, cuttings, or suckers. We also indicate where species respond well to lopping, coppicing, or pollarding.

Finally, we indicated whether the species has the potential to be invasive outside of its native range.

We do not provide full bibliographic references consulted as that would take up a huge amount of space and readers can find up to date info and most or all of the references we used on the internet with little difficulty. Some of the score of useful websites that we consulted include Trees of Namibia, Living Atlas of South Africa, Flora del Norte de Chile, Useful Tropical Plants, and of course Tropicos.

Over the past thirty years, Edouard, James and Thibaud have taken field trips to various of these arid and semi-arid lands, some of which you can read about on the MoBot website “Natural History of Ecological Restoration”, (see direct link to our posts here). Also, for those who read French, see Les Arbres des Déserts, a semi-popular book on this same subject, published back in 2013, with special emphasis on the Old World deserts.

Together with other colleagues, including Pete Phillipson, administrator of this site, we’ve published several scientific articles on desert trees that you may find of interest. Two of these are available for downloading at these links: Desert trees of SW Madagascar and Enigmatic trees of the Middle East.

Now, we are midway through the writing of a more comprehensive, richly illustrated book in English, to accompany this database.

In addition to referring to our database of desert trees, we write about the tree canopies once common and extensive in some arid and semi-arid lands, and still found in some areas, such as parts of Peru and Namibia, and more extensive tracts in relatively well-conserved areas like the Great Western Woodlands of Western Australia (Photo 3). We discuss this history of transformation and degradation as well as efforts currently underway to restore healthy dryland ecosystems for present and future generations.