Environmental Engineering Reference
In-Depth Information
outputs (for example, manure, milk, transport). Although not explicitly
stated, this approach again followed a production function approach
where the outputs from the livestock production were directly related to
the inputs. By multiplying the outputs of livestock production by their
price, and subtracting the costs of production, the total proi tability of
each management system was calculated.
In addition to the valuation of direct-use resources, some research has
also been directed towards valuing the non-use values of forested and
savanna ecosystems. Since in this case, the value of an ecosystem is meas-
ured in terms of its contribution to the production of other goods or serv-
ices, a relationship (or production function) must be identii ed between the
two factors. For example, if the loss of watershed protection leads to an
annual decrease in agricultural productivity worth $50, this can be imputed
as the value of the watershed for agricultural production. Kundhlande et
al. (2000) estimated the value of carbon sequestration and of water supply
for a tropical savanna-woodland ecosystem in Zimbabwe. By measuring
the standing biomass of vegetation in the region they calculated the volume
of carbon that could be sequestered by the land when forested. This value
was then compared with an estimate of the decrease in sequestration
capacity that would occur if the land-use were changed to agriculture. The
dif erence between the two amounts was then multiplied by the estimated
price of carbon to give an overall change in value of carbon sequestration
services. In this sense, the value of carbon sequestration was measured as a
function of the available biomass. In estimating the value of water in crop
production, a crop production function was used that related the amount
of crop produced to the amount of rainfall available. The value of water
was then measured as the change in crop production with changing levels
of rainfall, multiplied by the price of the crop. In addition, although not
explicitly mentioned, similar production functions were also used to dei ne
the relationships between wild foods and grass production and rainfall.
These production functions were derived by a group of biological and agri-
cultural scientists working on the project. In some cases there were docu-
mented relationships, whilst in other cases the relationships were based on
the best judgements of researchers who were familiar with the local agricul-
tural practices (W.L. Adamowicz, personal communication).
This review has shown that many studies have been carried out that
have valued a certain aspect or layer of an ecosystem's resources. It is
likely that the relative recentness of this i eld's development along with
the large amount of resources required to carry out such valuation studies
have so far precluded evaluation of entire ecosystems. However, although
no study has attempted to estimate the total economic value of an eco-
system, comparisons of the values of ecosystems under dif erent forms
