Structure and dynamics of grazed vegetation

摘要

The relationship between vegetation and grazing herbivores is dynamic; the structure and quality of vegetation affect the diet of grazing herbivores and, in turn, the components of grazing (defoliation, excretal return and treading) affect the structure and species composition of the vegetation. Both the vertical and horizontal distribution of vegetation are important in understanding plant-animal interactions in grazed plant communities. Mechanisms which confer grazing resistance, through avoidance and tolerance strategies, are discussed. The difficulties in addressing scaling issues at the plant-animal interface are addressed; measurements or events at a small scale cannot be directly extrapolated to a larger scale. Moreover, integration of small-scale functions could result in counter intuitive results at the larger scale. The role of modelling in exploring spatio-temporal heterogeneity in plant-animal interactions is developed. Such models allow the exploration of a large number of hypotheses which cannot be tested under experimental conditions because of logistical, time and money constraints, and provide a framework in which to better understand grazing systems. As a management tool, models have value in their predictive capacity and ability to simulate the complex situations in grazed plant communities.