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