The Structure and Dynamics of Agricultural Landscapes as Drivers of Biodiversity - Landscape Ecology for Sustainable Environment and Culture - page 280

are relatively more abundant in dense hedgerow network landscapes, while crop
species such as the Field vole (Microtus agrestis) are more abundant in sparse
ones.
In these bocage landscapes, differing by the proportion of semi natural areas the
response of biodiversity varies according to the different groups. For some of
them, the high proportion of semi natural areas leads to an increase in species
richness which has been shown in other studies for several taxa (Weibull et al.
2000 ; Schweiger et al. 2005 ). But according to dispersal ability and longevity of
species not all of them react that way. This may be due to the fact that the gradient
of landscape structure is not very long, the total proportion of semi natural areas
varying only from 25 to 45 % of the total area, contrary to other studies where it
may vary from 10 up to 80 % (Gabriel et al. 2005 ). Our results emphasize that
species richness per se is not always a good indicator for measuring a community's
response to landscape changes. Similarity indices or relative abundance permit to
identify changes in biodiversity even when species richness remains the same.
Those indices underline that different groups react differently to the same changes
in landscape structure. Nevertheless, for all of them the proportion of semi natural
elements had an effect on the structure of the communities.

14.2.2 Comparing Landscapes with Similar Compositions
and Contrasted Farming Systems

To assess the role of farming systems at the landscape level we compared biodi-
versity among landscape units of similar landscape structure but contrasted

farming systems.
We studied landscapes located in the Côtes d'Armor, an administrative unit
located in the northern part of the Brittany region. Its area is 700,000 ha, 440,000
of which are devoted to agriculture. It is a very dynamic agricultural area spe-
cialized in both milk production and hogs and poultry indoor production. Crops
sustain mainly husbandry with maize and grassland for cows, and cereals for hogs
and poultry ( http://draaf.bretagne.agriculture.gouv.fr/Les-Cotes-d-Armor,203 ).
We first selected 11 landscape units which represented the whole diversity of the
landscape structures present in the area. They differ by their composition, total
length of hedgerows, connectivity of the hedgerow network and heterogeneity of
the mosaic. Carabid beetles have been surveyed in order to measure their gamma
diversity in hedgerows and we tested for the influence of landscape structure and
farming systems on it (Millan-Pena et al. 2003 ). We then compared sites domi-
nated by cropland, which we split into two groups. They were both characterized
by a low proportion of semi natural areas, were similar in landscape composition
but differed in landscape configuration. The first one was characterized by large
fields, with maize as the dominant crop and a low connectivity of the hedgerow
network, while the second was characterized by smaller fields, with wheat and oat
as dominant crops and a more connected hedgerow network. Ten hedgerows were