Diversifying crop rotations with temporary grasslands - Université de ...

Weed seed predation may increase farmland biodiversity as weed seeds constitute an
important trophic resource for various animals such as birds, micro-mammals, beetles, ants,
slugs, crickets, worms and even isopods, including several endangered species (Wilson et al.,
1999; Kollmann and Bassin, 2001; Saska, 2008). Compared to other plant tissues, seeds have
relatively high energy contents and may be available during unfavourable seasons (winter)
when other plant or insect food items are scarce (Wilson et al., 1999; Vickery et al., 2001;
Holland et al., 2006). For the plant populations, seed
predation may reduce the density of seed
banks, hence the density of weed emergence in future crops, especially for annual weed
species, which are entirely dependent on generative reproduction. This may be beneficial for
crop production and may decrease the need for curative weed control such as herbicide
applications. Several recent papers based on field experiments (Davis and Liebman, 2003;
Westerman et al., 2003c) and modelling (Jordan et al., 1995; Davis et al., 2004; Kauffman
and Maron, 2006) suggest potentially strong impacts of seed predation on weed population
demography. For example, Westerman et al. (2005) showed that a seed loss rate of 40% per
year would be sufficient for stabilizing Abutilon theophrasti population densities in a system
with low herbicide inputs. Weed seed predation may therefore be considered a ‘biological
weed control’ (Hatcher and Melander, 2003; Westerman et al., 2005; , 2006).
A.III.6 Integration or spatial separation of farming and biodiversity?
Two strategies have been proposed for combining crop production and biodiversity
conservation. ‘Wildlife friendly farming’ intends to integrate both at the same location
whereas ‘land sparing’ intends to separate them spatially (Balmford et al., 2005; Green et al.,
2005; Mattison and Norris, 2005). Green et al. (2005) argued that ‘wildlife friendly farming’
should be preferred if the relationship between productivity (crop yield) and biodiversity
(wildlife population densities) is convex (high gain of biodiversity for small yield reductions).
Conversely, ‘land sparing’ should be preferred if the relationship is concave (only small gains
of biodiversity for the same yield reduction). However, the shape of this relationship is
difficult to determine in practice.
In parallel to these theoretical considerations, both strategies may have several other
advantages and shortcomings (summarized in Table 3). The ‘land sparing’ strategy may e.g.
be more adapted to preserve natural areas with ‘wild’ habitats and associated plant and animal
communities while ‘wildlife friendly farming’ may be more adapted for preserving typical
farmland species and traditional cultural landscapes (van Elsen, 2000; Matson and Vitousek,
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