Agriculture Reference
In-Depth Information
(Waireg 2000, reported in Stolton 2002). Another example is given by Vreeland (2000) who
reports on Indians in the High Jungle of Peru who organically cultivated cotton and thereby
conserved ecotypes adapted to the moist tropical conditions. Vreeland emphasises that native
cotton can also provide valuable genetic materials for improving commercial cotton varieties
because of the high degree of natural resistance to insects, disease and drought stress.
Even though there is evidence that organic farming systems are more likely to use rare,
native or traditional breeds, there are only few studies that investigate the role of organic live-
stock in maintaining the genetic diversity of domesticated stock (Bremond 2002).
Since 1995, organic agriculture has indirectly established a rescue process for species, vari-
eties and breeds threatened by underuse or extinction. As demonstrated in various case studies,
organic agriculture, almost without the help of governmental institutions, is providing an
important contribution to the
in
situ
conservation, restoration and maintenance of agricul-
tural biodiversity (Scialabba
et
al
. 2002).
A possible future threat to genetic diversity and biodiversity in general, could be the side
effects of the release of genetically engineered or modified organisms (GMOs) into the envi-
ronment (Soil Association 2001). In organic agriculture genetic engineering is banned (Alföldi
et
al
. 2002).
Floral diersity
In general, the diversity of f loral species is closely connected to local site conditions. Neverthe-
less, Hole
et
al
. (2004), while investigating the f flora of arable and mixed farming, recorded
higher weed abundance and species richness in fields under organic management in almost all
studies. In several studies, organically managed fields held considerably rarer and/or declining
species. However, in regions with low potential for biodiversity, the positive impact of organic
farming on wild herb or grassland diversity is less distinct (Baars
et
al
. 1983, Smeding 1992).
Factors that contribute to greater f loral diversity include the proportion of grassland
relative to arable cropping, the variation in sowing dates for cereal crops and the inclusion of
both autumn-sown and spring-sown cereals. A richer f floral diversity has positive impacts on
faunal diversity, because it offers overwintering sites, refuges and areas with network links to
other habitats (Shepherd
et
al
. 2003). Weeds are considered competitive to the crop in conven-
tional farming and are eliminated by herbicides, whereas in organic systems, some of the
accompanying plants are desired to a certain degree and are considered useful as they provide
ecological services (Alföldi
et
al
. 2002). In the context of pollinators, which greatly benefit
from a diversity of f lowers, f lowering weeds are more diverse and abundant in organic arable
fields and grassland compared to conventional fields (Frieben and Köpke 1996). In organic
grassland, the average number of species was higher than in conventional, as a result of lower
stocking rates and lower fertilisation levels in organic farms. Additionally, the mowing date is
often delayed, which means that grass species can reach the f flowering stage and thus achieve
greater reproduction, leading to plant communities rich in species and structure (Frieben and
Köpke 1996, Frieben 1997).
Van Mansvelt
et
al
. (1998) compared 7 organic and 8 adjacent conventional farms in the
Netherlands, Germany and Sweden in order to evaluate their effect on landscape diversity.
They found the farmland area dedicated to natural elements ranged from 55% to 20% in the
mixed organic farms and from 11% to 0.3% in the conventional neighbours. A study by Aude
et
al
. (2004) compared the conservation value of hedge bottom vegetation on organic and con-
ventional farms in Denmark. The hedgerows studied (28 organic, 28 conventional hedgerows)
were established in the same way except that the organic hedgerows were managed without
pesticides. Significantly more plant species were found in the organic hedgerows and their
species composition appeared similar to semi-natural plant communities.