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

the simulation model, although increasing the complexity of models increases the risk for
over-parameterization, which may reduce the predictive robustness.
Such mechanistic models (‘ALOMYSYS’ and ‘GENESYS’) have been developed by the
weed research group (BGA) in Dijon (France). The ALOMYSYS model simulates the
population dynamics of Alopecurus myosuroides as affected by cropping systems, and
GENESYS is dedicated to the population dynamics and gene flow at the landscape level
between different wild and cultivated rapeseed (Brassica napus) and beet (Beta vulgaris)
varieties (Colbach et al., 2006a; Colbach et al., 2006b; Colbach et al., 2007; Sester et al.,
2008). FLORSYS is a new model currently under development 19
using basically the same
principles, but simulating the dynamic of the whole plant community (several weed species
and the crop), hence accounting for the differences in weed traits across the species, and for
their contrasted response to cropping systems (Gardarin et al., 2007a).
The models simulate the plant life cycle, representing the state of the system with a daily time
step, and the various biological and physical processes affecting seed germination, seedling
emergence, seedling growth and development, plant mortality and seed production (Colbach
et al., 2007). Most processes involved in weed population and community dynamics may
already be simulated by the plurispecific FLORSYS model, including the impacts of soil
tillage (types and dates) on seed distribution within the different soil layers, the effects of soil
temperature and humidity on seed germination, the effects of herbicides on weed mortality,
and competition with neighbouring crop and weed plants. However, the current versions of all
three models account neither for losses of weed seeds due to predation nor for processes
specific to perennial crops, e.g. the impacts of repeated hay cuttings on weed and crop growth.
In the current versions, the life cycle of all weed plants is interrupted at soil tillage after crop
harvest. Therefore, cropping systems including perennial crops cannot be simulated. The
existing models must thus be extended with additional modules that simulate (i) the regrowth
abilities of weed and crop plants after repeated cuttings and (ii) the impacts of seed predation.
Knowledge obtained from this thesis might be used for supporting model construction of postcutting
weed and crop growth (see below). However, additional studies on weed seed
predation are probably required before this complex ecological interaction between plants and
animals can be formalized in a mechanistic way.
19 http://www2.dijon.inra.fr/bga/umrbga/spip.php?article151 (accessed on 21 April 2010)
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