Structure and dynamics of grazed vegetation

The relationship between vegetation and grazing herbivores is dynamic; the structure and quality of vegetation affect the diet of grazing herbivores a nd; in turn, the components of grazing (defoliation, excretal return and tr eading) affect the structure and species composition of the vegetation Both the vertical and horizontal distribution of vegetation are important in un derstanding plant-animal interactions in grazed plant communities. Mechanis ms which confer grazing resistance, through avoidance and tolerance strateg ies, are discussed. The difficulties in addressing scaling issues at the pl ant-animal interface are addressed; measurements or events at a small scale cannot be directly extrapolated to a larger scale. Moreover, integration o f small-scale functions could result in counter intuitive results at the la rger scale. The role of modelling in exploring spatio-temporal heterogeneit y in plant-animal interactions is developed. Such models allow the explorat ion of a large number of hypotheses which cannot be tested under experiment al conditions because of logistical, time and money constraints, and provid e a framework in which to better understand grazing systems. As a managemen t tool, models have value in their predictive capacity and ability to simul ate the complex situations in grazed plant communities. (C) Elsevier/Inra.