The Structure and Dynamics of Agricultural Landscapes as Drivers of Biodiversity - Landscape Ecology for Sustainable Environment and Culture - page 294

should include a limitation of field size and soil disturbance, such as long-term
grassland and minimum tillage. The ban of herbicides in field margin management
should be part of the package.
Heterogeneity is an important variable to enhance biodiversity (Benton et al.
2003 ). In the course of this chapter we show how ''visible'' heterogeneity linked to
land cover, especially semi-natural elements and ''hidden'' heterogeneity (Vasseur
et al. in press ) resulting from farming practices play a major role to maintain high
levels of biodiversity. In Table 14.5 , we present the strengths and weaknesses of
these two approaches of biodiversity

14.5 Conclusion

To conclude we may state that until now most regulations to enhance or conserve
biodiversity have been aiming at increasing (Aviron et al. 2009 ) or managing
extensively (Kleijn et al. 2011 ) semi-natural elements. But at an era when food
production must increase to feed a growing world population it is important to
identify practices at field and landscape levels that will favor biodiversity without
retrieving land from production. One may expect a threshold of amount of semi
natural areas, 0-5 %, below which biodiversity remains low whatever the practices,
as the regional species pool will be low. Above this threshold, crop spatial heter-
ogeneity and environmentally friendly practices will increase biodiversity. For high
amounts of semi natural elements, 20 % onwards (Tscharntke et al. 2005b ), bio-
diversity will be high, even simply by keeping the current farming activities (Le-
roux et al. 2008 ). In many parts of the world, agricultural landscapes fall within the
second category. It is time to define policies that will encourage agricultural
practices and systems that maximize biodiversity for its own sake and for the
services it provides to our societies. It must also be acknowledged that all these
policies will not increase all species, but may be targeted toward certain groups.

Acknowledgments LTER research is supported by the zone atelier program of INEE-CNRS,
additional support is provided by INRA, the ministry of environment, the European Union and
the National Research Agency. We thank three anonymous reviewers for their constructive
comments.

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