A modelling approach to assess trade-offs between ecological and productive outcomes in livestock farming system
Résumé
The impact of cattle trampling on grassland birds is all the more important since bird nest during months with highest grass growth. Therefore management prescriptions aim at limiting stocking rate during spring. However it is still unclear to what extent these thresholds on stocking rate reduce productive performance. Based on a model linking grazing strategies and dynamics of two bird species we developed a cost effectiveness approach to assess ecological and productive outcomes of environmental friendly policies for a large range of stocking rate constraints (SRC). The absence of SRC over 15 years led bird populations close to extinction for both species while ensured optimal productive performance. Moderate level of SRC limited productive performance by 15% and avoided bird extinction with unequal outcomes for each species (respectively 37% and 62% of initial population size). Highest levels of SRC reduced productive performance by 25% with minor decline of wader populations. These good performances on both economic and ecological viewpoints can be explained by deferred grazing. A maximal economic performance seems to be sorely compatible with ecological outcomes. These results could be used to design management compensations based on the level of constraints imposed on the livestock farming system.