Site Selection, Survey and Treatment Plan - Afforestation, Reforestation and Forest Restoration in Arid and Semi-arid Tropics - page 65

area, and year of creation—should be displayed on it. Provision for an inspection
path should also be made, indicating the layout of the path on the map. Length and
alignment of the inspection path should be such that the entire area can be inspected
conveniently. The inspection path should be motorable as far as possible.

3.8.3 Soil and Water Conservation Works

Soil and water conservation (S&WC) measures are the heart of afforestation work
in arid and semiarid areas. These will vary from site to site and therefore each site
should include in its treatment plan carefully designed S&WC measures. Decisions
regarding the specifications of work items and their quantities must be made care-
fully. Quantities are to be estimated on the basis of the surveyed site plan, whereas
specifications will almost exclusively be determined by the terrain, the soils, and the
basic aims and objectives of the programme.
Digging of pits is required in most plantations, except in sand dunes. Size of the
pits and their spacing and alignment are important issues to be decided. The treatment
plan should also include an estimated number of pits that will be accommodated in
the site. Pitting area is determined by deducting from the total area the area that is
not suitable for pit digging (e.g. areas that have no soils, are too steep, form beds
of streams, or have abundant natural rootstock). Apart from this, the area covered
by other S&WC structures such as the contour trench is further deducted. The net
pitting area is then divided by the product of the spacing between the pits in the two
directions to get the estimated number of pits.
Size of pits is determined by a trade-off between cost and effectiveness. A larger
pit is more effective in moisture conservation but at the same time it costs more. It
is not possible to carry out a break-even analysis to determine the optimum size of
the pit because no quantitative measure of the effectiveness of moisture conservation
can be developed. Past experience is the only guide in this matter, based on which
pit sizes should be standardised.
Spacing of pits should be determined on the criteria of soil and moisture availabil-
ity, species used, aims and objectives of the programme, and the density of natural
rootstock already existing in the area. In plantations to be raised with the specific
aim of production of timber, poles, pulpwood or fuelwood, however, the spacing
considerations may be more complex. Where thinning is to be carried out for a final
crop spacing, the initial spacing may be half the final spacing. For energy plantations
where biomass produced is to be maximised, a close spacing—say, 1.5 m in both
directions—may be appropriate. In most conservation-cum-production plantations in
arid and semiarid tropics using xerophytic species, the average spacing could be 3 m
in either direction. This could be increased to 4 m 5 m in case of broadleaf species

with a larger crown. Even so, a uniform prescription of spacing cannot be justified
inasmuch as the climate and the soil type determine the final spacing as observed
in natural stands of trees. Every ecosystem—a piece of land for that matter—has
a carrying capacity for tree population. No matter how many trees are planted in a

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