Diversifying crop rotations with temporary grasslands - Université de ...
Diversifying crop rotations with temporary grasslands - Université de ...
Diversifying crop rotations with temporary grasslands - Université de ...
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
<strong>crop</strong>s (Clay and Aguilar, 1998; Cardina et al., 2002a; Teasdale et al., 2004) and mown field<br />
margin strips (De Cauwer et al., 2005). However, other previous studies reported reduced<br />
abundances of (annual) grass species including Apera spica-venti (L.)P.Beauv., Avena fatua L.<br />
and Setaria sp. (Norris and Ayres, 1991; Gill and Holmes, 1997; Schoofs and Entz, 2000;<br />
Cardina et al., 2002a; Albrecht, 2005) while the perennial grasses Elymus repens (L.) Gould<br />
and Poa sp. sometimes profited from perennial <strong>crop</strong>s (An<strong>de</strong>rsson and Milberg, 1996; Clay and<br />
Aguilar, 1998; Teasdale et al., 2004; Albrecht, 2005). Heterogeneous reactions of different<br />
grass species might be due to two opposed effects: most grasses probably have a good<br />
vegetative regrowth capacity (see chapter C.III), but hay cuttings may consi<strong>de</strong>rably reduce<br />
seed production of grassy weeds, especially all grass species that have tall and upright<br />
reproductive spires, which was also observed by Dalbies-Dulout and Dore (2001) for A.<br />
myosuroi<strong>de</strong>s in mown set-asi<strong>de</strong> fields. Therefore, grasses may sometimes have high biomasses<br />
in perennial forage <strong>crop</strong>s but this does not necessarily lead to high seed production and<br />
increasing populations (see chapter C.II). The success of seed production thus <strong>de</strong>pends on the<br />
species’ phenology and the exact cutting dates.<br />
D.I.6 Weed abundance and diversity<br />
While the community composition varied strongly between annual and perennial <strong>crop</strong>s, and<br />
during the <strong>crop</strong> rotation of the space-for-time substitution <strong>de</strong>sign, variations in species<br />
diversity were smaller. At the field scale, higher species diversities were observed only for<br />
young perennial <strong>crop</strong>s (Fig. 2 of Article 2), when species typical for annual and perennial<br />
<strong>crop</strong>s co-existed temporally. This corresponds to the field experiments, where plant diversities<br />
were highest during the first month of the perennial <strong>crop</strong>s (Fig. 12). Afterwards, weed<br />
diversities <strong>de</strong>creased at the field scale <strong>with</strong> the age of the perennial <strong>crop</strong>s in both the large and<br />
the small-scale studies (which was mainly due to the reduction of typical arable weeds).<br />
Interestingly, these <strong>de</strong>creases were less strong than the <strong>de</strong>crease in weed abundances,<br />
improving the richness/abundance ratios compared to annual <strong>crop</strong>s (Fig. 12). Moreover, the βdiversity<br />
(dissimilarity between the fields in the large-scale surveys) remained high (Fig. 2 of<br />
Article 2).<br />
Sjursen (2001) observed a similar <strong>de</strong>crease in weed species numbers (and weed abundance) in<br />
the established vegetation during 3-year forage <strong>crop</strong>s. In this study, Sjursen (2001) observed<br />
reduced weed abundances in the soil seed bank, but species diversities remained unchanged in<br />
the soil. In long-term experimental studies conducted by Sosnoskie et al. (2006), seed bank<br />
160