Agriculture Reference
In-Depth Information
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encourage the return of more varied insects, which would provide more
predators for crop pests.
Biodiversity includes all species, and one concern has been the declining
numbers of birds within agricultural landscapes. Bird surveys on four types
of neighboring land uses were conducted: conventional, minimum-tillage,
organic, and wild land (Shutler et al. 2000). Not surprisingly, wild lands
are superior to any agricultural landscapes in terms of bird habitat, but
within the agricultural lands, the presence of wetlands was most beneficial
to bird occurrence, and organic farms had more such lands. Otherwise,
minimum tillage was found to provide cover that increased bird presence.
Organic farms had more hedgerows that act as corridors and habitat for
bird species. Overall, it is difficult to draw conclusions by focusing solely
on separate farm fields; rather, the entire landscape must be studied to
understand the effects of farms and the surrounding land uses.
Agricultural fields and field edges in England and Wales were studied
over three breeding seasons for birds (Chamberlain et al. 1999). Eight of 18
species were at a significantly higher density on organic field boundaries
than on conventional fields. Organic farms tended to provide a landscape
more conducive to bird mating and habitat: more trees, smaller field size,
and wider hedges. Even when hedgerows are present on various types of
farms, researchers have found that higher vegetative species diversity is
associated with hedgerows on organic farms (Aude et al. 2003). Apparently,
pesticide applications on conventional farms affect their nearby hedgerows
and kill some of the vegetation there as well. But hedgerows on organic
farms have more diverse vegetation, which provides more habitat to attract
more varieties of animal life.
Rather than looking at the birds themselves, one study investigated the
abundance of centipedes as an indicator of bird diets (Blackburn andArthur
2001). The authors believe that by studying the food supply, we can better
understand the decline of birds in agricultural areas. Samples were gathered
from crop field edges and adjoining woodlands from twelve pairs of organic
and conventional farms in England and Wales. Species richness and diver-
sity were actually similar between the two types of farms, but the overall
density of centipedes was much higher within the organic field margins.
This indicates that there was a modest overall reduction in centipedes on
conventional farm fields, which would not be obvious in smaller sample
studies. This decline probably was not apparent to farmers or other ru-
ral residents either, since the overall reduction was moderate and uniform
among all types of centipedes (or bugs in general). Pesticides acted to di-
minish the population of bugs, but did not wipe them out completely - that
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