Brian John Huntley’s research while affiliated with Research Centre in Biodiversity and Genetic Resources and other places

The most vulnerable, yet biogeographically important forests of Angola are the relict patches of Afromontane forests of the highlands. This Chapter describes these ‘islands in the sky’ and their threatened endemic species. The small patches, totaling less than 10 km ² in area, lie from 2000–3000 km distant from their closest related forests in East, Southern and West Africa. The physical conditions, floristic and faunistic composition and biogeographic significance of the Afromontane forests and grasslands are described.

The climatic forces that determine Angola’s biodiversity and ecosystem patterns (and all life forms on Earth) are based on the energy that comes from the Sun. This chapter examines the concepts and functioning of solar radiation and photosynthesis, the basis of primary production. Strong seasonality of temperature and rainfall and their variation across latitude and altitude result in the diversity of Angola biomes, including Guineo-congolian lowland rain forest, Afromontane forest, mesic savanna, arid savanna, desert and mangrove biomes. Driving the climatic gradients are the oceanic and atmospheric systems, dominated in the north by the Intertropical Convergence Zone and in the south by the South Atlantic and Botswana Anticyclones. The physical processes driving these systems are described, and the local influences of maritime, continental, altitudinal and aspect factors that account for subtle changes from one ecoregion to the next are illustrated graphically and statistically. The recent impacts of El Niño events are described and the anticipated impacts of climate change on Angola are outlined.

The Angolan Escarpment is a physical feature that forms part of the Great Escarpment of Southern Africa. It comprises elements of all the major biomes of Angola. This chapter focuses on the biogeographical importance of the Escarpment Zone, which runs south from the Maiombe forests of Cabinda to the arid mountains rising above the Cunene River.

Tropical rain forests are represented in Angola by the narrow and fragmented southwards extension of the Guineo-Congolian rain forests of the Congo Basin and West Africa. This Chapter defines and characterises tropical rain forests, and compares the diversity of African forests with those of Central and South America and of South East Asia. The evolution and dynamics of African rain forests, and the role of human activity through the Holocene is discussed. Angola’s forest types are defined, their distribution, physical conditions, physiognomy and floristic and faunistic composition, plant-animal interactions, and forest gap-phase dynamics are detailed.

An introduction is presented to systems ecology, through models of the pathways, pools and fluxes of materials in terrestrial ecosystems, and the role of feedback mechanisms, and of the first and second laws of thermodynamics. Food chains, food webs and trophic levels provide structure to ecosystem processes. The importance of the C 4 photosynthetic pathway of the tropical grasses that dominate mesic and arid savanna biomes is emphasised. Details of the production, consumption and decomposition processes revealed in studies of mesic savanna in southern, central and western Africa illustrate the dynamics of carbon through terrestrial ecosystems. At landscape scale, the dynamics of the savanna/forest interface, that characterise much of northern Angola, is discussed in terms of tree-grass interactions and the existence of alternative stable states determined by fire.

This Chapter details the hierarchy of ecological assembly, from organismic, to population, to community, to ecosystem and to landscape levels. The processes of evolution by natural selection, genetic differentiation and speciation are described. Measures of species richness, evenness, diversity, endemism and categories of threat are important to conservation needs assessment and are illustrated with examples from Africa. The use of models of life history patterns (such as r- and K -strategies), and of the concepts of the ecological niche and guild are explained. Interactions between consumers and their food source provides a basis for their classification into herbivores, carnivores, omnivores and decomposers. To these are added interactions between two species with reciprocal effects—predation, parasitism, mutualism and commensalism. At landscape scales, interactions within and between populations and communities of existing and immigrant species, and the rates of immigration and extinction, are explored using the theories of island biogeography and of metapopulations. The impact of invasive species on rural livelihoods is used to demonstrate the fragility of natural communities to anthropogenic disturbance.

Part V synthesises the key messages included in this book—the fundamental elements of the evolution, structure and functioning of Angola’s terrestrial ecosystems, which in their diversity, represent a microcosm of African ecosystems. An incremental learning approach is followed in the book, presenting a strongly African perspective. From an introduction to the science of ecology, and an outline of the contemporary structure and composition of Angola’s biogeography, biomes and ecoregions, the narrative proceeds to detail on the geological and geomorphological history, soil genesis and properties, climatic drivers and gradients, and the role of disturbance by fire and herbivory in the evolutionary process. Basic ecological principles are then presented with examples from recent research in southern Africa. The six biomes represented in Angola are then described in detail. As an appendix, the book provides a comprehensive glossary of ecological terms.

This Chapter provides an introduction to basic elements of soil science, from an understanding of the soil profile, its develop and its importance to plant growth. The processes of weathering and the development of laterites, calcretes, salinised and other major soil types and their distribution in Angola are described. Soil water relations and soil chemistry and thus the availability of water and nutrients are fundamental determinants of plant growth, species composition and productivity. The differences between dystrophic (low base status) and eutrophic (high base status) soils and the distribution of the mesic/dystrophic savanna biome and the arid/eutrophic savanna biome, which dominate Angolan landscapes (totaling over 90% of the vegetation mantle of the country) are emphasised. The Key Soil Groups of Angola are mapped and their characteristics summarised. Sandy arenosols cover 53% of Angola, mainly comprising the Kalahari sands of the eastern half of Angola. Ferralsols cover 23% of Angola, occupying the spine of crystalline rocks along the western highlands. Both are of low nutrient status but carry dense miombo woodlands where they have not been transformed by human activities. Richer soils occur along the escarpment and hot coastal lowlands. The processes of land degradation, due to inappropriate soil management threaten the livelihoods of communities living on these fragile soils, are described.

The long history of Angola’s physical environment goes back to its Gondwanan origins, 550 million years ago. To give context to the present landscapes of Angola, a brief geological history of the Earth provides a backdrop to the dramatic evolutionary innovations that occurred in terrestrial ecosystems during the Miocene Epoch (23-5.3 million years ago), which shaped Africa’s savanna biomes as we know them today. The geomorphological patterns of Angola developed in response to periods of uplift (the Mayombe and Bié swells, the Angolan Escarpment), subsidence (the Congo and Kalahari Basins), erosion and deposition (the Planalto, Congo and Zambezian Peneplains). Angola has 12 main landscape groups, with which its ecoregions are closely aligned. The country is drained by six major transnational hydrological basins, providing the ‘water towers’ of southern and central Africa. The ecosystem services which these water resources provide to the region are described in terms of their role in pollution regulation, hydro-electric power generation and biodiversity maintenance.

The Savanna Biomes (Mesic/Dystrophic and Arid/Eutrophic) of Angola cover over 90% of the country. This Chapter presents the case for the recognition, across Africa, of these two distinctive savanna biomes, both defined by the co-dominance of fire-tolerant trees and C 4 grasses, falling within seasonal climates of warm, wet summers and mild, dry winters. The Mesic Savanna Biome occurs predominantly on the dystrophic (nutrient-poor) soils of the old peneplains of the Central African Plateau, mostly between 900 and 1400 m above sea level, and where rainfall ranges from 650 to 1400 mm per year. Fire is the main consumer of the grasslands, and is the key determinant of tree/grass dynamics. The biome covers 68% of Angola, and includes six ecoregions, to which may be added two ecoregions with a mosaic of tallgrass mesic savanna and forest patches occupying a further 16%, where Guineo-congolian forests and Zambezian mesic savannas interdigitate in northern Angola. Trees of the genera Brachystegia and Julbernardia characterise what is regionally know as miombo woodland. The physical, physiognomic, floristic and faunistic characteristics and unique natural phenomena of the biome are described in detail. The importance of the catena as a landscape feature determining vegetation pattern, and the role of termitaria in providing nutrient-rich islands in a sea of nutrient-poor soils, plus the abundance of ‘underground forests’ created by woody geoxyles, represent some of the special features of the biome.