The Structure and Dynamics of Agricultural Landscapes as Drivers of Biodiversity - Landscape Ecology for Sustainable Environment and Culture - page 281

sampled per site during the summer of 2001. We compared carabid species
composition between the two ''cropland'' groups. They were characterized by two
distinct clusters of species, maize-dominated landscapes hosted species occurring
in rather moist and shaded habitats such as Brachinus scolopeta, while cereal-
dominated landscapes hosted typical crop field species such as Pterostichus
melanarius.
The abundance of carabids significantly differed between the two types of
landscapes (t = 5,82, p = 0.01). The average abundance was 693 individuals per
site in the cereal-dominated landscapes, and 333 for the maize-dominated ones.
Species assemblages of the most different sites were compared using the ten most
abundant species found at each site. These top ten species accounted for
81.6-87.8 % of the total catch, depending on the site. The top ten species present
in the maize-dominated landscapes only accounted for 13.7 % in the cereal-
dominated ones, reflecting the strong effect of this shift in farming system and
change in landscape configuration (Table 14.3 ).
These results show that farming systems have an effect on biodiversity at the
landscape scale. The effects of farming systems on biodiversity have mainly been
studied for comparisons between conventional and organic systems and looking at
the effect of the surrounding landscape on alpha diversity (Weibull et al. 2000 ;
Purtauf et al. 2005 ). The main results are that diversity is higher in complex
landscapes with a high proportion of semi natural areas whatever the system, and
that organic systems enhance diversity in simple landscapes. Our results deal with
gamma diversity and systems that are both conventional but with different crop
and husbandry productions. They are intensive agricultural systems, but the one
dominated by maize and milk production is less favorable for carabid species than
the one dominated by cereal crops. This may be due to the differences in farming
practices, with higher inputs in maize fields, or to the configuration of the land-
scape with larger fields and a lower connectivity of the hedgerow network when
maize is dominant.

Table 14.3 Abundance of the top ten carabid species in the most different landscape units of the
two types: maize and cereal dominated

Cereal dominated
landscape

Maize dominated
landscape

Pterostichus madidus (Fabr.) 19 6

Nebria brevicollis (Fabr.) 89 6

Abax parallelepipedus (Piller and Mitterpacher) 0 19

Calathus piceus (Marsham) 81 1

Amaras pp. 28 55

Harpalus rufipes (De Geer) 122 0

Pterostichus melanarius (Illiger) 72 1

Poecilus versicolor (Sturm) 2 3

Agonum dorsale (Pontoppidan) 15 79

Poecilus cupreus (L.) 3 12