Profiles of Angola’s Biomes and Ecoregions

Abstract

Each of Angola’s 6 biomes and 16 ecoregions is described and illustrated by habitat photographs to provide an introduction to their distribution, physiognomic structure and floristic and faunistic composition. The largest ecoregion (Angolan Wet Miombo Woodlands) covers 408,457 km², or 34.8% of the country, while the smallest (Afromontane Forest) covers less than 200 km² or 0.01% of Angola. Ecoregions are thus defined and mapped not on physical dimension but on their landscape and climatic characteristics, vegetation structure and floristic composition, and their land use potential.

Key Concepts and Questions: This Chapter Explains

• How the six African biomes represented in Angola are defined.

• Where the biomes are found, and what their landscape and climatic characteristics are.

• What the key physiognomic, floristic and faunistic features are of Angola’s 16 ecoregions.

Context: From African Biomes to Angolan Ecoregions

The introductory outlines of Angola’s biomes, mosaics and ecoregions presented here form a continuum from the synopses of African biomes and mosaics given in Sect. 2.3, and elaborated in detail in Part IV of this book. Brief outlines of Angola’s biomes, mosaics and ecoregions set the stage against which the ecological drivers of such ecosystem diversity are analysed in Part ll. In the ecoregional profiles, reference is made to the WWF Ecoregion numbers (https://ecoregions2017.appspot.com) and the vegetation units in Barbosa (1970), where additional detail might be found.

1 Guineo-Congolian Rain Forest Biome and Forest/Savanna Mosaic

Across northern Angola, the rich Guineo-Congolian flora of African rain forests is represented in the moist forests found along the low mountains and escarpments of Cabinda, Zaire, Uíge, Cuanza-Norte, Cuanza-Sul and Malange. The flora penetrates southwards along the Angolan escarpment as isolated fragments in Benguela and Huíla provinces and as gallery forests up the tributaries of the Congo drainage in Malange and Lunda-Norte. Biogeographically important but poorly studied forests also occur along the Quela and Tala Mungongo escarpments on the western margin of the Baixa de Cassange. These fire-sensitive forests form a mosaic within fire-tolerant Western and Southern Congolian tall grasslands and savannas as the vegetation transitions into the Zambezian flora of the Mesic Savanna Biome. The Guineo-Congolian Rain Forest Biome (sensu strictu) occupies less than 1% of Angola. Far more extensive are the tallgrass savannas of the Congolian Rain Forest/Mesic Savanna Mosaic, that forms a transition between the Guineo-Congolian Rain Forest Biome and the Mesic Savanna Biome. These transitional mosaics (Ecoregions 2 & 3) cover 16% of Angola.

The Maiombe forests are of great importance for the conservation of large mammals, especially for Western Lowland Gorilla, Central Chimpanzee, Forest Elephant and Forest Buffalo. The Maiombe forests are of high conservation priority as home to 14 species of primate, five species of forest duiker and the enigmatic Water Chevrotain.

Ecoregion 1. Guineo-Congolian Rain Forest (WWF 5; Barbosa 1, 2, 3; Figs. 3.1 and 3.3). Angola has a rather limited area of closed canopy tropical rain forest (ca. 3500 km²). These forests occur mostly in Cabinda, where a continuation of the narrow belt of Lower Guinean evergreen to semi-evergreen broadleaf forest extends from central Cameroon to just north of the mouth of the Congo River. Outliers of Guineo-Congolian Rain Forest floristic and faunistic elements follow the Angolan Escarpment in isolated blocks in Cuanza-Sul, and as tiny forest fragments in the seaward-facing ravines of the Serra da Chela. The inland hills of Cabinda form the drier southern limit of the Mayombe forest block, known in Angola as the Maiombe forest. Most of the ecoregion lies on Precambrian rocks, producing cambisols and nitisols. The Alto Maiombe forests of Cabinda receive from 1200 to 1600 mm of rain per annum, with dry spells in July–September and again in January. The canopy of mature forest in Maiombe may reach 60 m height, but generally the canopy is between 30 and 40 m height. Important genera include Gilbertiodendron, Julbernardia, and Tetraberlinia in climax forest and Milicia, Musanga, Piptadeniastrum, Ricinodendron and Terminalia in disturbed, secondary forest. The semi-deciduous forests of Zaire, Uíge, Cuanza-Norte (including the large Dembos forest block) and Cuanza-Sul are drier, with from 800 to 1400 mm rainfall per annum. As a whole, the ecoregion has, in African terms, exceptional species richness with many endemic species.

Fig. 3.1

Subsistence farm in Alto Maiombe Forest, Cabinda. Tall trees include forest margin pioneers Terminalia superba with erect white trunks, and the branched crowns of Musanga cecropioides at left and right of the scene

Ecoregions 2 & 3. Western and Southern Congolian Forest/Savanna Mosaics (WWF 63, 58; Barbosa 7–10, 12–14, 26; Figs. 3.2, 3.4 and 3.5). These two large blocks (136,000 and 54,000 km² in Angola) of mixed forest and tallgrass savannas extend the reach of rain forests as gallery forests in valleys and isolated forest fragments on hillsides and plateaus, southwards from the Congo Basin. Rainfall ranges from 1000 to 1600 mm per annum, with a distinct dry season from May to September. The Guineo-Congolian Rain Forests comprise less than 5% of the landscape of these mosaics, but contribute possibly as much as 80% of the species diversity of these two ecoregions. The major portion (ca. 95%) of these two ecoregions consists of tallgrass savannas which belong, floristically, to the Mesic Savanna Biome. They are therefore mapped as transitional mosaics in Figs. 2.2 and 2.4. Tall grasslands with sparse trees characterise the sandy plateaus between river valleys. Extensive areas of Ecoregion 3, for instance, are treeless grasslands with an abundance of geoxyles (Box 14.3) and are known in Lunda-Norte as the chanas da borracha due to the abundance of the rubber plant, Landolphia parvifolia.

Fig. 3.2

Western Congolian Forest/Savanna Mosaic near Camabatela, Cuanza-Norte. Tall grasses of Hyparrhenia and Trachypogon species, with a fire-tolerant Hymenocardia acida in left foreground

Fig. 3.3

Location of Ecoregions: 1 Guineo-Congolian Rain Forest

Fig. 3.4

Location of Ecoregions: 2 Western Congolian Forest/Savanna Mosaic

Fig. 3.5

Location of Ecoregions: 3 Southern Congolian Forest/Savanna Mosaic

The landscapes of northern Angola range from 1000 to 1500 m in the mountainous regions of Zaire and Uíge, and the high plateau of Malange and the plains of Lunda-Norte. The landscapes descend via a series of valleys to 500 m in the Congo Basin along the Cuango River, and down to sea level at the mouth of the Congo. Soils include ferralsols on Precambrian crystalline rocks in the west, and arenosols of the Kalahari sands in the east. The deeply incised valleys occupied by gallery forest usually lie on exposed Karoo strata and Precambrian rocks.

This very mixed topography carries a rich flora and fauna, where elements of Zambezian and Guineo-Congolian phytogeographic regions meet, and where the fauna of Guineo-Congolian forests interdigitate with those of the Zambezian woodlands, savannas and grasslands of the south and east. Trees of genera such as Dialium, Daniellia, Cryptosepalum and Marquesia are prominent in woodlands and dry forests of the northeast of Angola. Typical miombo genera such as Brachystegia, Julbernardia, Burkea and Isoberlinia increase in importance from north to south, but never dominate. The river valleys have tall gallery forests in which species of Ceiba, Entandrophragma, Milicia, Musanga, Piptadeniastrum, Raphia and Xylopia are found. The grasslands here comprise tall, dense Andropogon, Hyparrhenia, Loudetia and Trachypogon species, reaching 4 m height, which rapidly develop a high biomass of fuel between frequent, hot fires. The sharp boundary between forest and grassland marks the limit of fire penetration. Indeed, few tree species can survive the regular fires that sweep across these tall grasslands, and those that do survive are well adapted to resprouting. Fire-tolerant woody genera include Annona, Erythrophleum, Hymenocardia, Piliostigma and Strychnos.

2 Afromontane Forest and Grassland Biome

Angola’s most isolated and vulnerable biome comprises two ecoregions. The highest areas of the Angolan plateau and mountains have relatively small areas of Montane Grassland on the Huambo, Huíla, Benguela and Bié highlands, with very small remnants of Afromontane flora in the forests and shrublands along the Marginal Mountain Chain—specifically Mount Moco, Mount Namba and along the Chela Escarpment. They are important centres of biotic richness and endemism, although occupying only 1.1% of the country. Most larger mammals of the biome have been exterminated. The increasing pressures of land transformation for agriculture place the rich avifauna of forest and grassland habitats at risk of local extinction. The avifauna is notable for high levels of endemism and of narrow-range species.

Ecoregion 4. Afromontane Forests (WWF 77, Barbosa 5, 6; Figs. 3.6, 3.7 and 3.8). The Afromontane Forests of Angola are the most fragmented and isolated of all representatives of the Afromontane Biome in Africa. With a total area of less than 1000 ha across their entire range in Angola, they occur as small forest patches that are provided some shelter from fire in deep valleys and by rock outcrops. These highland sites receive from 800 to 1600 mm rainfall per annum, with a dry season from June to September. The shallow soils lie on Basement Complex and West Congo crystalline rocks. The weakly stratified forests have a broken canopy of up to 20 m height. Trees include Afromontane genera such as Apodytes, Cassipourea, Erythroxylum, Halleria, Ilex, Maesa, Myrica, Nuxia, Pittosporum and Podocarpus. The importance of these forests lies in the rich endemic and near-endemic bird species that occur as isolated, disjunct populations, over 2000 km from related species and subspecies elsewhere in the Afromontane forests of eastern, southern and western Africa.

Fig. 3.6

The largest block of forest on Mount Moco, at 2200–2450 m, photographed in 1972. Note the short montane grasslands and shrublands of Philippia and Protea

Fig. 3.7

Protea welwitschii in the grasslands of Mount Moco. Described as the tallest protea in the world in 1960. Photo J. S. Beard. The proteas of tropical Africa. Kangaroo Press

Fig. 3.8

Location of Ecoregions: Black dots: 4 Afromontane Forest

Ecoregion 5. Montane Grasslands (WWF 77, Barbosa 32; Figs. 3.7, 3.9 and 3.10). The Montane Grasslands of the Angolan Marginal Mountain Chain and Ancient Plateau (Diniz, 2006), extend across the highlands of Cuanza-Sul, Benguela, Huambo, Bié and Huíla. These grasslands await a detailed study of their botanical and faunistic diversity. Lying mostly at from 1500 to 1800 m, the rolling hills rise to 2620 m on Mount Moco, the highest point in Angola. The underlying geology comprises crystalline rocks producing shallow leptosols, ferralsols and grading into arenosols in the east. These short grasslands cover approximately 1% of Angola. They are important contributors to the ‘water towers’ of central and southern Africa, feeding the Cuanza, Cubango, Cunene and upper tributaries of the Congo and Zambezi. The seasonally waterlogged soils result in the near absence of trees but an abundance of grass, forb and geophyte species, including many orchids. Better-drained areas have shrubs and low trees, often with the appearance of ‘dwarf’ miombo (2–5 m height) of Brachystegia spiciformis, B. floribunda and Julbernardia paniculata especially on shallow rocky soils over quartzites. Seasonally waterlogged sites have extensive areas dominated by ‘underground forests’ of geoxyles, locally known as anharas do ongote (Box 14.3).

Fig. 3.9

Location of Ecoregions: Grey shading: 5 Montane Grasslands

Fig. 3.10

Moist Montane short grassland at 2000 m, Humpata, Huíla

3 Mesic Savanna Biome

Two savanna biomes are recognised in Africa, the Mesic/Dystrophic and the Arid/Eutrophic savannas, as outlined in Chap. 2 and detailed in Chaps. 14 and 15. Both savanna biomes comprise floras belonging to the most extensive regional centres of endemism in Africa, the Sudanian Centre (north of the Equator) and the Zambezian centre (mostly south of the Equator). The Zambezian flora dominates Angola, occupying over 90% of the country. The Mesic Savanna Biome, typical of the Zambezian centre of endemism, extends over 68% of Angola, predominantly on the interior plateau, above 1000 m, and on freely draining nutrient-poor and acidic (dystrophic) soils. Fire is the key driving force that maintains the mix of grasses and trees that constitute the woodlands, savannas, shrublands and grasslands of the biome. Fire prevents the transformation of savanna to closed-canopy forest even where mean annual rainfall is sufficient to support closed rain forest.

Characteristic of central Africa’s mesic savannas are the miombo woodlands (known as mato de panda in Angola, based on the local name mupanda or m’panda for Brachystegia spiciformis). Miombo trees are distinctive in their shape, usually with relatively short, slender trunks with ascending branches forming a light, shallow and often flat crown. The mesic savannas occupy distinct landscapes. To the west of the central planalto and the Marginal Mountain Chain, the Angolan Escarpment Woodlands form a transition between the highlands and coastal lowlands, following the rolling hills and steep slopes of the Central Escarpment. The most extensive of Angola’s 16 ecoregions is the Angolan Wet Miombo that covers the central Angolan plateau. To the southeast of the Wet Miombo is the Dry Miombo beyond which lie the Zambezian Baikiaea Woodlands. A small area of the Central Zambezian Wet Miombo falls within eastern Moxico. Within the geographic embrace of miombo woodlands are two further ecoregions, recognised by Burgess et al. (2004) as falling within distinctive biomes (Flooded Grasslands and Dry Broadleaf Forests), but are treated here as ecoregions within the Mesic Savanna Biome. The vast plains of the Cameia/Bulozi catchment are dominated by Zambezian Flooded Grassland. Dry Broadleaf Forest is represented in Angola by a small extension of the Zambezian Evergreen Dry Forest in eastern Moxico. Collectively, these ecoregions constitute the Mesic Savanna Biome.

The grasslands and open woodlands of the Mesic Savanna Biome originally carried a diverse vertebrate fauna. Large mammal species (now decimated) which had their main distribution in the biome include Lichtenstein’s Hartebeest, Roan Antelope, Giant Sable Antelope, Defassa Waterbuck and Puku. Bird species typical of the miombo habitat include Miombo Wren Warbler, Miombo Tit and Miombo Scrub Robin.

Ecoregion 6. Angolan Escarpment Savannas (WWF 35; Barbosa 18B, 22; Figs. 3.11, 3.14 and 3.15). South of the Cuanza River and along Angola’s Central Escarpment, this narrow band of mixed savannas lies between the arid savannas of the coastal lowlands (Ecoregions 12, 13 and 14) and miombo savannas of the planalto (Ecoregion 7). This mosaic of tall grasslands and woodlands constitutes Angolan Escarpment Savannas which include Barbosa (1970) vegetation types 18B and 22. Barbosa’s vegetation type 18B comprises fire-tolerant tall grass (1–3 m height) and short miombo (4–6 m height). Trees include Brachystegia spiciformis, B. wangermeeana, B. boehmii, B. gossweileri, Burkea africana, Combretum collinum, Cussonia angolensis, Pterocarpus angolensis, Terminalia sericea and Uapaca benguelensis. Grasses are mostly Andropogoneae. Vegetation type 22 lies below Type 18B, on the lower and drier slopes of the Escarpment and above the coastal plain. Outliers of Guineo-Congolian Forest patches and thickets occur in moist valleys and ravines. Fire-tolerant short trees are scattered within an open savanna of tall grasses. The abundant yellow flowers of Cochlospermum angolense makes this tree the most conspicuous characteristic of this vegetation type, together with Acacia sieberiana, Adansonia digitata, Albizia versicola, Burkea africana, Cussonia angolensis, Piliostigma thonningii, Pterocarpus rotundifolius, Sterculia quinqueloba and Terminalia sericea. Grasses are mainly members of the Andropogoneae (Figs. 3.12, 3.13).

Fig. 3.11

Grey shading: Location of Ecoregions: 6 Angolan Escarpment Savannas

Ecoregion 7. Angolan Wet Miombo Woodlands (WWF 36, 39; Barbosa 16, 17, 18A; Figs. 3.12, 3.16 and 3.17). These woodlands, savannas and grasslands typically receive more than 1000 mm rainfall per year and lie at elevations between 900 and 1500 m. The deep, moist soils support a canopy height of 15–25 m. Brachystegia spiciformis (mupanda) occurs in varying densities and robustness throughout the miombo biome, with other species (B. floribunda, B. glaberrima, B. longifolia, B. wangermeeana, B. gossweilerii) at varying densities according to soil characteristics. Julbernardia paniculata (mumue) is also widespread across the Angolan miombo, together with Burkea, Cryptosepalum, Guibourtia, and Pterocarpus. The wet miombo is a mosaic of woodlands, savannas and grasslands, with a more or less continuous grass cover, always of C₄ grasses, even under a thin cover of the woodland canopy, where the grass biomass might be too sparse to support fire penetration in most seasons. Shrubs and short trees of this miombo include Diplorhynchus condylocarpon, Baphia massaiensis and Copaifera baumiana. On the edges of drainage-line grasslands (mulolas, dambos) species of Monotes, Protea and Uapaca occur as short trees. Grasses include species of Andropogon, Digitaria, Elionurus, Eragrostis, Hyparrhenia, Loudetia, Monocymbium, Setaria and with Panicum becoming prominent under woodland.

Fig. 3.12

Grey shading: Location of Ecoregions: 7 Angolan Wet Miombo

Ecoregion 8. Angolan Dry Miombo Woodlands (WWF 42; Barbosa 24; Figs. 3.13 and 3.18). These woodlands occur on the deep, heavily leached Kalahari sands of southeast Angola, where the gently undulating landscape with broad valleys is drained by the crystal-clear waters of the Longa, Cuito and Cuando basins, descending from 1200 to 1000 m. The deciduous woodland canopies are from 8 to 15 m in height. The floral composition is less rich than the Wet Miombo, with Brachystegia bakerana and Burkea africana prominent, along with Julbernardia paniculata, Guibourtia coleosperma, Dialium engleranum, Schinziophyton rautenenii and Cryptosepalum exfoliatum. The catenal series of broad valleys (mulolas) between the rises (ancient dunes) are seasonally waterlogged and carry grasslands of Loudetia, Trachypogon, Eragrostis and Monocymbium. On the open margins of the catenas, communities of 'underground trees' (geoxyles) are found and include Brachystegia russelliae, B. bakerana, Parinari capense and Chamaeclitandra henriquesiana.

Fig. 3.13

Grey shading: Location of Ecoregions: 8 Angola Dry Miombo

Fig. 3.14

Fire-tolerant Cochlospermum angolense trees typical of the tall grasslands covering the rolling the hills of the Angolan Escarpment Savannas

Fig. 3.15

Flower of Cochlospermum angolense Photo Ernst van Jaarsveld

Fig. 3.16

Miombo in the Quibala hills, Cuanza-Sul. Photo Antonio Martins

Fig. 3.17

Angolan Wet Miombo Woodland dominated by Brachystegia species in Luando Strict Nature Reserve, Malange. African Wild Dogs resting on the road

Fig. 3.18

Miombo woodland with dense grass and forb ground cover. North of Cuvango, Huíla Province. Photo Antonio Martins

Ecoregion 9. Zambezian Baikiaea Woodlands (WWF 64; Barbosa 15, 25; Figs. 3.19, 3.22 and 3.23). These woodlands occur at from 1000 to 1300 m, on the leached and nutrient poor Kalahari sands which cover most of the gently undulating landscapes of southeast Angola. Annual rainfall in the Angolan distribution of this central African woodland is 600–750 mm, strongly seasonal, with up to eight dry months. Despite the low rainfall, the deeply rooted Baikiaea plurijuga trees (muiumba or mucusse) can form woodlands of up to 20 m height, usually on the crests of ancient dune fields. While Baikiaea is recognised as the indicator species of this ecoregion, it nowhere dominates the canopy nor the biomass. A mosaic of woodland, thicket, savanna and grassland species characterise the ecoregion. Tree genera include Afzelia, Baikiaea, Burkea, Dialium, Erythrophleum, Guibourtia, Schinziophyton and Terminalia in the woodlands, with dense thornless thickets of coppicing species of Baphia, Bauhinia, Combretum, Croton, Pteleopsis, Pterocarpus and Strychnos on areas with shallow sands overlying water-impermeable duricrusts. The transition from typical miombo to Baikiaea woodlands is at ca. 700 mm annual precipitation (Figs. 3.20, 3.21).

Fig. 3.19

Location of Ecoregions: 9 Zambezian Baikiaea Woodlands

Fig. 3.20

Location of Ecoregions: 10 Zambezian Evergreen Dry Forest

Fig. 3.21

Location of Ecoregions: 11 Zambezian Flooded Grasslands

Fig. 3.22

Baikiaea woodland in Bicuar National Park

Fig. 3.23

Guibourtia community within Baikiaea woodland in southern Cuando Cubango. Both woodlands are on deep Kalahari sand

Ecoregion 10. Zambezian Evergreen Dry Forest (WWF 33; Barbosa 4; Figs. 3.20, 3.24 and 3.25). This evergreen forest type occurs as small patches within miombo communities over a broad area of eastern Angola (Lunda-Norte, Lunda-Sul, Bié, Cuando Cubango), reaching its greatest extent in the south-eastern border of Moxico with Zambia. This dry forest is best developed where it occurs on deep well-drained Kalahari arenosols with an adequate supply of water in their deeper soils during the dry season. This ecoregion lies at 1100–1200 m. Floristically, Zambezian elements dominate, with some Guineo-Congolian and Afromontane species. The evergreen leguminous tree Cryptosepalum exfoliatum dominates, together with Brachystegia spiciformis, Daniellia alsteeniana, Entandrophragma delevoyi, Guibourtia coleosperma, Erythrophleum africanum, Ochna pulchra, Marquesia acuminata, M. macroura and Pteleopsis anisoptera.

Fig. 3.24

Cryptosepalum/Marquesia Dry Forest on deep Kalahari sands, Lunda-Norte

Fig. 3.25

The extensive plains known as chanas da borracha of Lunda-Norte, with sparse grass cover but abundant geoxyles appearing following fire

While Cryptosepalum reaches up to 25 m in height, most of the forest communities are shorter, at 10–15 m. Due to the typically closed canopy the herbaceous layer is sparse and often carries a bed of mosses and liverworts. Lianas and epiphytes, usually uncommon in miombo woodlands, are frequent. Epiphytic pteridophytes of the genera Polypodium, Platycerium and Lycopodium are abundant in these forests. Cryptosepalum exfoliatum is fire-intolerant, although the dense tree canopy, shaded microclimate and sparse forest ground cover normally prevents the entry of fires. However, if subjected to frequent fires, or to shifting cultivation, the forest converts to an open, ‘derived’ savanna known as tchirhuto in Lunda-Norte and chipya in Zambia. This stunted savanna/thicket includes most of the fire-tolerant miombo species plus Aframomum biauriculatum, Pteridium aquilinum and climbers such as Smilax kraussiana. It is the least well-studied ecoregion of Angola.

Ecoregion 11. Zambezian Flooded Grasslands (WWF 76; Barbosa 31; Figs. 3.21, 3.26, 3.27, 3.28 and 3.29). The major sources of the waters of the Zambezi River lie in the ‘water towers’ of the Angolan plateau. A key catchment flows via the Bulozi Floodplain, perhaps the largest ephemeral wetland in Africa (Mendelsohn & Weber, 2015). Half of the floodplain is found in Moxico, the rest in neighbouring Zambia. This vast system of seasonal wetlands, grasslands and fringing miombo savannas and woodlands, and narrow gallery forests, has received very little attention from researchers, despite the teeming game populations that occurred in Cameia National Park during colonial times. Barbosa (1970) devotes less than one page to its vegetation. The floodplains lie at 1000–1100 m, and stretch over 800 km from north to south and 200 km west to east at their widest points. They cover Kalahari sands, with seasonally waterlogged gleysol clays, often with hardpan layers beneath the surface, making tree growth impossible over much of the area. Fires sweep across the dry grasslands almost every year, further suppressing woody plant growth, other than of the ‘underground trees’—the geoxyles. The raised surfaces of termite mounds and fossil sand dunes provide a less challenging substrate for typical miombo trees and shrubs. The grasslands carry a diversity of grass species, dominated by Loudetia simplex, along with species of Acroceras, Arundinella, Bothriochloa, Chloris, Cynodon, Echinochloa, Imperata, Leersia, Oryza, Setaria, Tristachya, Vetiveria and Vossia.

Fig. 3.26

Floodplain of the Luele River, Lunda-Norte

Fig. 3.27

Lechwe on an old termitarium, Luando floodplain, Luando Strict Nature Reserve, Malange

Fig. 3.28

Aerial view across the Bulozi Floodplain. Photo John Mendelsohn

Fig. 3.29

Marginal woodland and floodplain grassland, Bulozi Floodplain, Moxico. Photo John Mendelsohn

4 Arid Savanna Biome

The arid savannas of Angola cover 12.9% of the country and are characterised by low rainfall (less than 650 mm per annum) and richer (eutrophic) soils than the leached, nutrient-poor (dystrophic) ferralsols and arenosols of mesic savannas. The arid savannas of southwestern Africa include large areas of typically dystrophic Kalahari sand, south of Angola, where they are ephemerally eutrophic when pulses of nutrients are released during rainfall events. The arid savannas typically lie below 1000 m, while the mesic savannas generally lie above 1000 m. In the southwest of Angola, Mopane Woodland occupies richer soils at the base of the Chela Escarpment and along the Cunene River. Here the Zambezian flora mixes with representatives of the Karoo-Namib flora within the Namib Savanna Woodland ecoregion that extends northwards along the coast towards Benguela. This arid coastal climate continues under the influence of the Benguela Current as a mosaic of grasslands, savannas, thickets and dry forests as the Coastal Arid Savanna ecoregion to beyond the Congo River, and as a narrow coastal margin in Cabinda.

The arid savannas of Africa typically support high biomasses of herbivores, mostly herding grazers and mixed feeders. In earlier times, large populations of many arid savanna mammal species were recorded in the south and southwest of Angola, especially Common Wildebeest, Cape Buffalo, Common Eland, Greater Kudu, Plains Zebra, Black Rhino and Savanna Elephant. Bird species typical of the biome include White-tailed Shrike, Monteiro’s Hornbill, Benguela Long-tailed Starling and Pririt Batis.

Ecoregion 12. Angolan Mopane Woodlands (WWF 34, Barbosa 20, 21; Figs. 3.30 and 3.33). The leguminous tree Colophospermum mopane (mutiati) occupies much of the lower Cunene valley forming woodlands, savannas and shrublands. Mostly confined to the hot dry valleys of the main drainage basins of southern Africa (Cunene, Zambezi, Luangwa, Limpopo) the species is typically found on heavy clay soils and stony hills in arid savannas receiving less than 650 mm rainfall per annum. Although often found as a single dominant species in woodlands, it also forms mixed communities with species of Acacia, Adansonia, Albizia, Boscia, Combretum, Commiphora, Sclerocarya and Terminalia. Together with grasses of the genera Anthephora, Aristida, Cenchrus, Eragrostis and Enneapogon, it provides rich herbage for mammal browsers, grazers and mixed feeders (Figs. 3.31 and 3.32).

Fig. 3.30

Location of Ecoregions: 12 Angolan Mopane Woodlands

Ecoregion 13. Namib Savanna Woodlands (WWF 104; Barbosa 27; Figs. 3.31 and 3.34). This ecoregion occupies a narrow belt of coastal lowlands from the Cunene River northwards to Sumbe, wedged between the Angolan Namib Desert and Angolan Mopane Woodland ecoregions. The region has a mix of rolling stony hills and sandy plains, between sea level and 500 m. Rainfall increases from south to north, from 100 to 400 mm. Short trees and shrubs of the genera Acacia, Balanites, Boscia, Catophractes, Combretum, Maerua, Rhigosum, Sterculia and Terminalia form open savanna, with extensive grasslands of Aristida, Cenchrus, Enneapogon, Schmidtia, Stipagrostis, Tricholaena and Urochloa species. Succulent herbs, shrubs and trees are common.

Fig. 3.31

Location of Ecoregions: 13 Namib Savanna Woodlands

Ecoregion 14. Coastal Arid Savannas (WWF 35; Barbosa 3, 7, 10, 11 and 23; Figs. 3.32, 3.35 and 3.36). The arid coastal belt from Sumbe northwards to the Congo River comprises marine sediments of sands, marls and limestone, lying from sea-level to 500 m. The influence of the Benguela Current accounts for the low rainfall, mainly below 500 mm per year, across the ecoregion, as explained in Chap. 5. A limited group of tree species, including Acacia welwitschii, Adansonia digitata, Euphorbia conspicua and Sterculia setigera, plus grasses of the genera Eragrostis, Digitaria, Heteropogon, Schizachyrium and Setaria characterise the ecoregion’s flora. The vegetation is nevertheless very diverse, including extensive monospecific grasslands of Setaria welwitschii, open mixed clump savannas, dense low thickets, mixed woodlands, dry forests and gallery forests. The dry deciduous forests of ravines and narrow valleys that skirt the first step of the escarpment have a mix of Zambezian and Guineo-Congolian tree species, forming a closed canopy with little if any understorey strata.

Fig. 3.32

Location of Ecoregions: 14 Coastal Arid Savannas

Fig. 3.33

Mopane Colophospermum mopane woodland in Mupa National Park. Photo Francisco Maiato Gonçalves

Fig. 3.34

Mixed commiphora and acacia savanna at the interface between the Namib Savanna Woodlands and Angolan Namib Desert ecoregions, Iona National Park, Namibe. Photo Ernst van Jaarsveld

Fig. 3.35

Tall mono-specific Setaria welwitschii grasslands on the deep vertic clays of Quiçama inland of Cabo de São Braz

Fig. 3.36

Clump savanna of Adansonia digitata and Euphorbia conspicua with Schizachyrium sanguineum, Heteropogon contortus and Digitaria milanjiana grassland, on the sand plateau of Quiçama

5 Namib Desert Biome

A narrow tongue of hyper-arid desert stretches from the Cunene River to the Carunjamba River near Lucira, with a mix of Karoo-Namib and Zambezian floristic elements. Vegetation-less dunes occur along the coast, with gravel plains occupied by dwarf shrublands to the interior, succeeded by ephemeral grasslands on the sandy plains of intermontane basins. The rocky hills to the east have mixed open woodlands and a light cover of grasslands. This biome occupies ca. 0.4% of the country. Despite the challenges of the desert environment, a diverse and specialised fauna (Chap. 11) is to be found in Iona National Park, today under severe human-mediated threat.

Mammals found in the biome include Cape Fox, Meerkat, Aardwolf, Springbok, Kirk’s Dik-dik, Gemsbok and Hartmann’s Mountain Zebra. Bird species typical of the desert include Ostrich, Ruppell’s Korhaan, Ludwig’s Korhaan and Burchell’s Courser.

Ecoregion 15. Angolan Namib Desert (WWF 98; Barbosa 28 and 29; Figs. 3.37, 3.38 and 3.39). The Angolan sector of the Namib Desert extends from the Cunene River to the Carunjamba River, forming a narrow (20–80 km) wedge between the Atlantic Ocean and the coastal plains which skirt the Angolan Escarpment. Characterised as a hyper-arid desert, the ecoregion receives less than 150 mm rainfall per annum, with much of the area receiving half of this figure. Mobile dunes and hard calcrete, gypsum and gravel plains lie between the sea and intermittent sandy plains and rocky hills of the interior. The dunes have little if any vegetation. Inland, succulent shrubs, thorny bushes and low trees of Acacia, Commiphora, Euphorbia, Rhigozum, Sesamothamnus and Sterculia are scattered across a matrix of sparse, short grasses of Stipagrostis species. Over much of the desert, the iconic gymnosperm Welwitschia mirabilis is common. Despite its aridity, the desert is home to a rich diversity of vertebrate and invertebrate species, these demonstrating complex adaptations to life in an almost waterless environment.

Fig. 3.37

Location of Ecoregion 15. Angolan Namib Desert

Fig. 3.38

Welwitschia mirabilis on a gravel plain with dead annual grasses and herbs

Fig. 3.39

Euphorbia and Commiphora at the base of a gneiss outcrop, with sparse arid grasslands during an extended dry period. Iona National Park

6 Mangrove Biome

The mangrove communities of Africa are given biome status by Burgess et al. (2004), as part of the global network of tropical mangroves. The limited area occupied by mangroves and the challenges of the environment account for the very low vertebrate diversity found in the biome, which however includes three crocodile species in Cabinda—West African Slender-snouted Crocodile, African Dwarf Crocodile and Nile Crocodile.

Ecoregion 16. Central African Mangroves (WWF 111; Barbosa 14A; Figs. 3.40, 3.41 and 3.42). At the mouths of the Congo, Cuanza, Longa and Cuvo rivers, small communities of Central African Mangroves are found. The mangroves form tall (20 m height) forests of Rhizophora species along the margins of the major river estuaries, flanked by shorter mangrove communities on mudbanks that occur in embayments and lagoons, where species of Avicennia form dense short woodlands. In terms of their flowering plant diversity, mangroves are extremely species poor, with only four mangrove tree species and two seagrass species recorded in the ecoregion. The marine fauna of the ecoregion is rich, as is the avifauna that uses the sandbanks and mudflats of the estuaries and embayments of the ecoregion.

Fig. 3.40

Location of Ecoregion 16: Central African Mangroves. Arrows indicate location of Mangrove communities at mouths of rivers

Fig. 3.41

Mangroves at the mouth of the Congo River, Zaire Province. Photo Kellie Pendoley

Fig. 3.42

Mangroves at the mouth of the Congo River, Zaire Province. Photo Kellie Pendoley

7 Angolan Escarpment Zone

Inland of the coastal plain and following the Angolan Escarpment between northern Cabinda and the Cunene River is a complex mix of biome elements, vegetation structure and floristic affinities (Zambezian, Guineo-Congolian and Afromontane). The Angolan Escarpment Zone (AEZ) constitutes a physiographic Zone rather than a biogeographic unit. It comprises a mosaic of grasslands, savannas, woodlands, thickets and forests. The Zone includes many endemic plant and animal species that have evolved along the steep gradients of its landscapes. On the Maiombe and Northern Escarpments, Guineo-Congolian Rain Forests (Ecoregion 1) and tallgrass savannas of the Western Congolian Forest/Savanna Mosaic (Ecoregion 2) dominate, while the Angolan Escarpment Savannas (Ecoregion 6, below) occur along the Central Escarpment, comprising mixed grasslands and woodlands of Mesic Savanna elements. The biogeographical and ecological importance of the Angolan Escarpment is discussed in detail in Chap. 18.