As with animals, each species of plant has its favourite conditions. External factors determine where each species thrives, and where it will perish. These include temperature, light, water, soil type, nutrients, and which other species of plants and animals live in the same area. Species with similar needs are often found together, in communities which are characteristic of that particular environment. Namibia has a number of such communities, or typical 'vegetation types', within its borders – each of which is distinct from the others. East of the desert, some of the more common include:
The dominant tree here is the remarkably adaptable mopane (Colophospermum mopane
), which is sometimes known as the butterfly tree because of the shape of its leaves. It is very tolerant of poorly drained or alkaline soils and those with a high clay content. This tolerance results in the mopane having a wide range of distribution throughout southern Africa; in Namibia it occurs mainly in the higher, slightly wetter areas including Etosha, the northern Kaokoveld, Caprivi and the Kalahari.
Mopane trees can attain a height of 25m, especially if growing on rich, alluvial soils. However, shorter trees are more common in areas that are poor in nutrients, or have suffered from extensive fire damage. Stunted mopane will form a low scrub, perhaps only 5m tall. All mopane trees are deciduous, and the leaves turn beautiful shades of yellow and red before falling in September and October.
Ground cover in mopane woodland is usually sparse, just thin grasses, herbs and the occasional bush. The trees themselves are an important source of food for game, as the leaves have a high nutritional value – rich in protein and phosphorus – which is favoured by browsers and is retained even after they have fallen from the trees. Mopane forests support large populations of rodents, including tree squirrels (Peraxerus cepapi
), which are so typical of these areas that they are known as 'mopane squirrels'.
This all-encompassing category refers to those areas of dry, thorny woodland that occur when trees and shrubs have invaded open grassland, often because of some disturbance like cultivation, fire or over-grazing. It could be subdivided further into Thorntree
and Mixed Tree and Shrub Savannah
Some form of savannah covers much of the Namibian highlands, and the dominant families of trees and bushes are the Acacia, Terminalia (bearing single-winged seeds) and Combretum (bearing seeds with four or five wings), but many others are also present.
In a few areas of the Kalahari (including some within Khaudum National Park), the Zambezi teak, Baikaea plurijuga
, forms dry semi-evergreen forests on a base of Kalahari sand. This species is not fire-resistant, so these stands occur only where slash-and-burn cultivation methods have never been used. Below the tall teak is normally a dense, deciduous thicket of vegetation, interspersed with sparse grasses and herbs in the shadier spots of the forest floor.
Moist evergreen forest
In areas of high rainfall, or near main rivers and swamps where a tree's roots will have permanent access to water, dense evergreen forest is found. This lush vegetation contains many species and is characterised by having three levels: a canopy of tall trees, a sub-level of smaller trees and bushes, and a variety of ground-level vegetation. In effect, the environment is so good for plants that they have adapted to exploit the light from every sunbeam. In Namibia, this occurs only as riparian forest
(sometimes called riverine forest
), which lines the country's major rivers.
A 'vlei' is a shallow grass depression, or small valley, that is either permanently or seasonally wet – though Namibia's vleis are drier than the areas that one would call vleis in countries further east. These open, verdant dips in the landscape usually support no bushes or trees. In higher valleys amongst hills, they sometimes form the sources of streams and rivers. Because of their dampness, they are rich in species of grasses, herbs and flowering plants. Their margins are usually thickly vegetated by grasses, herbs and smaller shrubs.
Floodplains are the low-lying grasslands on the edges of rivers, streams, lakes and swamps that are seasonally inundated by floods. Namibia has only a few floodplains, in the Caprivi area. The best examples are probably beside the Okavango in Mahango, and near the Chobe and Zambezi rivers in the Impalila area. These contain no trees or bushes, just a low carpet of grass species that can tolerate being submerged for part of the year.
Though not an environment for rich vegetation, a pan is a shallow, seasonal pool of water with no permanent streams leading into or from it. The bush is full of small pans in the rainy season, most of which will dry up soon after the rains cease. The Etosha and Nyae Nyae pans are just much larger versions, which attract considerable numbers of migrant birds when full.
Weighty tomes have been written on the flora of the Namib Desert, with its endemic plants and multitude of subtly different vegetation zones. One of the easiest to read is Dr Mary Seely's excellent book The Namib
, which is widely sold in Namibia. This is well worth buying when you arrive, as it will increase your understanding and enjoyment of the desert immensely.
Distance from the coast and altitude are crucial to note when looking at the Namib's flora, as both are factors in determining how much moisture a plant receives by way of the fog. This is maximised at an altitude of about 300–600m above sea level, and extends up to about 60km inland. Thus the communities of vegetation can differ widely over very small distances: the plains full of delicate lichens in one place, and empty a kilometre away. Adaptations to the extremes are all around: wax-covered leaves to reduce transpiration, hollow stems to store water, low growth to avoid the wind, slow growth to take advantage of the infrequent moisture.
Many will become familiar to even a casual observer; none could forget the prehistoric welwitschia (Welwitschia mirabilis
), the kokerbooms silhouetted on rocky mountainsides, or the strange halfmen seen in the far south.