328 Ecological Restoration and Design
and small mammals use this habitat, as well as grassy field margins, and the inver-
tebrate and plant foods it supports (Bence et al, 1999). Some animals, such as the
hare (Lepus europaeus Pallas) and the grey partridge (Perdix perdix L.), are valued as
game species, so provide a recreational benefit as well as additional revenue for the
landholder (Boatman, 1999). Other species are of conservation significance and
include the skylark (Alauda arvensis L.) and harvest mouse (Micromys minutus (Pal-
las)). Harvest mouse nest densities on ‘beetle banks’ were 47/km compared with
only 5/km in field margins (Bence et al, 1999). Although some such species may
be rarely encountered by members of the general public, there is considerable soci-
etal benefit in the knowledge that they do still exist (‘existence value’). More tan-
gible aesthetic benefits of biodiversity are evident in the preservation of an attractive
farming landscape in which tourism and recreation can take place. Further, in
countries such as Australia, New Zealand and the US, the heritage and culture of
the aboriginal peoples has been threatened by land use practices introduced by
European settlers. Under these circumstances, the introduction of biodiversity
provides an opportunity to preserve plants of cultural significance. These may
include plants of food, fibre, ceremonial and medicinal value (Patterson, 1992;
Anon, 1994).
A contrasting, environmental benefit of enhanced vegetational biodiversity is
the prevention of soil erosion by wind and water. The vegetationally diverse ‘cor-
ridors’ that Rodenhouse et al (1992) found to enhance natural enemies of soybean
pests were considered to have the additional benefit of constituting a barrier to soil
movement. Any such effect would, in turn, help reduce eutrophication of water-
ways by minimizing inputs of nutrients such as nitrogen and phosphorus and
preserve sources of water for human use (Edwards and Abivardi, 1998).
At the ultimate spatial scale, biodiversity in agriculture can aid carbon seques-
tration (Nair, 1998). Annual carbon dioxide uptake of individual trees can be in
the order of 150kg, a benefit valued at US$5 tree/year (McPherson et al, 1999).
Conclusion
The examples outlined above illustrate that when biodiversity is increased, several
benefits may result at more than one hierarchical level, and thus multiple-function
agricultural biodiversity is achieved. Importantly, however, because of the reduc-
tionist tendency in scientific research, many of the benefits will not have been
quantified or even recognized.
Exploration of multi-function agricultural biodiversity is an important future
research theme in sustainable agriculture because many farmers will be persuaded
to conserve existing biodiversity and introduce additional biodiversity only if con-
vinced to do so by a tangible package of economically rational as well as aesthetic
benefits. Establishing the types and extents of these various benefits will demand a
greater degree of collaboration between researchers from disciplines including pest