|Special Public Works Programmes - SPWP - Planting Trees - An Illustrated Technical Guide and Training Manual (ILO - UNDP, 1993, 190 p.)|
|2. Preparing the planting site|
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).