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.I.5 Functional groups<br />
The different analyses based on the large-scale weed surveys on commercial fields, the field<br />
and greenhouse experiments suggest that the species suppressed and favoured by PFCs may<br />
be grouped into functional groups according to plant taxonomy, morphology and life cycle.<br />
D.I.5.1 Annual vs. perennial weed species<br />
Results from the different studies suggest that perennial forage <strong>crop</strong>s favoured perennial over<br />
annual species (see Article 3 for some perennial weed species such as Cirsium arvense that<br />
did not follow this pattern). This has already been reported in previous studies (Ominski et al.,<br />
1999; Albrecht, 2005; Hiltbrunner et al., 2008) and agrees <strong>with</strong> ecological succession theory.<br />
Several mechanisms might be at the origin of this observation: (i) the absence of soil tillage<br />
may especially benefit species <strong>with</strong> longer life cycles, (ii) perennial species might be better<br />
adapted to temporally exten<strong>de</strong>d competition and (iii) to frequent hay cuttings than annuals (see<br />
<strong>de</strong>tails in the discussion on the mechanisms in chapter D.II below).<br />
D.I.5.2 Small vs. tall or climbing species<br />
Results from the different studies suggest that perennial forage <strong>crop</strong>s suppressed in particular<br />
species <strong>with</strong> an upright and climbing broad-leaved species such as M. annua, C. album, F.<br />
convolvulus and G. aparine) compared to creeping species <strong>with</strong> a small height or <strong>with</strong><br />
rosettes. This result corresponds to previous experimental studies, where forage <strong>crop</strong>s<br />
suppressed broad-leaved weed species <strong>with</strong> similar upright or climbing morphologies such as<br />
Abutilon theophrasti Medik., Amaranthus sp., and sometimes even the same species such as<br />
C. album and G. aparine (Teasdale et al., 2004; Albrecht, 2005; Heggenstaller and Liebman,<br />
2006). Lian et al. (2006) observed that periodic cutting operations (each 2 month) suppressed<br />
the dominance of a climbing exotic weed in Chinese ecosystems, Mikania micrantha H.B.K<br />
and promoted the growth of native and other exotic species, mainly from the Alteraceae<br />
family, where rosettes are wi<strong>de</strong>spread.<br />
D.I.5.3 Grasses vs. broadleaved species<br />
While grasses showed higher survival rates and quicker regrowth after cutting compared to<br />
broadleaved species in the greenhouse experiments on individual plants, the whole group of<br />
grasses did not show increased frequencies and abundances neither in the large-scale weed<br />
surveys nor in the field experiment. This is in contrast to some previous studies in perennial<br />
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