Constant change is the driving force in the history of savannas, and some conception of the future can be gauged from evidence of past changes and from trends experienced today. Geological history reveals major global and regional climatic changes, the most recent of which include glacial advances and retreats that influenced savannas even though their greatest impact was in higher latitudes. Since the last glacial retreat around 20 Kya and within the historical record, there have been oscillations of temperature and rainfall that have come to light from sediment cores, evidence of past vegetation in pollen or diatom profiles, and in rock paintings and other archaeological evidence. Physical and biological processes that are currently affecting savanna regions include persistent changes in climate, especially rainfall patterns and temperature increases; reduced discharge of rivers and lowering of water tables; shifts in the ranges of plants, their phenology, and growth; losses in biodiversity; declining crop yields and desertification.
The pace of these changes is occurring faster than that considered as the result of natural variation. Whereas some climatic and environmental changes can be anticipated from knowledge of these trends, many human interventions are relatively new within savannas and introduce pressures whose long-term effects are unknown. Our stewardship of these resources depends on clear information and assessment, and a combined approach integrating the interests of all those who live in or utilise savanna resources.
The potential futures for savanna landscapes may be depicted as two interconnected sets of processes: variations caused by natural events, and changes resulting from human activities.
Climates have varied over time and differ in each regional location, but there is consistent evidence that present day global variations are having repercussions throughout all savannas. The report from the Intergovernmental Panel on Climatic Change (IPCC) in 2014 tried to distinguish human impacts from those caused by natural changes. It comes to the unequivocal opinion that anthropogenic pressures are accelerating climatic change. The principal directions are increases in global temperatures and changes in atmospheric composition, which have knock-on effects for the environment and on human societies. Long-term effects that particularly influence savannas include accentuating seasonality with more extreme temperatures and rainfall patterns, together with changes in atmospheric CO2 concentration. More immediate changes are likely to result in increased storm intensity and variations in global influences such as the ENSO events or the ITCZ. Natural climatic changes have usually been over a period long enough for vegetation to adapt or diversify, and for animals to have a chance to migrate, whereas human actions are more immediate and can have radical impacts on climate, land use, and wildlife.
The IPCC estimate that it is likely global surface temperatures will increase by 1.5°C (with some projections suggesting 2°C), by the end of the 21st century relative to the situation from 1850 to 1900. While these temperatures lead to moderate impacts, a rise of 3°C would result in marked losses in biodiversity and the benefits offered by what are grouped as ecosystem services. The impact of temperature rises beyond such levels falls within the realms of informed guesswork but almost certainly with a much worse scenario. Global warming is largely caused by the emission of greenhouse gases such as carbon dioxide, nitrous oxide, and methane. Variations in the global water cycle are predicted to increase disparity between warm and wet regions, and between wet and dry seasons, with distinctions between different regions. Much of the increased energy is likely to be dissipated into the oceans, leading to thermal expansion, which, together with the melting of ice sheets, is forecast to affect low-lying savanna coastlines through rising sea levels.
The probable mean sea level rise from 1900 and 2010 was 1.7 mm y−1 according to the IPCC, but rose to 3.2 mm y−1 between 1993 and 2010. Future predictions to 2100 suggest a rise of between 0.44 m and 0.74 m depending on the level of emissions. By 2200 this forecast rises to well over 1 m. These estimates exclude storm surges and what are termed singular events (such as the total deglaciation of Greenland). These figures may not seem at first to be very urgent, but there are many savanna areas that are close to the coast and would experience increased flooding and salt water incursions, including many vulnerable settlements. For example, the height of Belize City in Central America is only around 20 cm above mean sea level, and that figure itself has been whimsically referred to as being built on ‘mahogany chips and broken gin bottles’ from its colourful past. Much larger cities have also been shown to be vulnerable, such as São Paolo in Brazil, located at the eastern edge of the cerrado, or Darwin on the margins of the northern Australian savannas. Coastal savannas are widespread around the Caribbean and Australia and are to some extent protected by fringing mangrove that, in contrast to savanna vegetation, seems able to cope with gradual changes in sea level.
Increased concentration of CO2 in the atmosphere affects plant growth by influencing photosynthetic rates and this has sparked a lively debate as to its role in savanna vegetation. Concentrations of CO2 in the atmosphere have varied considerably over time: grasslands expanded during low CO2 concentrations, as during glacial periods, and forests amplified during interglacials. Experimental and simulation studies predict increases in the number of woody species and related biomass as a result of greater atmospheric CO2, assuming there is sufficient moisture. The advance of woody species into grassland can be correlated with the history of industrialization and gas emissions, as shown in studies from South Africa. At the same time there are predictions of savanna expansion at the forest fringes with the onset of drier climates, especially where coupled with land use changes (as forecast for eastern Amazonia). Vegetation transformations in more arid savannas appear to be less clearly linked to CO2 and may be driven by over-grazing. Some dry savannas seem to have remained stable over decades such as the Australian woody savannas and open grasslands. It is likely that CO2 levels will increase beyond what has been described as the ‘evolutionary experience’ of savanna plants, and therefore that we could witness a decrease in C4 plants and a loss of grass-dominated landscapes. Nevertheless modest increases in CO2 could be argued to be beneficial overall, since vegetation stores more carbon resulting in greater biomass. The upper limits of this photosynthetic balance are far from clear.
Climatic change also affects the impact of fires. With seasonally increased temperatures, greater evaporation, and diminishing soil moisture, fires are able to override climatic influences in places where there is sufficient combustible material built up during wetter periods. The humid savannas are generally more productive and thus generate a greater quantity of organic matter, whereas more arid savannas have fewer fires because they lack as much combustible material. Savanna trees are generally distinct from evergreen forest, in function as well as species composition, and they adapt to burning except in extreme conditions. High fire incidence favours the development of underground storage tubers and other protective measures as well as affecting species composition. Savanna soils act as important C-sinks and biomass changes above ground are likely to be reflected in as yet inadequately quantified subsurface variations. Following disturbances such as fires, an increased CO2 concentration would favour tree growth over grassland. The colonization of open areas by trees is also helped where woody plants can expand from wetter sites such as galleries or damp depressions. Where fire frequencies are restricted, there has been widespread expansion of woody vegetation responding to climate over recent decades in many but not all savanna regions. Despite increasing information on these trends, it is extremely difficult to predict where the changes may occur due to the interaction of a multitude of factors, and this makes management of savannas a complex and multiple-scaled endeavour.
Many of the savanna landscapes have already been greatly disturbed or completely transformed as depicted in Chapter 6. Trends portray sweeping shifts in land use that affect not only the plants, animals, and human settlements dependent upon savanna resources, but also impact on the global economy. Reports from international agencies such as the UN (Millennium Ecosystem Assessment), IPCC (Climatic Change), or the WWF (Ecosystem Assessments) amongst numerous other groups, concur on the need for an integrated approach to dealing with the concerns encompassing both biological and social issues, but warn of factors that are threatening solutions.
The transformation of natural savanna landscapes has resulted from a relatively small number of major activities. Possibly the most widespread activity is pastoralism, which has taken place for thousands of years in parts of the African savanna but which has reached more commercial proportions in modern farming practices. Some of the New World and Australian livestock farms occupy enormous areas, with the concomitant dangers of monoculture such as lack of biological diversity and buffering against pests and diseases. Similarly increasing cultivation for cash crops has limited the resource base of savanna regions across the globe and resulted in monotonous, biologically limited landscapes (see Figure 30). Despite this increasing pressure on land, there are still many areas with resident indigenous people practicing smallholder farming, some of whom live in protected areas and National Parks. More exotic land uses include mining, which takes on a different character depending on the product and location, but is always exploitative at the expense of the environment, along with the urban development and expansion of infrastructure. Over recent years there has also been growing recognition of the wider range of ecosystem services that the savannas can offer, pointing to the value of environmental, social, cultural, and aesthetic benefits beyond economic resources. There have been many attempts to put a value on nature, but not much consensus as to the best way forward. Whilst it can be argued that many of the activities are necessary for the economic well-being of the countries, it is equally obvious that a balance needs to be struck between transformation, addressing social and economic aspirations, and conserving the biological resources.
The main concerns that could impact upon the savannas have been identified by the IPCC and other international and local agencies. They can be reduced to a number of key issues.
Coastal savanna areas. These are identified as being at risk of flooding and salt-water incursions. Yet several developments help to alleviate these problems. The greatly increased accuracy of weather forecasting from satellite data has enabled early warning to be given to vulnerable communities, such as the hurricane warnings in Middle America or cyclones in northern Australia. Similarly the level of information and media communication (through television, radio, and mobile phones) has reached out to almost all communities in what were previously isolated and remote areas.
Food security and food production systems. Increased desiccation threatens all plant growth and agriculture has always been a challenge for vulnerable areas in savanna regions. The wetter savannas have sufficient water but lack nutrients, whilst the dry areas often have more potentially fertile soils but lack water. Land degradation through processes such as leaching and soil erosion frequently results from the depletion of land cover. Land surveys and monitoring from satellites with multispectral sensors at practical scales using GIS now provide more accurate and up-to-date information. Many of the problems appear to have a measure of technical solution (fertilization, organic matter management, restoration, soil moisture control). However, these are usually costly and beyond the reach of smallholder farmers, who rarely have access to credit, and most assistance seems to be directed towards the larger producers. The development of new and modified crops, better storage and marketing, and multiple land use schemes could potentially help all scales of farming. Conflicts over land tenure are an endemic feature of many tropical areas and in some countries land registration surveys have alleviated some of the disputes but there are many instances where land is claimed by several competing owners. The involvement of international agencies such as the FAO or CGIAR (representing an influential group of agencies), and the increasingly active role of NGOs, has significantly helped to relieve the problems of food security with better information and communication of techniques.
Loss of biodiversity. This is a widespread issue throughout savannas and is scrutinized in a recent report to the EU concerning the worsening situation in Africa (see the citations in websites given in the ‘References and further reading’ section). Whereas most of the countries in the sub-Saharan Africa are signatories to the various international environmental conventions and IUCN outlines, there are widely divergent levels of implementation. The report identifies trends which can be mirrored in most of the world’s savanna regions—a steady erosion of plant and animal wildlife along with increased pressure on land and natural resources. The report points to the value of protected areas (PAs), which represent the most intact assemblages of African wildlife, but it also recognizes that many indigenous groups consider such reserves to be imported concepts that should not interfere with traditional ways of life. It is clear that for PAs to flourish there have to be tangible benefits for local people. Environmental- and eco-tourism have offered some opportunities, where people are compensated for damage in return for protecting wildlife or where there is significant tourist revenue. Other initiatives that potentially offer some return for local people include extending the UN REDD (Reducing Emissions from Deforestation and Forest Degradation) proposals to savanna woodlands and more open savannas, especially if the value of soil organic storage becomes better appreciated. The most promising approaches seem to be strengthening the National Parks and other PAs through long-term funding, especially from wealthier external stakeholders, with better reserve design and connecting corridors. The Transfrontier Conservation Areas, first initiated as the South African Peace Park in the 1990s, is currently being expanded with a possible eighteen potential schemes. Public and Private Partnerships also offer means of engaging with local people and incorporating monitoring and research.
Conservation issues. The arguments surrounding conservation and development stand out amongst global concerns. They are well illustrated in the Brazilian cerrado where well over 50 per cent of the vegetation has already been transformed into planted pastures and agricultural cash crops. The rate of deforestation is greater than that in the much more widely publicised Amazonian forest, and less than 3 per cent of the area is under any legal protection. This has entailed a high environmental cost with fragmentation of remnant vegetation, soil erosion, increased leaching and soil compaction, water pollution, greater frequencies of fires, and imbalances to the C-cycle. Many habitats are sensitive to change affecting many of the essential pollinators such as bees. The loss of biodiversity is exemplified by the elimination of native varieties of cassava (Manihot species), which is one of the world’s major food crops. On a more positive note, a number of alleviating forces have been at work and are growing in influence. While it would be unrealistic to imagine that the conversion of land into farming will cease, there is a better awareness of the importance of retaining biodiversity, better understanding of agricultural practices, and the adoption of different techniques such as minimum tillage and agroforestry. There is also growing awareness of the value of indigenous knowledge and of the contribution from different ethnic groups and opinions. Introduction of some of the invasive African forage grasses is also being closely monitored including Melinis minutiflora, which has a particularly disruptive impact on native herbaceous communities. There has been a growing influence from a network of NGOs, and some state governments, notably Goias, have been active in promoting more sustainable measures. The protected areas are in danger of being surrounded by converted land and so there are plans to develop wildlife corridors (such as between the cerrado and the Pantanal). The greatest advance, however, has possibly been the worldwide recognition that savanna biodiversity is important ecologically, culturally, and economically, and that there is widespread publicity to conserve as much of the natural resources as possible.
Urban expansion. The rapid increases in the proportions of people living in towns and cities are transforming many of the savanna landscapes. Many urban immigrants live in what are euphemistically termed ‘informal settlements’ (i.e. squatter districts). The greatly increased population and growth rates in sub-Saharan Africa are largely directed to the urban areas. The movement from rural to urban areas is having a significant impact on savannas and the trend is unlikely to diminish. Once again international agencies have been active in promoting schemes for integration, despite this being perceived as a ‘top-down’ approach. In the end it becomes a national issue requiring political solutions.
Human health and security. Problems associated with these issues have been accentuated with increased temperatures, less predictable rainfall, and greater numbers of storm events. An upsurge in abnormal climatic events and their environmental consequences has alerted international communities to the need for practical measures and rapid response mechanisms. The occurrence and intensity of such eventualities varies widely over the savanna, but for example Central America is picked out as being ‘one of the most responsive tropical regions to climatic change’. Coastal lowland savannas are clearly at greater risk. A number of proposals have been made to counter the causes of threats with a number of international agencies involved such as the UN and FAO. The most immediate problems have been identified as population growth and poverty; poor governance and/or weak legislation and enforcement; inadequate land tenure and resource rights; conflicts and violence; water shortages; disease and political indifference.
A balanced approach would ideally embrace the whole of the savanna landscape rather than individual components. Over the broad canvas of contemporary ideas, there are many practical suggestions for limiting population growth (partly by raising living standards) and focusing on the key elements essential for conservation. There is a strong case for a Key Landscape Conservation approach, together with the African model of Transfrontier Conservation Areas and designation of individual sites of outstanding value. It is evident that any form of sustained conservation, however well integrated and inclusive, is going to require stronger administrative controls and legal frameworks. At the same time it will be necessary to tackle corruption and criminal activities, whilst dealing with issues such as bushmeat and fuelwood which are part and parcel of the livelihoods and traditions of many people. Since the landscape and the political boundaries rarely coincide, it is often necessary to examine individual aspects separately and then to seek integration. It is also usually necessary to compromise between opposing interests and to find the ‘Middle Ground’, as eloquently advocated by Reid for East Africa.
While many of the current concerns are to some extent being addressed, and the worst impacts of natural and human change better understood, most measures are mitigations not solutions. Forecasting the fate of savannas is a risky proposition, yet the trends outlined are likely to persist and probably magnify. It remains difficult to be optimistic about future alternatives for the savannas when political instability, population growth, and demands on the land continue to outweigh resources. The concept of a savanna landscape is evolving from one that is natural to one that is manipulated. In all likelihood it will become a totally anthropogenic landscape and therefore one where we cannot escape responsibility for its husbandry. Savannas are landscapes to rejoice in and wonder at but they also need to provide a livelihood as well as a world resource.