The increasing shortage of wood for all purposes in many areas of Africa has been a serious matter for a number of years. The most practical solution is to plant quick-growing trees to provide local fuel and pole needs. These can be planted in large blocks or in smaller areas by family or kraal units. Kraal and farm woodlots are the most important means of providing for local woodneeds.
In much of Africa, and indeed over most of the world at one time or another, natural woodland has been the age old source of building materials, firewood, tools and simple furniture. Almost as important, it provided a wide variety of plant medicines and food supplies. Particularly important in times of crop failure, items such as fruits, edible roots and honey.
The cutting down of trees and firing of woodland were inevitable in making available crop and grazing land. In earlier times, with fewer people, the practice of shifting cultivation or chitumene, was reasonably sound agricultural practice in savannah woodland regions. The trees were felled and crops planted and harvested for 2 to 3 years then the clearing abandoned. When there were very few people it was not necessary to use the same piece of land again for maybe 30 or 40 years by which time the woodland had grown up again and the soils had fully recovered their fertility. But as the population grew this very long ‘bush fallow’ period was not possible. The practice continued but the woodland never had the time to recover before it was again cut back for crops. This stage marked the beginning of the progressive and heedless destruction of Africa’s naturalwoodland.
- CHOOSING THE RIGHT SITE
Plantations of trees are just as much of a crop as maize or cotton. The crop has to be planted, weeded and harvested. The only difference is that the tree is not harvested every year but has to grow for several years until it is big enough to be cut for poles and firewood.
It is important to plant the right tree on the right site and given below you will see a table showing which tree is the best for various annual rainfalls and soil depth on the site.
|Annual rainfall (mm)
|Soil Depth (metres)
|Over 1 000
|700 to 1 000
|700 to 1 000
|Less than 1.5
|600 to 700
|600 to 700
|Less than 1.5
|500 to 600
|Less than 500
|Tree planting not recommended
Two factors are used to decide what species of tree to plant. The first is the annual rainfall the second the soil depth. Deep soil helps to make up for low annual rainfall, so that you can plant a tree that would otherwise need higher rainfall to grow well. Remember that rainfall often varies quite an amount in an area depending on the particular place. The figures you use should be good local records for annual rainfall and not a general figure for the region. If a local rainfall figure is available it should be an average over at least ten years as rainfall varies a great deal from year to year as well as from locality to locality.
- No site should be chosen which is within 30 metres of a watercourse or vlei, owing to high water use of these trees, and the general inadvisability of cultivating alongwater-courses.
- Areas with annual rainfall of less than 500mm are considered as unsuitable for successful tree plantations.
- Indigenous trees in the area can give very useful indications. Plantation trees will not grow in shallow or waterlogged soils or soils of poorfertility.
The soil depth available for the tree roots is most important. Rooting may be restricted by layers of stones, reddish-brown hard layers of laterite, heavy clay usually grey in color which causes water logging. The upper layer of soil, some 10 to 30cm, is called the topsoil and contains much of theplant foods necessary for the growth of young tree seedlings. In choosing a site for tree plantations remember that the trees also provide shade and shelter from wind. Honey may also be a by-product as bees are fond of gumtrees.
Fencing of some sort is essential to keep cattle, sheep and goats out of gum plantations. Cattle can quickly destroy a young plantation by trampling and smashing the young trees. Goats chew leaves and shoots and tear off the bark. Post and wire fencing is expensive but fencing can be done with thorn branches or other suitable material.
A basic rule is to use strong healthy seedlings of the right size to establish your plantation. It is wise to plant early as soon as the soil is thoroughly moist down to 30 cm. You need the right sized seedlings, that is, 25 to 30cm tall at the time of planting, which is normally late November or early December. This in turn means sowing the seed early enough to produce the right size plant by late November to early December. For those who want to raise their own seedlings locally the work in what is called a tree ‘nursery’, is described in Lecture 5.
It will not be possible to plant early unless the site has been prepared in good time. Ploughing the site, after any necessary stumping, should be carried out in March or April at the end of the preview rains when the soil is still soft enough to allow easy working. Final preparation with harrowing or hoeing out of weeds can then be carried out in October or early November.
The object is to have strong, healthy seedlings about 25 to 30cms tall by the time planting is possible. Make a stick 2,5m long (or as many 2,5m sticks as there are people to assist) and mark where the trees are to be planted. When the soil is wet down to 30cm and the seedlings have their roots appearing, planting canstart.
The polythene tubes containing the seedlings can easily be removed by rolling the tube gently between the hands to loosen it from the soil, and then gently pulling the tube or sleeve over the top of the plant.
Black polythene tubes or pockets can often be used again and again, which is a big saving.
On no account should any container be left on the seedling as this will restrict the root system and can cause the death of young trees some years later.
There is no doubt that young gum trees cannot stand competition from grass and other weeds. Other trees, in particular pines, can stand grass and weedcompetition.
Only seedlings in containers should be bought and should have a minimum height of 15, 20 to 25cm being a satisfactory size range. The most usual container is a black polythene open-ended sleeve, with closed end pocket. If the seedlings are ready for planting the roots should be visible at the bottom of the sleeve or coming out from the holes in the bottom of the pocket. If termites are a problem in or near the planting area the seedlings should be treated with a recommended insecticide, either in the nursery before going out to the planting site (this is preferable), or on site before planting. The suspension should go into the containers and not onto the ground which is ensured by stacking the containers on level ground close together.
Figure 1: Measuring the distance between pits or hole for planting with a 2,5m stick
Figure 2: Removing container carefully
Figure 3: Plant placed in pit so that surface of container soil is at same level as the ground
Figure 4: Replacing soil around the plant
Figure 5: Making sure that the soil is firm around the plant