The Structure and Dynamics of Agricultural Landscapes as Drivers of Biodiversity - Landscape Ecology for Sustainable Environment and Culture - page 278

of landscape structure, which is defined in this study by the proportion of semi-
natural elements, on biodiversity measured with several taxa differing by their way
of dispersal and their spatial scale of perception.
It soon appeared that biodiversity responses to this heterogeneity could be
linked to farming systems, as it was proved that farming practices also played a
major role in the decline of biodiversity. To assess this at the landscape level we
compared landscape units, first with similar agricultural systems and contrasted
landscape structures, and second, of similar landscape structure and contrasted
farming systems.

14.2.1 Comparing Landscapes with Contrasted
Landscape Structures

In Brittany, France, as in most places of north western Europe, agricultural
landscapes changed dramatically in the 1960s and up to 1980s due to the rapid
intensification of agriculture (Robinson and Sutherland 2002 ). This led to an
important decrease in semi natural habitats (Meeus 1993 ). To assess the effects of
these changes on biodiversity we compared the gamma diversity of landscapes that
differed by their amount of semi natural elements and where agricultural systems
were similar.
The study area, the Long Term Ecological Research (LTER) site ''zone atelier
Armorique'', is located in northern Brittany, south of the Mont Saint Michel Bay,
France (48 36 0 N, 1 32 0 W). A hedgerow network (bocage) characterizes the
landscape and agriculture is oriented toward milk production. Three units differing
by field size, the density of the hedgerow network, and the relative abundance of
grassland versus cropland have been delineated (Fig. 14.1 ). We used global
indices such as percentage cover of woodlots, grasslands, crops, hedgerows, het-
erogeneity (Baudry and Burel 1982 ) to verify that units are different and have
some kind of internal homogeneity (Table 14.1 ).
We surveyed several groups of organisms which perceive the landscape at
different spatial scales, and have different ways of dispersal and different life

(a) (b) (c)

Fig. 14.1 Parts of the three landscape units: the quantity of semi natural areas: woodlots,
hedgerows and permanent grassland, decreases from (a)to(b) and (c) as stated in Table 14.1