Environmental Engineering Reference
In-Depth Information
most important. The importance of biodiversity in agriculture is well captured by
Tilman et al.
(1999
: 4) in the following words:
Humans do not produce food. Other animal and plant species produce it for us. The essence
of agriculture is the harnessing of numerous species of plants and animals for human
benefit. Many of the advances in agriculture have come from the selection and development
of new crops and from genetic refinements in these crops.
Agricultural systems benefit from the existence of a pool of genetic diversity that
serves as the primary source of new varieties. In other words, genetic diversity is
essential if a crop is to be viable over the long term. Moreover, agriculture depends
on the various plant and animal species that are grown as major sources of human
food and pharmaceuticals.
The relationship between agricultural systems and biodiversity is reciprocal,
not one-way. Agriculture, as well as other land-use systems, directly affect the
diversity of life. For example, agricultural practices have preserved some species
which would otherwise have been driven to extinction by hunting or gathering
(Tisdell
1991)
. In its policy brief, the OECD
(2005)
suggests that the Mediterranean
basis is considered a biodiversity 'hotspot', where 'hot' refers not literally to
high temperatures or warm weather, but to its high level of human-induced
agricultural biodiversity. However, agriculture has also been responsible for a
direct negative impact on biodiversity. Commercial agriculture has caused
extensive habitat loss and degradation - which are among the greatest current
and future threats to biodiversity - and it can be considered as one of the most
important causes of pollution through its excessive use of chemical inputs, irrigation
and mechanised tillage (McNeely et al.
1995
; Dirzo and Raven
2003)
. Moreover,
subsidy policies usually distort the response of agricultural producers to market
signals and prevent the efficient use and allocation of resources. Price supports
and production subsidies can contribute to increasingly intensive and polluting
agricultural practices.
The effects that agriculture has on biodiversity are 'externalities'; that is, they are
largely external to the market and thus not reflected in market prices. The fundamental
reason for this is that many biological assets, such as wild species and natural
systems, are characterized by the absence of fully defined property rights. Many of
these assets are considered to be public goods, or possess some features associated
with such goods. Pure public goods have the characteristics of non-rivalry and
non-exclusion (for example, Cornes and Sandler
1996
; Ison et al.
2002
, and many
other textbooks on environmental and ecological economics). Non-rivalry implies
that, once the good is provided to a consumer, it can be made available to other
consumers at no extra cost, or - in more prosaic, economic terms - the marginal
social cost of supplying the asset to an additional individual is zero. For example,
a nature area that is protected by or for one agent will benefit everyone else
who can access the area. Non-exclusion means that one user cannot prevent
consumption by others. Due to the non-exclusion attribute - that is, due to the
fact that it is impossible or at least very costly to deny access to a biological asset
- markets fail to allocate resources with public good characteristics efficiently.
