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Ecoregions of Zambia

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Through Ecoregion, Natural environment and Climate

Physical environment

The main aspects of the physical environment which determine the biomes and ecoregions of Zambia are: climate, specifically rainfall amount, length of the dry season, and temperature, which is related to elevation; and soils and bushfires.

Climate

Rainfall

Rainfall amount is the most important determinant of the type and distribution of ecoregions. Zambia experiences good rainfall, with extremes of 500 to 1400 mm (most areas fall into the range 700 to ) in a distinct rainy season of four to six months centred on January, when the moist Intertropical Convergence Zone is over the country. The highest rainfall is in the north (about 1200 mm –- all figures are annual amounts), especially the north-west (1400 mm), decreasing towards the south (around 700 mm); the driest areas are in the Luangwa and middle Zambezi valleys (500 mm). None of the country is arid.

Dry season and drought resistance

The dry season lasts 6–8 months, divided into the cool dry season or winter from April or May to August, followed by the hot dry season, September to November. Most rivers, lakes and swamps are permanent, except in the hotter, drier south. Along the banks of permanent rivers and in the spray of waterfalls are evergreen thickets similar in character to tropical rainforest, relics of a wetter past. In dambos (grasslands found in most of the country) and other marshes, soil water is available throughout the dry season, but they may be rather acidic. Elsewhere, plants and animals are adapted to the long dry season. For plants this includes the deciduous habit (losing leaves to conserve water), very deep root systems, water-storing roots and tubers, waxy leaf cuticles, and drought-resistant seeds. Succulent plants are also widespread, especially in rocky areas. For animals, adaptations to drought are seen in migration and breeding patterns, as well as the ability, found in rodents and reptiles especially, to obtain water requirements from food without the need to drink. Hibernation through the dry season is practiced by some amphibians and invertebrates. The latter may also survive the dry season through drought-resistant forms.

Temperature and elevation

The elevation of the great central African plateau on which Zambia is located, typically between 1000 and 1300 metres, modifies temperatures, which are lower than for coastal areas at the same latitude, and pleasant for much of the year. On the plateau (covering about 80% of the country) mean minimums for June in the cool dry season are in the range 6–12 °C, mean maximums for October, the hot dry season are 28–35 °C. Frost only occurs on a few days in winter on the highest exposed hills, or more widely in the lower humidity areas of the southern half of the country. Plants susceptible to frost do not grow in the southern half of the country. Otherwise temperature by itself is not a great determinant of plant and animal distribution. Temperatures are higher at lower elevations, such as the Luapula-Mweru and Mweru-Wantipa/Tanganyika valleys in the north, and highest in the lower Luangwa and Zambezi valleys in the south, typically experiencing 40 °C in October. One way in which temperature affects the distribution of large mammals is through the distribution of the tsetse fly, which, within its range is found in hotter valleys rather than the higher, cooler plateau. Species susceptible to trypanosomiasis are not found in such valleys.

Soils

The broad types of soil found in Zambia are:

  • red sandveld soils cover most of the country, and are generally not very fertile due to weathering and leaching; the top soil is sandy and is more fertile where the top soil has a higher clay content.
  • Grey dambo soils contain more nutrients but are waterlogged in the rainy season and often very acidic, restricting the plants which can grow there to sedges and wiry grasses tolerant of marshy conditions.
  • Black soils of floodplains are fertile, grasses grow on them as soon as the annual flood recedes and provide a rich resource for herbivores. If the annual flood is disrupted by dams, woody shrubs of lower nutritional value tend to replace grasses and so reduce the number of herbivores and biodiversity.
  • Kalahari Sands in the south-west of the country are infertile and do not retain moisture, so are dominated mostly by deep-rooted trees with little growth in the understorey. Grasslands both flooded and non-flooded also occur there .

In areas where soils are waterlogged for all or part of the year, or are very infertile, sandy or acidic, they take over from climate as the predominant factor in determining the distribution of plants and animals. Such communities are said to be edaphic, and are found on grey dambo soils, black floodplain soils and Kalahari sands.

Bush fires

Bush fires range across most of the country in the later dry season, escaping from "chitemene cultivation" and caused by villagers burning off crop residue or hunting, as well as by lightning strikes. The vegetation is adapted to it, particularly the grasses, and at that time of the year deciduous trees have lost most of their leaves and so usually do not suffer extensive damage. Prevailing winds are not usually very strong and a lack of a great deal of dry fuel on the ground (since most areas are burnt annually it does not build up) means that the fires are not as devastating as in countries such as Australia and the south-western USA.

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