1. TIMBER TREES OF SOUTHERN AND CENTRAL AFRICA
Unfortunately, the indigenous woodlands of Southern and Central Africa contain very few tree species which can be exploited commercially on a large scale. This is because the more valuable species are sometimes so widely scattered that it does not pay to harvest them. It should not be forgotten that this natural woodland plays a highly important part in the lives of many thousands of rural families, who rely upon it for timber for houses, cattle kraals, household effects, fuel-wood, fruits and medicines. The very rapid rate at which this woodland is disappearing is therefore of grave concern.
The indigenous hardwood woodland is thus rich in species but poor in terms of timber productivity. The rate of growth of indigenous trees is extremely slow. They are often subjected to fire and generally have a poor shape. Much of the timber is unsuitable for the major part of industrial requirements. Even the timbers of the commercially important hardwood species have only limited uses. To supplement the inadequate indigenous timber resources and provide more versatile types of wood, man-made forests or plantations of exotic trees, i.e. trees from outside the region, have beenestablished.
All timbers fall into two main groups; the hardwoods (from broadleaved trees) and softwoods (from coniferous trees). These are rather confusing terms because although most broadleaved trees have a harder denser wood than most coniferous trees, this is not always the case. The true differences lie in the actual cell structure of the two types of wood. The conifers (pines, cypresses, firs) were the first trees to evolve on earth and were followed later by the broad-leafedspecies.
THE INDIGENOUS HARDWOODS
Only three indigenous tree species are harvested on any scale. The demarcated forests are worked on a sustained yield basis, so that only as much timber is taken out as is being replaced by the growth of younger trees. Rainfall in most of these areas is generally less than 600mm per annum. All three species are much slower growing than the exotic trees, taking about 100 to 150 years or more to reach maturity and only reaching heights of about 15 – 20 metres. The timbers are much heavier and harder than that of most of the exotictrees.
Mukwa, Kiaat, Bloodwood
This tree is very widely distributed growing in South Africa (where it is known as Kiaat), Angola, Mozambique, Malawi, Tanzania, Zambia and Zimbabwe.
Mukwa is a very handsome furniture wood with a worldwide reputation. It has a fine finish and maintains stability towards changes in the water content of the atmosphere. With such a valuable timber, which takes so long to grow, veneer is the most economical way to use the wood.
This is not related to the true teak of India and Burma which is much lighter and more versatile. It grows in the Zambezi valley in Zambia and also in Angola and Botswana. The wood is very heavy and hard.
It is some 50% heavier than mukwa and about twice as heavy as pine or poplar. It is a reddish-brown wood and makes a decorative floor and has a high resistance to wear, very durable and resistant to termite attack. It is also used as railway sleepers and sometime for furniture.
Zimbabwean Mahogany, Mchibi
This is not a true mahogany. The name probably refers to the red colour of the wood. This species has the same properties as teak. The timbers are very similar as are the densities and has the same uses.
Interest has also been shown in the utilisation of Msasa timber. This tree is common and widespread in Zimbabwe, Zambia and Mozambique and it reaches its largest size in the Kalahari sand areas. The timber is suitable with the proper preservative treatment as railway sleepers and has also been successfully peeled forplywood.
Small quantities of timber from the following savannah woodland trees have also been exploited commercially from time totime:
A reddish-brown durable wood used for veneer, furniture and flooring blocks.
Figure 1: Pod mahogany
A very hard, heavy dark purple to black wood, similar to ebony. Mainly used for carvings and musical instruments.
Figure 2: African Blackwood
Extremely light, pale-colored wood used for making curios and toys.
Yellow to greenish-brown, hard and close-textured and is a popular carving wood.
EXOTIC PLANTATION TREES
The exotic species on which plantation forestry is founded in the region are relatively few in number. There are three main pine species, a few eucalypts, black wattle and very small areas of poplar. The commercial planting of exotic timber is generally restricted to areas with rainfall in excess of 700mm per annum.
The plantations start to produce logs which can be used to make pulp at about 8 years of age and logs which can be sawn into board at about 13 years. The large yields of sawn timber come from a final felling at about 30 years.
Pine timber has high strength for its weight and is easily planed, cut and nailed.
Mexican, or spreading-leaved pine
This pine comes from central Mexico but has been widely planted in South Africa and Malawi and Zimbabwe. It is the most popular variety of pine.
Figure 3: Mexican or Spreading-leaved Pine
Comes from the south-eastern United States and is more suited to lower altitudes and more shallow and poorly-drained sites than the Mexican pine willtolerate.
Figure 4: Slashpine
This tree grows naturally over a wide area in the south eastern United States and is the principal commercial timber species in the south of the country. It is likely to be planted on a much larger scale in Africa in the future and is suitable for areas similar to those in which the slashpine is grown.
Figure 5: Loblolly pine
A pine which has a good potential for commercial planting in the better softwood areas of medium altitude (1 100m to 1 500m) low to medium rainfall (600mm to 900mm) is the Pinuskeysiafrom South-East Asia and the Philippines.
Eucalypts have been far more widely planted in southern and central Africa than any other exotic
hardwood even more than the conifer introductions. About 100 species of eucalypt have been introduced on a trial basis but only about 12 have shown commercial possibilities. Of these, the salignais the most important.
Eucalyptus grandis, Saligna gum or salignal
This tree came to South Africa about 80 years ago. It was for a long time called Eucalyptus saligna, but botanists now tell us that the tree is known as Eucalyptus orandia. This is not only the fastest growing tree in the region, but takes the world record for the shortest time taken to reach 100 feet (30.48 metres); in only 5 years from planting. This shows the enormous potential of this tree on good average sites. The tree is used mainly in pole form for power transmission, telephone poles and fence poles when treated with creosote preservative against termite attacks and rot, can be used in mining and the sawn wood is used for boxes, crates, pallets, furniture and as a raw material for the chemical pulp industry. The timber is heavier than pine and is light red incolour.
Figure 6:Eucalyptus(gum) Figure 7: EucalyptusSaligna
This tree is a native of Australia that has been planted extensively in South Africa and Zimbabwe for its bark, an extract of which is used in tanning leather. It requires high rainfall and mist belt conditions for good growth, i.e. areas which have a substantial amount of mist and light rain during the Winter months. When grown for bark the tree is harvested after about 10 years.
Figure 8: Black wattle
Carolina Poplar, (Southern Cottonwood):
Although the common name of this exotic tree is Caroline Poplar, it grows naturally over a much wider range than this name indicates, from Southern Canada right down to Louisiana in the United States.
It needs a rich, deep, well-watered and well-drained soil. The wood is white, straight-grained and of even texture and is about the same density as pines. Its main use is for match splints. The timber has a combination of properties which are not easily found and commands a good price.
Most commercial farms have areas of indigenous woodland. If any do not, then a lot of money and energy has been spent in digging out trees in order to improve the grazing. However, if you want more grass on your farm, then undoubtedly some of the trees must come out, but not all. It is possible to achieve a balance between woodland and grassland on your farm to the benefit of both communities. We must learn to treat our forests as a crop to be used and also to be renewed. They must be tended as carefully as we tend our farms.
A farmer may well ask why he should need to grow wood. One answer would be the cost of firewood. His bill for firewood bought for compound fuel, for tobacco curing, boilers, kitchens and dairies would be enormous. In addition he requires poles for houses for poultry runs and every kind of shelter.
If you want only firewood from your woodland, the routine is easy. Fell everything, even the big trees. Fell the trees at ground level and trim the stumps. All branch wood and slash that is too small for firewood should be dragged into heaps or lines and very carefully burnt off. A few months after felling the stumps will throw up new shoots, or coppice. In addition, many species will send up shoots from underground roots especially if the ground between the stumps is disturbed. These new shoots will be your future timbercrop.
Grass can be controlled by early burning in the woodland area. It is possible to exploit the improved woodland if it is sufficiently dense removing the occasional straight young trees for poles and the older trees for firewood. Indigenous woodland can be brought into the farm plan as windbreaks between arable lands or pastures. The woodland on the farm should be preserved for its conservation value, i.e. control of surface water run-off during the rains and the general stability of the soil, for the browse and fodder it may contain and lastly its value as a sanctuary for animal and bird life, which are both valuable assets on the farm.
Table 1: Benefits of woodland products to rural communities:
|Low cost in use, produced locally at low cash cost.
Substitutes for costly commercial fuels
Substitutes for agricultural residues
Maintains availability of cooked food
|Low cost in use
Produced locally at low cost
Substitutes for costly commercial materials
Maintains housing standards
|Conservation, food, fodder, grazing
|Protection of cropland against wind and water erosion
Complementary sources of food, fodder and forage (e.g. in dryperiods) Environment for supplementary food production – (e.g.honey)
Increased productivity of marginal cropland
Diversifying the community economy
|Inputs to local handicraft, cottage and small-scale industries, (plus benefits from saleable products)