Key Concepts and Questions: This Chapter Will Explain

  • How Angola’s landscapes were developed over the 550 million years since the formation of Gondwana.

  • What dramatic climatic changes and evolutionary innovations led to the development of the African savannas and their abundant wildlife.

  • How climate, soils, fire and herbivory shape Angola’s biomes and ecoregions.

  • What unifying ecological concepts explain how ecosystems are structured and how they function.

  • Why ecology is an important and exciting career.

Context: Angola as a Microcosm of Africa’s Ecological Diversity

The aim of this volume is to provide Angolan students with an introduction to terrestrial ecology, presenting strongly African, and specifically Angolan, perspectives. In reading the chapters, it soon becomes apparent is that Angola is a microcosm of Africa, with an unparalleled diversity of biomes and ecoregions, from rain forest to desert in one country. This richness obliges the Angolan student to become familiar with a much broader and more complex suite of concepts, phenomena and technical terms than is the case for students of less biodiverse countries.

This concluding chapter provides a synopsis of key elements of Angola’s ecological structure and functioning, highlighting features and concepts that emerge in individual chapters. These elements provide the student with a toolkit of fundamental concepts and processes that will guide an understanding of Angola’s terrestrial ecosystems.

Four themes or ‘leitmotifs’ recur throughout this book and underpin its didactic objectives:

  • Ecology is about recognizing patterns and processes that operate at widely differing scales of time and space.

  • Ecology is about the unique mechanisms of survival, growth and reproductive output of organisms in relation to their environment.

  • Ecology does not make sense except in the light of evolution. But equally, very little in evolution makes sense except in the light of ecology.

  • The whole is greater than the sum of its parts. Interactions and webs of interdependencies between individuals, species and populations and their environments create collective, emergent properties that shape ecosystem structure and function.

1 The Big Picture: Global Tectonic and Climatic Forces that Have Shaped Angola’s Biomes and Biota

A long-term perspective of global geological and climatic dynamics provides an essential backdrop against which to understand African and Angolan landscapes and biota. These developed across hundreds of millions, indeed billions of years, through processes of change that continue to this day. Presenting the ‘big picture’ of Angola’s history must therefore refer to the dramatic forces (tectonic, oceanic, atmospheric) that have shaped life on Earth.

The Gondwanan Origins of Angola

Since Earth’s origin 4.5 billion years ago, tectonic events across the Earth’s crust resulted in the creation of supercontinents, such as Laurasia and Gondwana. Gondwana formed 550 Ma and started to break up from 180 Ma, finally splitting off the southern continents (South America, Antarctica, Africa, Australia) by 130 Ma. With the separation of the southern continents, the vast oceans of the southern hemisphere were formed. Over land and sea, major atmospheric air masses circulated between zones of low pressure (such as the Intertropical Convergence Zone) and high pressure (the South Atlantic Anticyclone). The circulation of the air masses produced the winds that created ocean currents (such as the Circum-Antarctic, the Benguela and the Mozambique currents). These atmospheric and oceanic dynamics have been the drivers of climate patterns over Africa throughout the Cenozoic Era (the past 66 million years). Through the Cenozoic, the climate has included warmer, wetter periods (known as ‘Hothouse Earth’) and cooler, drier periods (‘Icehouse Earth’) due to changes in the Earth’s planetary orbit around the Sun and the position of continents relative to the Poles and the Equator. The most recent major oscillations in climate, known as the Pleistocene Ice Ages, commenced 2.6 Ma and continue to this day.

The Shaping of Angola’s Landscapes

During the creation of Gondwana, and following the separation of the continents, further tectonic events caused uplift and erosion, and depression and sedimentation, of vast areas of the continental surface. In Angola, these uplift areas are today represented by the Mayombe and Bie Swells, and the Angolan Escarpment and Marginal Mountain Chain. The depressions include the Congo and Kalahari Basins. But for most of the Cenozoic, Africa has been relatively stable, with a slow downward erosion of the land surface to form the vast Central African Plateau, including Angola’s planalto and the extensive peneplains of the Congo and Zambezi upper catchments. The soils of these landscapes have been leached by the abundant rainfall and relatively cool and humid climate of the interior. The margins of these ‘old’ landscapes have been re-shaped by later erosional cycles, cutting the deep valleys of the Cuanza, Cunene and other westward-flowing river systems that drain the highlands. The ‘younger’ landscapes formed by the new erosional processes, themselves triggered by periods of coastal uplift, are characterised by soils that have not been heavily leached, and are therefore generally richer in nutrients. Their lowland situation results in them having climates that are warmer and drier than the highlands and peneplains.

Game-changing Evolutionary Innovations

The major climatic and landscape changes described above provided the stage for the evolution of Africa’s modern fauna and flora. Genetic differentiation, isolation, speciation and extinction accounts for continuous waves of terrestrial plant and animal families and species. However, several game-changing evolutionary innovations stand out and deserve mention. These innovations—C4 photosynthesis, hypsodont teeth, ruminant digestion—had dramatic consequences for the structure and functioning of African ecosystems.

The cooling and aridification of Africa during the mid- to late-Cenozoic led to an increase in the frequency of fire, the fragmentation of the forests, and, with enhanced rainfall seasonality, the formation of open savanna ecosystems. The stage was set by the new fire-driven ecosystems for physiological and morphological adaptations in plants and animals on a grand scale. These new ecological pressures and opportunities resulted in the evolution of the C4 photosynthetic pathway in sun-dependent and fire-tolerant savanna grasses. These physiological adaptations in turn resulted in high water-use efficiency, a key advantage in seasonally dry environments. These aridity-adapted grasses gradually out-competed the C3 grasses that had evolved in shady, humid forest communities. Because the plant tissues of the C4 grasses had a high silica content, and their leaves were often covered in gritty dust blown across the open savannas, they posed a challenge for grazing mammals. In addition, the leaves of these robust C4 grasses have high levels of cellulose and other structural carbohydrates, which are difficult to digest. Two further functional adaptations, during the Miocene (23–5 Ma), solved these challenges of gritty, indigestible grass, and led to the rapid radiation of mammalian herbivores, adapted to the open landscapes of Africa’s tropical savannas. By the development of high-crowned (hypsodont) dentition, the ungulates were able to make effective use of the gritty grasses, without the wearing down of their teeth. Secondly, equally important for herbivores in tropical savannas, was the development of the ruminant gut. Here a symbiotic relationship with microorganisms resulted in efficient use of savanna grasses. The microorganisms of the ruminant stomach possess a special enzyme, cellulase, that can break down the indigestible cellulose, thus leading to the success of African ruminants. By the end of the Miocene epoch, Africa as we know it, with its tropical savannas, and modern plant, bird and mammal families and genera, had been established.

Many further adaptations through natural selection provided the capacity to occupy the new landscapes created by large-scale geological and climatic changes. The outcomes are reflected in the functional traits that species exhibit—such as thick bark in mesic savanna trees, spines in arid savannas trees and shrubs, and complex physiological processes such as the temperature regulating carotid rete in desert antelope. At finer time and spatial scales, research on speciation in forest birds provides insights on the expansion and contraction of forests through wet and dry periods of the Pleistocene. Such knowledge, on forest dynamics and faunal speciation, is of increasing importance to strategic and systematic conservation planning to save Angola’s critically endangered Escarpment and Afromontane forests and their endemic fauna and flora.

At all scales, the processes of speciation through natural selection in response to climatic and geophysical dynamics, and competition for resources by plants and animals, underpins an understanding of ecological phenomena. Studies on the evolution of Angola’s rich biodiversity is not only of academic interest, but also directly applicable in conservation planning and management.

2 Contemporary Drivers of Ecosystem Structure and Function in Angola

The determinants of the distribution of species and ecosystems in Angola include:

  • Conditions (temperature and humidity) which influence the life of organisms but which cannot be consumed;

  • Resources (light, water and nutrients) which can be consumed and for which organisms compete; and

  • Disturbances (fire, floods, droughts, herbivory) which operate at the ecosystem rather than the individual level.

Here examples of key resources and disturbance pressures will be illustrated.

Resources: Solar Radiation and Energy

Life on Earth is possible because of the energy it receives from the Sun. The tilt of the Earth’s axis as it moves around the Sun creates the annual seasonality of climate, of day length, temperature and rainfall patterns. More directly, solar energy received at the Earth’s surface is harnessed through photosynthesis—the biochemical reactions that transform atmospheric carbon dioxide and water into carbohydrates, and release oxygen. The process of energy capture and transformation into simple sugars and cellulose in the chloroplasts of plant cells (primary production) is at the base of all food chains and the transfer of energy from one trophic level to the next. Plant tissues are consumed by herbivores, which in turn are consumed by predators, ultimately to be decomposed and mineralised by microorganisms or fire. The whole energy cycle is governed by the laws of thermodynamics.

The first law of thermodynamics states that energy cannot be created or destroyed, but can be transformed from one state to another. When wood burns, stored chemical energy is transformed into heat and light. In food chains, energy is used to do work—such as in growth, movement, reproduction and the production of complex molecules. Some of the energy is transformed into heat and is no longer available to do work. The total amount of energy in the system does not change, but the energy available to do work decreases from one trophic level (primary producer, consumer, predator, decomposer) to the next.

The second law of thermodynamics states that this transfer of energy through transformation reaches a point where there is no remaining usable energy for work. The deficit is continuously filled by energy derived from the Sun, through photosynthesis. At each step of the process—of energy transfer from primary producers to consumers, to predators and to decomposers—about 90% of the energy is used up as heat. Food chains are therefore short, usually of only three or four levels, due to the energy required for work being dissipated as heat in each transfer.

Resources: Atmospheric Systems and Rainfall

The macroclimates of Angola are driven by global atmospheric and oceanic dynamics, in particular the movements of air masses in relation to regions of low and high pressure. The Earth’s atmosphere exerts pressure on the surface. Areas of high and low pressure are caused by ascending and descending air. As air warms it ascends, leading to low pressure at the Earth’s surface. As air cools it descends, leading to high pressure at the surface. Air masses move from areas of high pressure to areas of low pressure, resulting in winds and ocean currents.

A low pressure belt over the Equator (the Intertropical Convergence Zone) draws in warm, moist, converging air masses which rise above the Equator, condense and result in the high rainfall received across northern Angola. A region of high pressure over the Tropic of Capricorn (the South Atlantic and Botswana Anticyclones) creates descending, dry air over southwestern Africa, and accounts for the aridity of the Namib Desert. The little rain which reaches the Namib comes not from the adjoining Atlantic Ocean, but from the Indian Ocean. Most of the rainfall from the Indian Ocean, carried across central Africa by easterly winds, is precipitated before reaching the Namib, which lies in the rain shadow of the highlands of eastern and central Africa. For the extreme hyper-arid coastal areas of the Namib, more moisture is received in the form of fog and low stratus clouds, than from rainfall. Fog and stratus clouds are driven over the coast by south-westerly winds. The moisture is trapped below a temperature inversion created by the cold, upwelling Antarctic waters of the Benguela Current. The south-westerly winds, and the Benguela Current, are driven by the air masses of the South Atlantic Anticyclone.

Resources: Soils and Nutrients

Soil is a primary resource essential for plant growth, survival and reproduction. The availability to plants of moisture and nutrients held in soils, determines the composition, structure and distribution of vegetation. Soil types, like vegetation types, vary widely in their structure and composition, and the distribution of soil and vegetation types is often highly correlated. In simple terms, soils consist of clays, loams and sands. Clays are usually darker, less permeable to water, and usually have higher nutrient content than sands. Sands are generally pale, quick draining and of low nutrient value. Loams are a mix of both clay and sand components. Two terms—eutrophic (neutral to basic pH, moderate to high nutrient value) and dystrophic (acidic, low nutrient value) are used frequently when referring to Angolan soil types. Based on these criteria, Angolan soils can be conveniently, if somewhat simplistically, divided into four soil groups, reflecting their broad distribution patterns and ecological characteristics.

  • Over half of Angola is covered by the nutrient-poor arenosols of the Kalahari sands of the interior peneplains, lying east of approximately 18° longitude. The sands were deposited by wind and water over the last five million years. These old peneplains receive from 800 to 1400 mm rainfall per year, and are highly leached. Despite being acidic and nutrient-poor, they support a robust cover of grasslands and woodlands.

  • Cutting longitudinally across the western highlands and planalto of Angola is a spine of crystalline rocks, including granites, gabbros, quartzites and schists. These rocks have produced highly leached ferralsols, low in nutrients and high in aluminium. They receive from 650 to 1200 mm rainfall per year. Ferralsols cover 23% of the country.

  • Further west, along the Angolan Escarpment, a mix of moderately fertile soils occur, on young, rapidly eroding landscapes, receiving 500–1600 mm per year. These landscapes have high agricultural potential, and once carried extensive rain forests.

  • The arid coastal lowlands, from the base of the escarpment to the Atlantic Ocean, comprise marine and terrestrial sediments, with moderate to high soil nutrient status. Rainfall ranges from 500 mm at the base of the escarpment to as low as 20 mm per year on the coast, where the sand seas of the Namib Desert dominate the landscape.

Disturbance: Fire and Herbivory, Equilibrium and Feedbacks

The importance of disturbance factors, such as fire and herbivory, has lacked emphasis in classical ecology textbooks. Yet fire, the great consumer of Africa, is the key determinant of structure in mesic savannas and is the environmental pressure that maintains a dynamic equilibrium between forests and savannas across northern Angola. Fire has an ancient history in global ecosystems, operating over hundreds of millions of years, most importantly as the environmental force that triggered the evolution of C4 grasses during the mid-Cenozoic (ca. 35 Ma) and the rapid expansion of tropical savannas during the past 10 million years. Multiple adaptive traits have evolved in mesic savanna trees and shrubs, in response to frequent fires. These include thick bark, epicormic buds, self-thinning, and geoxyles. These adaptive traits have evolved independently in multiple families both in African miombo and in South American cerrado ecosystems.

In arid savannas, fire is of less importance than in mesic savannas, although rare, intense, hot fires following unusually wet periods can have significant impacts. Grazing and browsing mammals are richer in species and of higher biomass in the nutrient-rich arid savannas than in mesic savannas. Herbivory is therefore of greater importance in shaping arid savanna structure than that of mesic savanna, and accounts for the evolution of defensive mechanisms against browsing, such as spines, thorns and prickles found on many tree and shrub species.

Linked to the processes of ecological disturbance are the concepts of equilibrium, resilience and feedback mechanisms. Ecological equilibrium is a state where an ecosystem may be subject to slight fluctuations in structure and composition, but returns to the original state when the disturbance (or perturbation) process ceases. The ability to return to the original state, and not change to a new state, is called resilience. Feedback loops play a key role in maintaining equilibrium. Frequent fires maintain an open landscape in tallgrass mesic savannas, even where there is sufficient rainfall to support closed rain forests. Negative feedbacks (such as fires in savannas that kill forest tree saplings) counteract change and maintain the status quo. Positive feedbacks (such as fire exclusion) amplify change from one stable state (open savanna) to a new alternative stable state (closed canopy forest).

Determinants, Pattern, Structure and Ecological Terminology

The interactions between resources and disturbance factors result in the diverse ecosystems, ecoregions and biomes found across Angolan landscapes. While the Guineo-Congolian forests and the Namib Desert are clearly distinctive in physiognomic structure and floristic and faunistic composition, the most extensive biomes, the Mesic/Dystrophic and Arid/Eutrophic savanna biomes are functionally distinctive but structurally rather similar. Both biomes comprise a mix of grasslands, savannas, woodlands and thickets. It is therefore important to address a significant challenge for Angolan students—the inconsistent use by ecologists of terms for ecological patterns, structure, processes and phenomena.

The early literature on Angolan vegetation adopted terms directly from Europe. However, Barbosa (1970) followed many of the terms used more broadly in Africa, and much of his terminology is followed in this volume. More recently, visiting scientists, predominantly from Europe, have applied the term forest to fire-tolerant miombo woodlands (the dominant ecoregion of Mesic/Dystrophic Savanna Biome), which are structurally and functionally distinct from the forests of the Guinea-Congolian Rain Forest Biome. In this volume, the term forest is reserved for the closed-canopy, stratified and fire-intolerant communities that lack a grassy ground layer—rain forests, gallery forests and swamp forests.

The modern definition of tropical savannas includes the co-dominance of fire-tolerant trees and C4 grasses in a continuum of grasslands, savannas, and woodlands. This definition is followed in this volume for the Mesic/Dystrophic and the Arid/Eutrophic Savanna biomes. The use of some collective terms for different levels of vegetation structure can, however, be confusing. This volume also uses the term savanna to describe grasslands with scattered trees. Until recently, the ecological and evolutionary distinctions between arid/eutrophic and mesic/dystrophic savannas were ignored by many ecologists, who placed all savanna ecosystems into a single savanna biome. For these reasons, an extensive Glossary of Ecological Terms is provided.

3 Ecological Patterns at African and Angolan Scales

Development of Angola’s Biomes

The end of the Mesozoic Era (the Age of Dinosaurs), some 66 million years ago, saw the extinction of the dinosaurs and the dawn of the Cenozoic Era (the Age of Mammals). Gymnosperms were being replaced by Angiosperms (flowering plants) as the dominant flora of the world. In tropical Africa, the vegetation cover changed from closed dark forests, to more open sunny savanna landscapes. The broad-leaved lowland forests are today represented by extensive rain forests, while the highlands carry remnant fragments of montane forests. As the African climate cooled, an arid savanna and semidesert flora evolved and occupied the hot, drier lowlands, while on the cooler and more humid plateaus, mesic savanna woodlands were established.

Today, Angola includes representatives of six of Africa’s nine biomes: Guineo-Congolian Rain Forest, Afromontane Forest and Grassland, Mesic/Dystrophic Savanna, Arid/Eutrophic Savanna, Namib Desert and Mangrove biomes. The biomes can be characterised by structural and functional features, which can be observed through the medium of satellite imagery. The main structural types include forest, thicket, woodland, savanna, shrubland, grassland, mangrove and desert. Closer study reveals regional centres of floristic endemism. These include the Guineo-Congolian, Afromontane, Zambezian and Karoo-Namib regional centres of endemism. While centres of endemism are defined by their floristic composition, and are explained by evolutionary relationships, biomes are defined by ecological structure and function, determined by the conditions under which they grow, the resources available to them, and the impacts of disturbance factors.

While this coarse-grained classification of African and Angolan biomes and regional centres of endemism provides a useful introduction to the continent’s ecological and biological diversity, it must be recognised that at the interfaces of biomes and centres of endemism, broad transition zones and mosaics occur. This is especially the case where the closed-canopy Guineo-Congolian Rain Forest Biome forms a mosaic with the open woodlands and tallgrass savannas of the Mesic Savanna Biome. Throughout this volume, emphasis is placed on predominant patterns and processes, rather than the frequent exceptions to these.

Recognising Biomes and Ecoregions in the Field

A helpful starting point in learning to recognise patterns in nature, and the division of biomes into ecoregions, is observation at the landscape scale. This can be facilitated by the use of satellite imagery and aerial photography, scoping down to low altitude, where topographic features and vegetation structure can reveal patterns from continental to local scales. However, ground-based fieldwork should always be the primary source of ecological information. A working knowledge of the key landscapes, geological formations and soil types, and plant and vertebrate species of one’s study area, is essential. For this reason, in the description of biomes and ecoregions, reference is made to the key abiotic and biotic features that characterise the units. The challenge to learn to identify plant and animal species is not insurmountable. For all biomes and ecoregions, a shortlist of indicator plants, birds and mammals can be focused on.

By way of example, the main biomes of Angola can be identified by the presence or absence of a few tree species. The vast miombo (typical of the country’s Mesic/Dystrophic Savanna Biome) is identifiable by the presence of mupanda (Brachystegia spiciformis). The Arid/Eutrophic Savanna Biome is recognised by the presence of imbondeira (Adansonia digitata); the Guineo-Congolian Rain Forest Biome by moreira (Milicia excelsa); and Afromontane Forest Biome by pinho-de-muxito (Podocarpus milanjiana). With the addition of a few more tree species, the ecoregion can be identified, and confirmed by reference to a few bird, mammal or reptile species. Some ecoregions are characterised by single tree species, such as the Zambezian Dry Evergreen Forests (Cryptosepalum exfoliatum), the Angolan Mopane Woodlands (Colophospermum mopane), and the Zambezian Baikiaea Woodlands (Baikiaea plurijuga). Ecological studies that ignore the identity of the subject species, especially the indicators, have limited utility.

4 Patterns at Landscape Scale in Angola

Recognising patterns at both spatial and temporal scales is fundamental to understanding ecological phenomena. The interactions between termites and grasses within a 5 m diameter ‘fairy circle’ of the Namib Desert are as intriguing as those between the precipitation, soil nutrient, herbivory and fire regimes of the arid/eutrophic and mesic/dystrophic savannas that cover over 90% of Angola’s land area. Temporal scales range from hundreds of millions of years, such as in the development of Angola’s geological foundations, to the milliseconds of molecular activity in photosynthesis. The following concepts, phenomena and interconnections are mentioned to illustrate that scale is a fundamental concept in ecology, and a reason for students to gaze across landscapes as well as to peer down microscopes.

The Catena Concept

The landscapes of the Angolan planalto and peneplains are characterised by a dense pattern of soil and vegetation sequences. A catena (chain) is a repeated series of soil forms across gently rolling landscapes, with woody communities on the rises and treeless grasslands in the valleys. The pattern reflects the soil formation processes of leaching, transport and deposition of water and nutrients across the soil profiles of upland, slope and bottomland. Fire, and in some locations frost, are also factors maintaining the vegetation pattern.

Duricrusts: Laterites and Silcretes

An important edaphic feature of many ferralsols and arenosols is the presence of impervious duricrusts (laterites or silcretes) at a metre or more below the surface. These cemented bands result in a barrier to tree growth, because of impeded drainage (causing seasonally anaerobic, waterlogged soils), but also because the duricrusts prevent root penetration and limit root access to moisture during the extended dry season.

Termitaria as Nutrient Hotspots

The low nutrient availability (dystrophic) status of mesic savannas accounts for the importance of nutrient hotspots in an otherwise uniform cover of miombo trees and grasses. The concentration of nutrients is due to the activity of termites that gather the limited clay particles of the sandy soils, plus organic material, in building their colonial nests (termitaria), that total between 100 and 1000 nests per hectare. The nutrient concentration of salts in the termitaria has been recorded as 20 times higher than the surrounding soils of the miombo. As a result, many mammal species use the old termitaria as salt-licks, while a great diversity of plants, vertebrates and invertebrates form distinctive habitats around the larger termitaria—biodiverse islands in a sea of low-diversity woodlands. In the miombo woodlands of Zambia, for example, over 700 tree species are associated with termitaria.

Mycorrhizae, Termites and Miombo Trees

Mutualistic associations exist between tree roots and fungi (mycorrhizae) in nutrient-poor mesic savannas, most typically in the dominant miombo trees—Brachystegia and Julbernardia. These mycorrhizal interactions are complex. Mycelia (networks of fine root-like hyphae of fungi) encircle or penetrate the root hairs of trees and transfer to the trees nutrients sourced from organic matter. Some species of termites create fungal gardens within their nests, feeding the fungi with organic material that the termites collect from the plant litter of the surroundings. These termite/fungal/tree associations maintain a robust woodland in an otherwise dystrophic savanna. The reproductive organs of the fungi (better known as mushrooms) provide a seasonal source of food for local human populations.

Geoxyles: Underground Forests

A further phenomenon unique to the mesic/dystrophic savannas of Africa and Brazil is that of ‘underground forests’. These are communities of geoxyles—dwarf shrubs that form extensive carpets of brightly coloured leaves and flowers which appear after fires and before the rain season. Geoxyles occur from the highlands of Benguela to the floodplains of Moxico—and across Africa to Mozambique and northwards to the Sudan—wherever mesic/dystrophic savannas are found. The dwarf shrubs are often closely related to the trees of the adjoining woodland. Geoxyles protect their growing points by keeping them, plus their branches and woody storage organs, below the soil surface. The Angolan miombo has possibly over 200 species of geoxyles, belonging to more than 40 plant families. They, like their Brazilian counterparts, evolved over the past five million years. Their unusual morphology has puzzled ecologists for 150 years and, despite strong arguments that the geoxyle habit is an adaptation to fire, nutrient poverty, high water table, herbivory, or frost, or combinations of these factors, the explanations proposed thus far remain contested.

Age and Diversity of Guineo-Congolian Rain Forests

With regard to the Guineo-Congolian rain forests, perceptions of the age, stability and floristic diversity of the extensive forest blocks of the Congo have been clarified during the past two decades through palaeoecological, archeological and phylogenetic studies. The belief that these forests represent ancient, exceptionally species-rich and stable ecosystems has been countered by evidence that the forests underwent major contractions and expansions through the Pleistocene. Furthermore, during the Holocene, human activities of agriculture, hunting and iron smelting brought significant changes to forest composition and structure. Large areas of monospecific tree communities point to deforestation followed by secondary succession with single tree species dominating the community for hundreds of years. The perception that much of the forest represents a stable climatic climax of the vegetation has been shown to be incorrect. Further, the richness of the African rain forest tree flora is less than a quarter of that of the Neotropics, within a similar land area. The relative paucity of tree species of African rain forests remains a topic of debate. These forests are nevertheless richer in bird, mammal and amphibian species diversity than those of any other African biome.

Mesic/Dystrophic and Arid/Eutrophic Savannas Compared

Emphasis has purposely been given in this volume to the mesic/dystrophic savannas, which cover over 80% of Angola, compared with arid/eutrophic savannas, which cover 13% of the country. However, the ecology of Africa’s arid/eutrophic savannas is better known to scientists that the miombo and similar ecosystems, perhaps because of the concentration of ecological research over past decades in large conservation areas such as the Serengeti and Kruger National Parks, where arid/eutrophic savannas dominate the landscapes.

What is evident is that studies comparing the patterns and ecological processes in the two savanna biomes highlight the importance of rainfall, soil texture, nutrient status, fires and herbivory on their structure and functioning. Fire is a key determinant of habitat structure in mesic savannas, but less important in arid savannas. Herbivory by grazers and browsers, in contrast, is a driver of vegetation structure in arid savannas, but has comparatively little influence in mesic savannas. Nutrient cycling in arid savannas is via decomposer organisms, mostly invertebrates, but in mesic savannas, is largely driven by fires and mycorrhizae. It is these dichotomies in ecological processes and responses that make the tropical savanna biomes of Angola such attractive fields for research.

5 Ecological Concepts and Theories Relevant to Conserving Angolan Species

Two centuries have passed since Alexander von Humboldt first published ideas on the relationships between global vegetation patterns and climate, and since the schoolboy Charles Darwin started collecting plants and animals and asking questions about the origins of species. Over this time a substantial body of ecological concepts, theories and laws have been proposed and tested, accepted or rejected. Dozens of excellent textbooks are now available on the history, scope and application of the fundamentals of ecology. In this volume only a selection of the key elements of ecology are described. Even fewer of these can be mentioned in this synopsis, where emphasis is given to those with immediate relevance to the study, documentation and conservation of Angolan species and ecosystems.

Species Richness and Endemism

The measurement of species richness, and the explanation of why some communities have more species than others, are basic activities in ecological study. Related to measurements of species richness are measures of their abundance, density, evenness and distribution. Species with very limited areas of distribution, and which are restricted to a single country or biome—endemics—have long held the interest of conservation biologists. Very few analyses of species richness and endemism have been undertaken in Angola. The knowledge base is notoriously fragmented, and vast areas of Moxico and Cuando Cubango provinces lack anything more than preliminary surveys. Even for the country’s iconic plant, Welwitschia mirabilis, extensions to its area of occurrence continue to be made, as previously unrecorded populations are found. The richest biome of Angola, the Maiombe rain forest of Cabinda, has not been surveyed since the 1970s. Comprehensive species inventories are not available for any national park, beyond preliminary checklists of a few vertebrate groups. Recent efforts to synthesise knowledge on Angola’s biological diversity (Huntley et al., 2019) provide testimony of the country’s natural wealth, and to the urgent need to survey, document and effectively protect it.

Threatened Species and Hotspots

Emphasis had been given by conservation scientists to identifying species whose survival is threatened by overexploitation, land transformation, invasive species or other causes. Preliminary Red Lists of Angolan plant and vertebrate species have been prepared, but lack data with which the degree and pace of threat can be determined for the majority of species. What is evident is that many Angolan mammals are in peril of extinction, if they are not already extinct. No sightings have been made, in the past several decades, of Lowland Gorilla, Lichtenstein’s Hartebeest, Puku, Angolan Giraffe and Black Rhino. Other species (Forest Buffalo, Forest Elephant) are known only from very small and isolated populations. However, remarkable recoveries have been achieved. The country’s most threatened mammal—Giant Sable—has been rescued from imminent extinction by meticulously planned, dedicated and long-term programmes (Vaz Pinto, 2019).

Local concentrations of endemic and threatened species are designated as global (or national) biodiversity hotspots. Efforts have been made since the early 1970s to identify Angolan hotspots, and to motivate for their detailed survey and proclamation as conservation areas. Several of these (Lagoa Carumbo, Serra do Pingano, Morro Moco, Namba, Cumbira) have attracted government attention, but still lack effective conservation measures. Actions to implement proposed management plans for these hotspots are urgently needed.

Theories of Island Biogeography and of Metapopulations

Two ecological theories—of island biogeography and of metapopulations—deserve more intensive application in conservation research in Angola. The theory of island biogeography is relevant to planning and management of conservation areas for the relict ‘islands’ of Afromontane forests of the Angolan highlands. The theory is based on the balance between immigration to, and extinction on, islands, whether they are oceanic islands or isolated forests in fire-prone savannas. As the remaining fragments of these forests decline in area and structure, so too do the chances of maintaining viable breeding populations of endangered species. Isolation further limits immigration of recruits to the forest patches, and together with habitat transformation, has resulted in local extinctions, as recorded for bird and mammal species on Mount Soqui and Morro Moco.

The concept of metapopulations is closely related to that of island biogeography. It is applied to all the local populations of a species that are separated from other populations of the same species by some form of disturbance or barrier. For each population, there is a minimum viable population size needed to maintain genetic diversity. Connectivity between populations is essential to maintaining the species’ gene pool. Angola has many species that are fragmented, even though they survive in very small, declining populations across extensive ranges in Angola. These include Lion, Cheetah, Forest and Cape Buffalo, and Forest and Savanna Elephant. The populations of all these species are threatened by local events, whether within the population structure (demographic) or due to random (stochastic) environmental dynamics. The conservation of these species within their natural range in Angola will require initiatives such as those implemented to rescue the Giant Sable population of Cangandala National Park.

6 Conclusions: Why Ecology? An Opportunity for Young Angolan Students

Two of the key questions raised in the introduction to this book should challenge and motivate the student: Why is an understanding of ecology critical to Angola’s sustainable development? Why ecology? Here a concluding, personal remark is offered. Having been involved in ecological research and biodiversity conservation projects for the past 55 years, I have often paused to consider whether an ecological understanding of Africa’s fauna and flora, and of its landscapes and biomes, is of any importance to ecosystems, economics or society. Like many ecologists across the globe, I have witnessed the rise and fall of wildlife populations and habitats, which, in all cases, were the result of political and not science-based decisions. I have suffered from occasional moments of frustration, even despair. But repeated examples of success rise above the continent’s dismal record of failure. The rescue and conservation of Angola’s Giant Sable population, and the restoration of Gorongosa National Park in Mozambique, are but two examples of good science, visionary leadership and indefatigable perseverance paying rich dividends (Huntley 2023).

Success is possible. But sound and innovative research, and above all, good governance, is needed to underpin any conservation effort, and to reverse the negative impacts of the processes eroding the biodiversity of Africa. The continental trends—of deforestation of forests and woodlands for agriculture, timber, fuelwood, charcoal and curios; of the overpopulation of domestic livestock and degradation of the productive capacity of rangelands; of the bushmeat trade that is creating ‘empty forests’; of invasive plants infesting forests and agricultural lands; and of the global problem of climate change—demand a convincing response from conservation professionals based on science rather than on passion.

The diversity and richness of Angola’s natural living resources and biomes have few parallels in Africa. What the country lacks is a strong body of active ecologists—young professionals dedicated to working in the field rather than in an office—using the vast literature on African ecosystems to stimulate and guide their curiosity and energy. This volume is therefore a humble attempt to support the process of ecological training and the implementation of effective conservation efforts in Angola.