Agriculture Reference
In-Depth Information
of crop rotations, and the increasing input of synthetic fertilisers and pesticides has been
responsible for changes in the habitat of many species.
Maintaining and enhancing biodiversity is considered central to developing a sustainable
organic system. Organic farming depends upon stabilising agroecosystems, maintaining eco-
logical balances, developing biological processes to their optimum and linking agricultural
activities with the conservation of biodiversity (Alföldi et al . 2002). Increased biodiversity
improves and buffers ecological services such as pollination, pest control, maintenance of soil
fertility, thus strengthening farming systems and practices. Building on that, some organic
certification organisations have incorporated biodiversity requirements into their standards
(Alföldi et al . 2002). The Swiss organic standards, for example, require farmers to use 7% of
their land as semi-natural habitats (Bio Suisse 2001).
Tybirk et al . (2004) state that organic farming systems seem to be an appropriate tool for
planners to balance conservation and production, but the philosophy behind 'the more biodi-
versity the better' requires a deeper discussion. Many researchers have claimed that processes
and functional groups of organisms are more important for ecosystem function than 'just'
maximising the diversity (e.g. Kareiva 1994, Tilmann 1997, Hodgson et al . 1998).
In a review of 76 studies that explicitly compared the effects on biodiversity of organic
farming relative to conventional agriculture, Hole et al . (2004) highlighted three broad man-
agement practices that are largely intrinsic to organic farming (but not exclusive), and particu-
larly favour farmland wildlife: a ban or a reduced use of chemical pesticides and inorganic
fertilisers, sympathetic management of non-cropped habitats, and preservation of mixed
farming.
While comparing the impacts of organic and conventional farming systems on biodiver-
sity, Hole et al . (2004) identified the following problems:
• variation in the definition of organic farming standards between countries;
• disparity between studies in their control for extraneous variation;
• variation in the period the studies were carried out;
• variation in the spatial scale; and
• use of different 'measures' of biodiversity.
Furthermore, there are several factors that may result in underestimating the benefits of
organic farming on biodiversity, such as a possible time lag in the response of wildlife commu-
nities after switching from conventional to organic farming, or the difficulty in detecting sig-
nificant effects at the field scale for mobile taxa such as birds and butterf lies.
Nevertheless, most studies reviewed clearly demonstrate that species abundance and/ or
richness across a wide range of taxa tend to be higher on organic farms than on locally repre-
sentative conventional farms. This particularly applies to species which have experienced
declines in range and/or abundance as a consequence of past agricultural intensification.
The effects on biological diversity are reviewed in more detail for the following three
aspects: genetic diversity, species diversity (f (floral and faunal) and habitat diversity.
Genetic diersity
Today, the adoption of high yielding, uniform breeds and varieties has led to a considerable
reduction in the number of species and in the number of varieties/breeds within species used in
agriculture (Alföldi et al . 2002). There are many schemes and projects worldwide working to
conserve seed banks and indigenous varieties, many of which are linked to organic agriculture
projects (Stolton 2002). A typical example is the Sustainable Agriculture and Rural Develop-
ment Project (SARDI) in Kenya where a community indigenous seed conservation program is
being implemented. Indigenous seeds have been shown to perform better in drought conditions
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