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

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