Agriculture Reference
In-Depth Information
affect beneficial arthropods. But the toxicity of natural pesticides is usually lower and their
degradation significantly faster in comparison to synthetic pesticides (DEPA 1998, UNCTAD
2003). Additionally, the higher fertilisation levels in conventional fields lead to a greater density
of crops, which can alter the microclimate and can also reduce the occurrence of species
dependent on a warm microclimate and on light (Pfiffner and Niggli 1996, Pfiffner and Luka
1999). Jauset
et
al
. (2000) demonstrated that tomato plants fertilised with high nitrogen (N)
levels showed a higher intrinsic rate of increase of greenhouse whitef ly populations. Yardim
and Edwards (2003) studied the effects of organic and synthetic fertilisers on pests (aphids)
and predatory arthropods associated with tomatoes. The application of both organic and syn-
thetic fertilisers could increase pest populations. However, they found lower populations of
aphids on organically fertilised tomatoes after one year, indicating that organic fertilisers may
have the potential to reduce pest attacks in the long term.
In Europe, researchers have found greater diversity and abundance of soil and surface-
living arthropods such as spiders, beetles, parasitic f lies and wasps as well as non-pest butter-
f flies, and many other invertebrate species in organic farming systems compared to conventional
farming systems (Feber
et
al
. 1997 1998, Pfiffner and Mäder 1997, Kromp1999, Stolze
et
al
.
2000, Sunderland and Samu 2000, Tybrik
et
al
. 2004). However, some reports have not found
these differences to be as clear (Gardner and Brown 1998), and in the case of aphids, there are
generally fewer present in organic fields (Reddersen 1997). Berry
et
al
. (1996) examined the
abundance and ecological diversity of selected groups of beneficial arthropods on 16 organic
and 17 conventional carrot fields in New Zealand. The organic fields had significantly higher
numbers of Hymenoptera and Neuroptera as well as a significantly more diverse predatory
and parasitic community than the conventional fields.
Birds
The decline in farmland bird populations is well documented. Birds are well-suited indicator
organisms that show the environmental status of nature and landscape infrastructure including
agricultural land. Several studies show that bird densities are higher in organic farms. A study by
Rhône-Poulenc (1997) has shown a steady annual increase in the number of bird territories on
land converted to organic production and a larger overall number of territories on organically
managed land. The British Trust for Ornithology (1995) found that breeding densities of skylarks
and densities of birds in general were significantly higher on organic farms. In coffee production
in Latin America, another factor appears more important - research carried out by the Smithso-
nian Migratory Bird Centre in Colombia and Mexico showed more than 90% fewer bird species
in sun-grown coffee plantations as opposed to shade-grown coffee (Alger 1998). Shade-grown
practices are recommended in organic standards as they fulfil requirements to enhance soil fer-
tility, pest and disease control and expand crop production options (Rice and Ward 1996). While
many interactions between organic farming and biodiversity are positive, some actions can have
a negative impact, particularly on ground-nesting birds. These include mechanical weeding,
mulching operations, certain mowing techniques and timing of operations (Jones
et
al
. 1996,
Fuller 1997, Welsh
et
al
. 2002, Shepherd
et
al
. 2003, Reiter and Krug 2003).
Mammals
According to Hole
et
al
. (2005), there are only two strictly comparative studies of organic and
conventional farming and their inf luence on mammalian biodiversity. Brown (1999) found
that activity levels of small mammals (wood mouse, bank vole, common shrew) were greater
in organic than conventional fields. Increased food abundance through hedgerows and field-
edge habitats was cited as the most significant factor that benefitted these and a range of other
mammalian species occurring on farmland. Many small mammal species are likely to have
been affected by reduced insect and weed-seed food resources resulting from intensification
