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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diversity (α-diversity). Due to the strong differences in species composition between annual<br />
and perennial <strong>crop</strong>s exceeding the difference among annual <strong>crop</strong>s, plant diversity will also be<br />
increased at the <strong>crop</strong> rotation level (corresponding to a ‘temporal β-diversity’) and therefore<br />
probably also at the landscape level.<br />
Another feature of this research project is that a significant effort was <strong>de</strong>voted to analytical<br />
studies aimed at gaining more knowledge about the processes involved in the impacts of<br />
PFCs. Two processes were scrutinized by specific experiments:<br />
• The dynamic post-cutting regrowth process of weeds and <strong>crop</strong>s was clearly a major<br />
process to analyse. The first cuttings often drastically changed ratios between <strong>crop</strong> and<br />
weed biomass in the field experiment. The greenhouse experiments conducted on<br />
individual plants and small experimental communities did in<strong>de</strong>ed <strong>de</strong>monstrate huge<br />
differences in post-cutting regrowth abilities between weed and cultivated species,<br />
explaining the effects of cuttings on the changes in speceis composition. Interestingly, the<br />
experiments also provi<strong>de</strong>d insights about other factors affecting post-cutting regrowth,<br />
namely the phenological stage and the plant biomass at cutting, and also the cumulative<br />
number of previous <strong>de</strong>foliations.<br />
• The second investigated mechanism was weed seed predation, a process currently gaining<br />
much attention in the agroecology research community. Weed seeds are an important<br />
trophic ressource for various farmland animals all year round, and seed predation might<br />
contribute significantly to weed control. The experiments confirmed that seed predation<br />
could be quantitatively important, but also highly variable across species, seasons, and<br />
environmental conditions. Correlations observed between the level of seed predation and<br />
vegetation cover provi<strong>de</strong>d an early interpretation of the observed variability, but the<br />
question of weed seed predation opens a huge research area that needs to be further<br />
investigated.<br />
Integrating large-scale analyses <strong>with</strong> fine-scale experimentations was a goal of the research<br />
program from its inception. This was sometimes exhausting to manage, but it helped building<br />
an consistant scheme. The large-scale analysis based on a big dataset from the collaborative<br />
research project ECOGER allowed the study of the effects of PFCs on weed communities and<br />
statistically <strong>de</strong>monstrating their impacts <strong>de</strong>spite a high diversity of situations in terms of<br />
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