Page 208 - Area 9 - Relevant Document

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Areas where the practice is relevant

These technologies are relevant in all areas where cultivation takes
place on sloping land.

Establishment and spacing

To be effective as tree strips, trees should be planted in lines along the
contours. The spacing between the contour "tree strips" is determined
in the same way as for other soil-conservation structures. Within rows
spacing can be 0.1-0.2 m for shrubs and 0.5-1.0 m for trees. If the
trees are combined with grasses or shrubs the spacing can be wider,
and the spacing should also be wider in dry areas because of moisture
competition between the trees.

The spacing for trees and shrubs intended to stabilize terraces can be
1.5-3.0 m for trees (including banana, pawpaw and guava), and 0.3-
0.5 m or wider for shrubs if the farmer so wishes. Initial
establishment can always be denser and thinning can be carried out
later to obtain the final spacing. On steeper slopes an option is to grow
trees on every second terrace to avoid having too great a density of
trees.

Management aspects
The trees are managed in the same way as trees in fields. Shrubs
must be trimmed almost as though they were in a live fence in order
not to occupy too much land.

Benefits
Which of the many possible products and services can be obtained
from the trees will depend on the choice of species. The role of
stabilizing structures is important. If perennials are grown on bunds,
for example, the structures will become more permanent and will be
respected by tractor drivers when they are ploughing.

Examples of species

Basically the same as for trees in fields, but more fruit trees can be
added, e.g. bananas, Citrus spp., Psidium guajava (Guava),
Cyphomandra betacea, and Carica papaya (Papaya). On steeper slopes,
preference should be given to trees which either will not grow very big
or to trees that can be pollarded since it is desirable to have a high
density of trees. The steeper the slope, the shorter the horizontal
interval between the soil-conservation structures, so if trees are grown
on all the structures more trees are required per hectare to stabilize
them.