North East African (Somalo-Ethiopian Biozone) Coastal Dune Vegetation

In the Somalian dunes southwest of Mogadiscio about five vegetation zones have been recognised.

Atriplex farinose Pioneer Dunes
This vegetation, dominated by Atriplex farinose, forms a continuous but relatively narrow belt on the seaward limit of the dunes. It is often monospecific but may also include one or two other species such as Aerva lanata and Panicum pinifolium.

Scaevola plumieri Moble Foredunes
Scaevola plumieri is a small shrub that forms closed stands mostly on the slopes of mobile foredunes. However, it is relatively infrequent so only plays a small part in the overall consolidation of dunes in this area. Companion species are psammophytes that are widespread in the dune environment.

Ipomoea pes-caprae Dune Slack
Ipomoea pes-caprae ssp. brasiliensis is the absolute dominant in humid depressions between dunes and on the littoral sand flats where it is occasionally submerged by high tides. It is a rhizomatous geophyte with long creeping runners well adapted to coastal sandy environments and contributes to sand dune consolidation.  Companion species often include other rhizomatous geophytes like Cyperus chordorrhizus and Sporobolus pungens.

Justicia ovalifolia-Polycarpaea somalensis Mobile Dunes
In the first series of mobile coastal dunes the most frequent species are Justicia ovalifolia var. psammophila and Polycarpaea somalensis. The vegetation is never closed and mostly confined to the summit of dunes. Associated species include Aerva lanata, Atriplex coriacea, Boerhaavia repens, Cyperus chordorrhizus, Dactyloctaenium sindicum, Pseudosopubia procumbens, Senecio bellioides and Sporobolus pungens.

Hypoestes carnulosa-Cyperus chordorrhizus Fixed Dunes
Widespread on consolidated sand this association occurs on both calcareous white sand and siliceous red sand. It can occur at elevations up to 60 m on old dunes near Smith Bay but is confined to relatively flat ground or gentle slopes and is often grazed by camels. The most frequent companion species are geophytes such as Dactyloctaenium sindicum, Dipicadi viride and Mariscus somalensis. Less common geophytes are Ipomoea citrina, Jatropha crinata and Rhynchosia velutina. Other species are mainly dwarf shrubs and grasses such as Alysicarpus macalusoi, Blepharis edulis, Boerhaavia repens, Digitaria brunoana, Diodia aulacosperma, Endostemon gracile, Gisekia Africana, Heliotropium arenarium, Hypoestes carnulosa, Indigofera ciferrii, Rhynchosia viscose and Tephrosia uniflora.

East African (Zanzibar-Inhambane Biozone) Coastal Dune Vegetation (Kenya)

This active, prograding dune system includes transitions to more stabilized dunes. The area behind the active dune field is a complex fossil dune ridge system. However, parts of these dune are too dry to support vegetation. Even in this tropical humid climate dry conditions are experienced due to the high evaporation rates, which are almost double the annual precipitation rates. The following dune zones have been described (Abuodha et al. 2003

Foredunes and Embryonic dunes
Foredunes are a distinctive feature. The main pioneer plants are Halopyrum mucronatum in the north and Ipomoea pes-caprae south of the Sabaki River, both of which are succulent species. With the latter companion species include Hermbstaedtia gregoryi and Scaevola plumieri. All the above species are also associated with deflation plains in the north where there scattered embryonic dunes.

Primary Dunes
These are largely colonised by shrubs but can be divided in to dunes characterised by the low shrub Cordia somaliensis and those dominated by the herbaceous Tephrosia purpurea. Other shrubs associated with Cordia somaliensis include Cadaba farinosa, Calotropis procera, Maytenus senegalensis and Pluchea discordis. These often form a single dense layer up to 5 m high which is usually infested with the parasitic vine Cassytha filiformis. The ground layer includes various shrubs such as Justicia flava and Sideroxylon inerme and grasses like Digitaria argyrotricha, D. gazensis and D. nuda. Other species associated with Tephrosia purpurea dunes include forbs such as Ipomoea pes-caprae and Macrotyloma uniflora and the grasses Digitaria argyrotricha and Eragrostis ciliaris.

Stabilized Hummock Dunes
The main species here is Cordia somaliensis, but they are also thickly vegetated with other shrubs such as Azima tetracantha, Phyllanthus reticulatus and Pluchea discoridis. Other shrubs include Achyranthes aspera, Commelina latifolia and Justicia flava. In the herbaceous layer Asystasia gangetica is the most abundant species, but graminoids such as Cenchrus biflorus, Digitaria argyrotricha, D. gazensis, D. nuda and Eragrostis ciliaris also occur. Also present are climbers such as Cissus rotundifolia, Jasminium fluminence and momordica rostrata.  

Dune Ridges
On the ridges of some of the more stabilized dunes relatively rich vegetation has developed often dominated by the shrub Cordia somaliensis.  Two communities have been identified – one characterised by Cordia somaliensis and Pluchea discoridis, the other by Achyranthes aspera and Justicia flava. The first is composed of medium to tall shrub with occasional trees. Other shrubs include Azima tetracantha, Deinbollia borbonica, Dichrostachys cinerea, Maytenus senegalensis, Phyllanthus reticulatus and Tricalysia ovalifolia. Typical trees mainly confined to the more sheltered zones include Afzelia cuanzensis, Drypetes natalensis, Garcinia livingstonei and Sideroxylon inerme. The second community is described as a herb layer beneath the Cordia somaliensis and Pluchea discoridis community. Other companion herbs include Asystasia gangetica, Boerhavia diffusa together with a few grasses such as Digitaria argyrotricha and Eragrostis ciliaris.

Dune Slacks
These low-lying depressions close to the water table are relatively species rich with most of the plant species being forbs or grasses. Two communities have been identified – one characterised by Tephrosia purpurea and Halopyrum mucronatum and the other by Pluchea discoridis and Portulaca parensis.   The first one occurs in areas where the water table is more than 0.5 m deep. The vegetation is xeromorphic in character and typically includes the grasses Digitaria argyrotricha and Eragrostis ciliaris. The latter community is typical of areas where the water table is less than 0.5 m. The shrub Pluchea discoridis mainly occurs south of the Sabaki River while the succulent herb Portulaca parensis is mainly north of the river. Other herbs include Alysicarpus glumaceus, Desmodium triflorum, Enicostema axillare, Hermbstaedtia gregoryi, Polygala sphenoptera and Stylosanthes fruticosa. Sedges such as Cyperus articulatus, C. rotundus, Fimbristylis cymosa, Pycreus polystachyos and Typha domigensis are also common.

East African (Zanzibar-Inhambane Biozone) Coastal Dune Vegetation (Mozambique)

The coastal dunes of this zone normally include a pioneer zone of sand binding species that eventually creates conditions suitable for a dune thicket. This in turn slowly allows the development of dune forest. Along the Mozambique coast the main pioneer species are Canavalia maritima, Cyperus maritimus, Dactyloctenium aequptiacum, Ipomoea pes-caprae, Launaea sarmentosa, Scaevola thunbergii, Sesuvium portulacastrum, Sophora tomentosa, Sporobolus virginicus, Tephrosia canescens and the endemic Sophora inhambanensis. Other endemic species associated with these dunes are the shrubs Cussonia arenicola (Araliaceae) and Fagara schlecteri (Rutaceae), and the herbaceous species Cleome stricta (Capparidaceae), Hermannia micropetala (Sterculiaceae), Polygala francisci (Polygalaceae) and Tricliceras lanceolatum (Turneraceae).  Moving landward into the dune thicket zone there is a degree of variation in species composition. In southern Mozambique there is often a dense low cover of the endemic bush Grewia occidentalis var. littoralis (Malvaceae), while in more southerly areas Mimusops caffra is usually the dominant shrubby species. The endemic species of these coastal thickets include the shrubs Elaeodendron fruticosum (Celastraceae) and Memecylon sessilicarpum (Melastomataceae), the climber Triaspis suffulta (Malpighiaceae), and the perennial herbs Krauseola mosambicina (Caryophyllaceae) and Spermacoce schlecteri (Rubiaceae). With increasing stabilisation species such as Apodytes dimidiata, Brachylaena discolor, Bridelia schlecteri, Clerodendron glabrum, Commiphora schlecteri, Ochna natalitia, Ozoroa obovata and Vepris lanceolata become more important. In some cases these have developed into dense evergreen forests rich in climbers and lianas such as Maclura africana, Popowia caffra, Rhoicissus revoilii, Sarcostemma viminale, Uvaria gracilipes and the endemic Cissus quadrangularis (Vitaceae), while other endemic species of these dune forests include the shrubs Allophylus mossambicensis (Sapindaceae) and Jatropha subaequiloba (Euphorbiaceae).

South East African (Tongoland-Pondoland Biozone) Coastal Dune Vegetation

In this zone most authors distinguish four vegetation zones based on physiognomy

Pioneer Coastal Dune Vegetation
Here sand binding plants create condition suitable for sand to accumulate and starting the initial stabilisation process. The most common pioneer species is the efficient sand binder Scaevola plumieri whereas other species such as Arctotheca populifolia, Gazania rigens var. uniflora and Hydrophylax carnosa occur more sporadically. Pioneer species like Carpobrotus dimidiatus and Ipomoea pes-caprae ssp. brasiliensis also become established as stabilisation proceeds.  

Passerina Coastal Dune Scrub
Characterised by Passerina rigida, this vegetation represents the first woody zone to establish on new dunes. It is frequently accompanied by other shrubs and grasses such as Sporobolus virginicus. Other species such as Helichrysum kraussii and Imperata cylindrical become more important in the northern parts of this biozone.

Coastal Dune Thicket
The seaward slopes of older dunes are usually covered in a dense, stunted thicket up to 5m tall. Typical species include Allophylus natalensis, Brachylaena discolour ssp. discolour, Chrysanthemoides monilifera, Calpoon compressum, Eugenia capensis, Maytenus nemorosa and Mimusops caffra. However, the field layer is virtually devoid of species.

Coastal Dune Forest
These forests contain a unique combination of plants and animals and seem to be confined to the ancient coastal dunes of northern KwaZuluNatal and the extreme southern part of Mozambique (Maputaland). Dominant trees include Brachylaena huilensis, Cleistanthus schlechteri, Dialium schlechteri, Hymenocardia ulmoides, Manilkara discolor and Pteleopsis myrtifolia, while common understory shrubs are Drypetes arguta, Drypetes natalensis, Leptactinia delagoensis ssp. delagoensis, Monodora junodii, Todalliopsis bremekampii and Vitex amboniensis. There are also many characteristic lianas such as Secamone delagoensis and Uvaria lucida. On dune slopes and interdune depressions the tall tree Balanites maughamii and the understory shrub Cola greenwayi are well represented together with various endemic species such as the trees Haplocoelum gallense (Sapindaceae), Wrightia natalensis (Apocynaceae), and the creepers Acacia kraussiana (Mimosaceae) and Strophanthus luteolus (Apocynaceae). On dune crests and in some dune depressions, there are endemic shrubs such as Grewia microthyrsa (Tiliaceae), Hyperacanthus microphyllus (Rubiaceae), Oxyanthus latifolius (Rubiaceae) and Psydrax fragrantissima (Rubiaceae) together with trees such as the endemic Combretum mkuzense (Combretaceae). However, these forests support a multitude of other endemic taxa like Aneilema arenicola (Commelinaceae), Barieria prionitis ssp. delagoensis (Acanthaceae), Bonatea lamprophylla (Orchidaceae), Cleome bororensis (Capparaceae), Crassula maputensis (Crassulaceae), Encephalartos ferox (Zamiaceae) and Pavetta gerstnerii (Rubiaceae) just to mention a few.

West African Coastal Dunes

Pioneer Vegetation Zone
Like many other dune pioneer zones in Africa Ipomoea pes-caprae is an important component but it is often not the principal species on West African coasts. In fact, two pioneer communities have been recognised. One dominated by Ipomoea pes-caprae and the other by Alternanthera maritima and Sporobolus virginicus. However, there is considerable local variation. The principal species associated with the Alternanthera maritima and Sporobolus virginicus zone are Fimbristylis obtusifolia, Sesuvium mesembrianthemoides and Stenotaphrum secundatum. Others include Canavalia datum, Eragrostis domingensis, Euphorbia glaucophylla, Ipomoea stolonifera, Panicum repens, Ramirea maritima, Schizachyrium pulchellum and Sporobolus robustus. With the exception of Fimbristylis obtusifolia and Sesuvium mesembrianthemoides most of the above species also occur in the Ipomoea pes-caprae community. Also included are species such as Cleome rutidsperma, Gisekia rubella, Merremia tridentate, Stylosanthes erecta, Tephrosia purpurea and Tricholaena monachne.

Main Strand Zone
A number of the pioneer species are also found here but with diminished density. The bulk of the vegetation has been described in terms of two vegetation types. In relatively little disturbed sites an association characterised by Canavalia rosea and Remirea maritime occurs. Other common associates include Diodia serratula and Schizachyrium pulchellum. The second is characterised by Eragrostis domingensis. Other species include Stylosanthes erecta and Tricholaena monachne.   The most striking appearance of this zone is its characteristically flattened appearance being largely composed of species having a prostrate or rosette habit. These are predominantly perennial herbs and grasses rather than shrubs.

Coastal Thicket
The strand vegetation eventually gives way to thicket but this can have a fairly heterogenous nature. Towards the strand exposure to salt-laden winds causes growth to be stunted whereas on lee slopes scrub can reach heights of of up to 4 m and include species that are not strictly coastal.  In Sierra Leone the principal shrubs are Chrysobalanus ellipticus, Chrysobalanus cularis, Dichrostachys glomerata, Parinari macrophylla and Phoenix reclinata and in the salt-trimmed seaward margin Dalbergia ecastaphyllum can be particularly prominent, whereas in Ghana Chrysobalanus orbicularis, Eugenia coronata, Phoenix reclinata and Sophora occidentalis are the principal species. On the Ivory Coast an association characterised by Ecastaphylletum brownie has been recognised which includes species such as Chrysobalanus ellipticus, Chrysobalanus orbicularis, Dalbergia ecastaphyllum, Diospyros tricolour, Hibiscus tiliaceus and Phoenix reclinata.  In the coastal thicket of Zaire two communities have been recognised. The first, described as a Chrysobalanus orbicularis-Dalbergia ecastaphylletum community, is similar to the Ecastaphylletum brownie association. Abutting the main strand zone it includes various salt-trimmed plants such as Annona glabra, Caesalpinia bonduc, Hyphaene guineensis, Phoenix reclinata, Ximenia Americana and Zehneria thwaistesii.  It usually forms a dense thicket between 1.5 and 9 m in height and normally includes many climbers and climbing shrubs. The second, which develops inland of the previous community, is described as a Hyphaene guineensis-Manilkara obovata community, and comprises many species common to the previous community. Here coastal species make up only about 10% of the overall composition. Some of the more typical associates include Bridelia scleroneura, Cassipourea barteri, Cola cabindensis, Deinbollia laurifolia, Ormocarpum verrucosum and Tarenna congensis.

Western Cape Strandveld

Occurring on the sands of marine origin on the coastal plain of Namaqualand, this veld type varies according to age, origin and depth of sand, and can be broadly divided into five subtypes: coastal zone strandveld, dunefield strandveld, tall strandveld and short strandveld. Coastal zone strandveld occurs in a belt just above high tide with a strong maritime influence. Cladoraphis cyperoides colonises the hummock dunes of this zone together with small shrubs such as Didelta carnosa and Tetragonia fruticosa. Other characteristic species are Amphibolia hutchinsonia and Salsola nallothensis. In slightly more stable areas the monotypic endemic Wooleya farinosa (Aizoaceae) can be found. Dunefield strandveld largely comprises a sparse community of mobile sand, but in the semi-mobile areas dense stands of Chrysanthemoides incana and Lebeckia multiflora may be present. Tall strandveld, reaching heights of 2 m or so, is the characteristic community of more stable dunes where there is deep sands.  Typical species are Eriocephalus africanus, Othonna cylindrica, Salvia lanceolata, Zygophyllum morgsana and the endemic Stoeberia utilis (Aizoaceae). Often tangled among this vegetation are the magnificent red blooms of Babiana thunbergii.  In sping there are brilliant displays of spring annuals, while in autumn colourful ammaryllids make their appearance. Short strandveld occurs where sand forms only a thin veneer possibly as a result of erosion. It reaches about knee-height and includes more succulent species than tall strandveld. In addition to the presence of a number of dwarf specimens of tall strandveld species there are also large blooms of Cephalophyllum spongiosum, Vanzijlia annulata, Zygophyllum cordifolium together with various crassulas, pelargonium and many vygie genera.

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