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

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