|Special Public Works Programmes - SPWP - Planting Trees - An Illustrated Technical Guide and Training Manual (ILO - UNDP, 1993, 190 p.)|
|2. Preparing the planting site|
The planting site should be completely prepared and ready for planting when the first rains are due. There are two reasons for this - first, because there is a rather short time interval in which the plant should be planted to get the best possible start; and second because the rainy season is the most work-intensive in rural areas and it is good to have as much work as possible done before it starts. Site preparation should give the young trees a good start and rapid early growth. The measures needed differ between different types of sites and between different types of plantations. The following measures may be taken:
- Clearing vegetation
- Ground preparation
- Marking where to dig the holes
- Digging holes
- Water conservation
Marking where to dig the holes
On most sites trees, bushes and grass have to be cleared away to prevent them from competing with the young plants. This is very important when using light-demanding trees such as Eucalyptus, Pine or Cupressus. If more shade-tolerant species are chosen, existing trees do not have to be cleared.
Total clearing of the grass and bushes is needed on moist grassland sites and for species sensitive to grass competition, like some Eucalyptus.
On sites where ground vegetation is below one metre, it is normally sufficient to clear patches around the plants or strips along the lines of plants. The strips should be about one metre wide. Patches a radius of about 1 metre radius can be cleared with the hoe when digging the planting hole.
Between the cleared patches and strips the vegetation should be cut short, except on sites where reduction of the vegetation may result in increased erosion. There the vegetation between the cleared patches should be left as intact as possible.
Existing trees should only be removed when they seriously disturb the development of the plantation. Around water sources a vegetation belt of at least 15 to 25 metres should be preserved. Trees along rivers and old trees providing shade and beauty should always be saved.
Save trees around water sources
Tools required for clearing and grass-cutting
The type of tool used should be adapted to the land of vegetation that is being cleared.
A brush hook might be the best tool to use for cutting underbrush up to 20 cm in butt diameter. The weight of the brush hook is about 1.2 kg. The handle is about 0.6 m and the blade 0.2-0.3 m. The top of the blade is formed as a hook. This will protect the edge if it hits a stone. The hook also permits the worker to cut small brush with a pulling jerk. The brush hook is used with two hands.
A machete can be used for cutting hard-stem grasses and woody weeds. It is a long knife, also used for many other purposes, such as cutting fence posts, trimming live fences and root pruning. The machete weighs about 0.6 kg. The traditional machete has a handle of 0.1-0.15 m and a blade of 0.45 m in length. For grass-cutting a modified model has been developed. On the grass-cutting machete the length of the handle is about 0.5 m and the blade about 0.3 m. A grass-cutting machete is used with one hand and the long handle allows the worker to maintain an upright position. Productivity can be increased if the cutting is assisted by a wooden stick (see fig).
Tools for clearing and grass-cutting
A scythe is useful for soft stem grasses. A scythe with a short blade (0.3 m) is chosen when the terrain is rough and the grass dense. In even terrain a longer blade (0.6 m) can be used. This will speed up the work. It takes some training to get used to the scythe, but once the technique is mastered productivity is good. The worker should stand with his back straight and feet apart. To give power to the cutting swing, the muscles of the thighs and the back should be used. The hands are used mainly for guiding the swing, not for powering it. A well designed scythe is adjustable to individual preferences and body sizes. In the middle of the handle there is a grip for the right hand, and at the top there is another grip for the left hand (for right-handed workers). The upper handle should reach the arm pit and the lower should be placed one underarm's length lower.
A slasher is a double-edged tool, suitable for cutting short grass. It has only limited applications in tree planting. A slasher weighs about 0.6 kg, the length of the handle is around 0.8 m and the blade 0.05-0.1 m. Holding the slasher in one hand, the worker swings it back and forth in a sweeping motion.
Hoes, for completely removing vegetation on strips or patches, are described in section 4.1.
Tools required for clearing and grass-cutting
Ground preparation is needed to soften the soil, and to allow the roots to affix firmly and deeply. Since nutrients are washed out in the surface soil layer, it is also important to mix soil for the deeper layer with soil from the surface layer to guarantee availability of the nutrients needed by the seedling.
The method depends on the site and the species planted. Usually digging holes and uprooting grasses with the planting hoe about one metre around the planting hole is enough.
The work should be carried out along the contour line, not up and down the slope, otherwise rain water may start to wash away the soil and form gulleys.
In sites with crusts, hard pans or other hard soil layers it may be necessary to use mechanized soil preparation. For this a bulldozer, a sub-soiler or a scarifyer drawn by a tractor can be used.
Work along the contour lines
Tractor with scarifyer
It is not always necessary to mark where to dig the planting hole. A well instructed planting crew working on well cleared ground may plant without premarking the planting spots. They may space the distance using tool handles or footsteps as measures for the planting work.
Even if it is necessary to mark on the ground where to dig the planting holes, there is no need for accurate distances. It is more important to find the best planting spot available for the plant. In sites with a lot of vegetation it might, however, be preferable to plant in straight rows and with a fixed distance between the plants, since this will make it easier to find the plants during weeding.
Determine how many handle lengths or steps should separate the trees. Then make a mark on the ground with the planting hoe. The planting spots can also be marked out by sticks or pegs.
If the soil is not too hard, the holes might be dug in advance during the dry season. This will reduce the need for labour during the actual planting. They can also be dug at the same time as the actual planting. How to dig holes and examples of the different tools to use are described in Chapter 4.
Marking where to dig holes
Digging of holes
In arid and semi-arid areas it is almost impossible to get the seedlings to survive without some water conservation measures. In high rainfall areas and on unstable soil, particularly on slopes, the soil often needs to be protected against erosion until the tree crowns shelter the site. The aim of all soil and water conservation measures is to reduce or retard the flow of surface run-off water (water harvesting). This will diminish the erosion damage and cause the water to soak into the soil, increasing the amount of soil moisture available for the seedling.
Microcatchments can be built in dry locations to trap the water around the seedlings. They vary in shape and size and are relatively small and cheap. If well constructed, they should last about five years, which will give the plants tune to become well established.
Contour ridges or diguettes serve as small dams to keep water from running downhill. They consist of ridges dug out of the hill slope along the contour lines and are used in heavy soil with low permeability.
Bench terraces are series of narrow, more or less horizontal steps cut into the hillside.
It is extremely important to space ridges and terraces properly. If the structures are placed too far apart, they will be washed away or broken. If they are placed too close, labour and land will be wasted.
Some guidelines of how to construct soil conservation structures are given in Technical sheet 2. However, the size, type and spacing of earthwork structures always have to be adapted to local conditions. Consult the national extension agencies for soil conservation, soil survey and forestry for more detailed advice.
Water conservation structures
Terrace with trees and crop
Common mistakes when preparing the planting site
Insufficient site clearing and soil preparation.
Agricultural tools are used that are not suitable for the kind of work and the soils found in tree planting.
Tools used have handles of inconvenient size, poor shape, badly fixed and cutting edges are not regularly sharpened.
Soil and water conservation are too sophisticated and expensive for tree planting. Water conservation measures used uniformly rather than adapted to erosion risk (bigger and more closely spaced where risk high, widely spaced or none at all where risk low).