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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D.II.4 Interactions between cuttings and competition (B*C)<br />
While the temporally exten<strong>de</strong>d competition will select for plant species adapted to later<br />
successional stages (K-selected species), the regular hay cuttings might have an antagonistic<br />
effect limiting the progression of successional stages (e.g. the establishment of woody species)<br />
in PFCs. There might thus be negative or positive interactions between the effects of cutting<br />
(C) and competition (B) (see <strong>de</strong>tails and references in the introduction of Article 6). Cuttings<br />
might, for example, reduce the aboveground competition for light (negative interaction) or the<br />
combination of competition and cutting may lead to disproportional reductions in weed<br />
regrowth (positive interaction). However, the measurements on small experimental plant<br />
communities in the greenhouse suggested that the negative effects of competition and cuttings<br />
were mainly additive (Article 6) and there were no signs that weed plants could profit from the<br />
temporally reduced competition after hay cuttings in the field experiment. The results rather<br />
suggested that the competitive advantage of the forage <strong>crop</strong>s appeared in particular after the<br />
first <strong>crop</strong> cuttings (see chapter C.II).<br />
D.II.5 Seed predation (D)<br />
Weed seed predation is an ecological interaction between plants and animals that is not<br />
frequently investigated in agro-ecosystems, although recent studies suggested i) that weed<br />
seeds are an important food resource in arable fields (Manson and Stiles, 1998; Wilson et al.,<br />
1999; Kollmann and Bassin, 2001) and ii) that seed predation may have strong impacts on<br />
weed population dynamics (Menalled et al., 2000; Davis and Liebman, 2003; Westerman et<br />
al., 2003c; Mauchline et al., 2005). High predation rates observed in Articles 6-8 (about 30-<br />
80% of presented seeds were eaten during one or two weeks) support these two hypotheses.<br />
Weed seed predation may thus contribute to alleviate the ‘weed tra<strong>de</strong>-off’.<br />
A priori, weed seed predation may take place in any <strong>crop</strong>. However, it may be of particular<br />
importance in perennial <strong>crop</strong>s and field margin strips for two reasons: 1) Soil tillage does not<br />
burry newly produced weed seeds into the soil, therefore, more seeds will stay exposed on the<br />
soil surface during the whole duration of the <strong>crop</strong>, thus for several years. (However, seeds may<br />
also be buried by animals). 2) The absence of soil tillage and the permanent vegetation cover<br />
may constitute a more stable habitat compared to annual <strong>crop</strong>s that might favour the presence<br />
of different seed predators (Cromar et al., 1999; Van Klinken, 2005). The field experiments in<br />
2008 suggested that (i) weed seed predation rates in perennial forage <strong>crop</strong>s are as high as in<br />
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