PARENT SESSION
Poster Session 7: Grasslands
Tuesday, August 9, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal
Modelling the potential impact of sheep's grazing on dominant shrub (Scotch broom) population dynamics.
Chambon-Dubreuil, Estelle*,1, Magda, Danièle 1, Jarry, Marc2, 1 INRA-SAD Arche / Sicomor, Toulouse, France2 UMR INRA/UPPA ECOBIOP, IBEAS-UPPA, Pau, France
ABSTRACT- The European natural rangelands are attracting attention because of their environmental value as habitats for threatened fauna and flora species and the diversity of landscapes. Those responsible for the implementation of the European agri-environmental policy are hence encouraging livestock farmers to adopt grazing practices that contribute to limiting encroachment by dominant shrubs, but not to eliminate them, since most of them contribute to structuring habitats of protected species. This paper rests on an interdisciplinary study on interactions between small ruminant's feeding strategy and population dynamics of dominant shrubs with the objective of modelling impact of grazing on the structure of population and their demography. Our main goal is to test the potential impact of grazing on Scotch broom population at different phenological stages. Concerning the ruminant's feeding strategy, we rest on recent researches which allowed acceding to the foraging behaviour in response to variable feeds on offer. In order to analyse the demographic strategy of the dominant plant population, recording of the different demographic parameters of the dynamics of broom populations (germination, dormant rate, fecundity and survival rate) were carried out on an ungrazed shrubland. A grazing experiment with sheep was conducted at different phenological stages to identify the edible plant parts and quantify their consumption rate. The demography was studied using a classical life cycle graph including categories defined to their response to grazing, and modelled using projective matrices. Our experiments shows that several plant parts of broom are consumed (flower, pods, shoots and stems) offering multiple potential demographic interactions on accessible adults. A major response of repeated grazing was the process of adults bushes becoming vegetative and then creating a new demographic category within the population structure. The parameter estimation was conducted from these experiments were performed from 2002. The model we present here is based on this new life cycle graph and permit to simulate the potential grazing impact at different phenological stages. Simulations of potential grazing impact at different seasons pointed out the importance of the role of vegetative adults and mortality of juveniles.
Key words: Ecological modelling, Dominant species, Grazing, Matrix model