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

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