The Structure and Dynamics of Agricultural Landscapes as Drivers of Biodiversity - Landscape Ecology for Sustainable Environment and Culture - page 291

assumption; if the number of some small, short-lived species increases with
changes in landscape composition and configuration, in the same landscapes there
is no response by longer-lived ones. The first category may perceive the landscape
at a finer spatio-temporal scale and thus react to changes that are not perceived by
the other categories. Nevertheless, even if the total number of species is not related
to the quantity of semi-natural areas, community structure changes. There is a shift
in species or in the relative abundance of species. This points out the necessity to
adapt the measure of biodiversity to the target species and to the intensity of
landscape change. Species richness is a good indicator for strong gradients of
landscape changes and for fine spatio-temporal grain species. Otherwise, some
more sensitive measures such as the composition of communities or the relative
abundance of species are needed to highlight the response of biodiversity to
landscape structure changes.
In rural landscapes, all parts of the mosaic are influenced by agricultural
activities. Even semi natural areas such as woodlots, hedgerows and even more
permanent grassland depend on the farming system. They may be sprayed by
pesticides from the crops, enriched by fertilizers from the upper fields; woodlot
boundaries and hedgerows are pruned not to shadow crops (Lotfi et al. 2010 ), etc. It
is thus an illusion to draw a strong boundary between semi-natural and productive
areas. This is shown by our work on landscapes with similar compositions and
different farming systems, with a strong response of species abundance and com-
position to changes in production type and farming practices. It is of overall
importance when comparing landscapes with different structures to explicitly
characterize farming activities. This has been done within a European project, green
veins, with 24 landscape units, distributed along a double gradient of farming
intensity and amount of semi-natural areas. The more important factor to explain
biodiversity was then the intensity of the farming system (Billeter et al. 2008 ).
14.4.2 Cropping System Mosaic
Beyond the effects of farming system intensity, our results show that the spatio-
temporal organization of crop covers, farming practices and crop rotations affect
biodiversity. Until now, this issue has mainly been addressed for crop pest species
(Carrière et al. 2006 ; Bresson et al. 2010 ; Kennedy and Storer 2010 ), but our results
on pollinators, predatory arthropods and butterflies show that the heterogeneity of
the cropping systems mosaic permits the persistence of beneficial organisms, and of
species of conservation interest. For them, the diversity of farming practices and
rotations, together with semi-natural elements, ensures habitat complementation
and/or supplementation in space and time, and determines landscape connectivity.
Over the years, crop rotations will not only control the degree of stability of
resources for species, as shown for bee communities, but also their temporal
accessibility, as illustrated by our modeling studies. Benefits of the cropping
systems mosaic are expected for species in semi-natural elements, especially in