Savanna vegetation is adapted specifically to the location and characteristics of the region. The climatic variation means that the vegetation has a short life cycle, in which the primary aim is to conserve water to survive. However, the majority of the plants are xerophytic. This is characterised by small, spindly leaves, with waxy layers to reduce evapotranspiration. Trees have gnarled trunks to reduce water loss, e.g. the baobob, which has a 10m diameter trunk to store the maximum amount of water possible. They also have extensive root systems to absorb as much water as possible. Vegetation cover starts high above the ground to reduce animal destruction. For example, the acacia has leaves which start 5-7m above the ground. Plants do not waste energy on fruits, but rely on annual fires to spread their seed. The diurnal variations of climate, e.g. temperature ranges, humidity, wind velocity, all require flexible approaches to minimise the effects of evapotranspiration to preserve water.
Many plants are pyrophytic to survive the fires. Many of the fires are started by farmers deliberately to create more farming land. They see burning as a way to increase their acreage, and thus their income. Forest and woodland is cleared for a variety of motives, to create agricultural and pasture land for example, but the most serious cause of desertification in this respect is the so-called fuelwood crisis which is characteristic of many drylands in the developing world. The collection of fuelwood from urban hinterlands in the Sahel, the most severely affected region, has resulted in the almost total loss of trees around major cities. Examples include Ouagadougou (Burkina Faso) and Dakar (Senegal), while the radius of the treeless zone around Khartoum in Sudan is 90 km (56 mi).
The debate on the link between climate change, or climatic variation, and desertification is inconclusive. 70% of the problem of desertification can be attributed to natural events such as uncontrollable climatic events and population growth. It is clear that population growth puts pressure on natural resources in drylands in at least two ways. Firstly, increased population means an increased demand for food, which has to be produced by increasing productivity (yield per ha) or production (area under cultivation). In most cases, the additional food comes from the latter, including an expansion into marginal and fragile lands that are highly susceptible to degradation. Secondly, increased family size means a parcelling of land resources with each subsequent beneficiary owning an increasingly smaller plot, which is then over-cropped.
This demand means that the bush fallow system suffers. Whereas the bush would normally be left in fallow, i.e. unused, for up to twenty years, the increased pressure means that the crops are rotated to utilise the bush more, giving less recovery time. The nutrients disappear from the soil, and the crop becomes worse, forcing the farmer to rotate even more. With a shortage of capital resources, poor people exploit their limited resources to meet immediate and pressing needs even if such short term exploitation compromises the long-term stability and viability of such resources. Hence, poverty has an indisputable impact on desertification. Declining commodity prices and unfavourable trade terms, could, and do, encourage or compel dryland farmers in developing countries to degrade their land resources in the race to produce more to increase dwindling returns from increasingly poorly- priced primary production. Pastoral nomads, e.g. the Maasai Mara, have no choice but to find the best resources for their cattle, or to lose the herd, and thus their lives, since they are subsistence agriculturists. This means that they migrate to find the best parts of the bush area to use. Once they have exhausted the resources available, they migrate again, leaving behind an overgrazed landscape, which will take years to rejuvenate itself.
The political instability of the region does nothing for the benefit of the land. The results of civil wars include vast refugee camps, which destroy large areas of savanna, and perhaps even scorched earth policies, which leave large areas infertile for years. In addition, the soils of the region do little to aid. The ferruginous soils require annual nutrient inputs to sustain the same amount of crops each year. Without the annual fallow, the nitrogen is unlikely to remain in the top layers of the soil, and is liable to be leached out. Thus the soils become progressively worse.
The savanna vegetation is adapted to cope with variable climate conditions and progressively declining human care. The influence of anthropogeny upon the natural vegetation has had far reaching effects. The Sahelian problems of the late 70s and early 80s have highlighted the importance of retaining the savanna as a boundary between rain forest and desert. It is a particularly resistant environment to natural problems, but increasingly being overused by humans.
'Geography - An Integrated Approach by David
Waugh. 3rd edition, published by Nelson
Microsoft Encarta Deluxe 1999.