twist, however: whereas market research typically deals with private goods
most of whose benefits accrue to users (e.g., cars, toothpaste, hamburgers),
CV focuses on goods and services that have a value not only to users but to
society in general, and part of the value is not related to any form of present
or future use.
The next three sections present illustrations of how the methods described
here have been used successfully to measure the economic value of agroforestry
systems in a variety of contexts and regions. More information about these
and other methods can be found in Bateman et al. (2002).
Agroforestry Systems in Practice I:Acacia senegal
in the Sudan
Acacia senegalgrows in the Sahelian-Sudanian zone of Africa. When cut, the
tree releases a sticky gum in defense of the wound, and the gum, known as
gum arabic, has multiple uses ranging from confectionery, lithography, and
beverages to pharmaceuticals and pesticides. It is superior to the gum released
by Acacia seyal,which produces a gum known as talha. Collecting gum arabic
is an important feature of farming systems in the Sudan. It is especially impor-
tant for small farmers in the “gum belt” of central and western Sudan, where
gum gardens are part of a bush fallow rotation with other crops. At any one
time, farmers devote some land to crops, some to A. senegal,and some to fal-
low.
A. senegalis remarkable for the multiplicity of benefits it produces. Apart
from gum arabic, these include leaves and seed pods for livestock fodder, fuel-
wood, conservation of soil because of deep tap roots and lateral root systems,
nitrogen fixation with consequent effects on grass growth near the trees,
microclimatic protection from shelterbelts, and dune fixing. The roots of the
tree have been used to line water wells.
Gum arabic systems have been analyzed in a number of studies. Pearce
(1988) estimated an internal rate of return^1 of 36 percent for combined gum,
fodder, and fuelwood production, which is extremely high for investments in
developing countries. Barbier (1992) notes that any analysis cannot be truly
representative of gum agroforestry practices because of the sheer diversity of the
various combinations that are practiced in the gum belt. In addition, A. senegal
varies in its production of gum by age and type of soil. Barbier therefore ana-
lyzes returns to gum and crop production for several regions (Table 4.1).
The results are shown in two forms: in financial terms (i.e., by looking at
revenues and costs in Sudanese pounds) and in shadow price terms (often
called economic returns). The idea of shadow pricing is that domestic prices
may not represent true economic costs. For example, a worker paid a wage, if
not employed in this occupation, may be otherwise unemployed. The oppor-
tunity cost of the worker then approaches zero because he or she would not
76 II. The Ecological Economics of Agroforestry