Spatial heterogeneity and grazing processes

Large-scale spatial patterns, whether in the height, density, or species composition of vegetation, are one of the most demonstrable and widely recognised features of heterogeneity in large herbivore grazing systems. But to understand how their existence relates to grazing processes, and what the implications of the patterns are for plants, animals, and for land users, requires adding spatial concepts, and dynamics to our knowledge of the interactions between plants and animals. Neither approach has been traditional in agricultural research. In this paper, we provide an overview of what we propose are some of the key topics and questions that arise in attempts to understand spatial aspects of the interaction between plant growth (food resources) and animals' behaviour. Rather than review advances in any one area in detail, we look at some basic principles of the fundamentally different ways in which animals eating from vegetation (with or without selectivity) affect the components of plant regrowth; the variance about these; the way this 'seeds' the creation and maintenance of heterogeneity, and most important the outcome (intake) for the animals. Likewise we outline some basic features of animals' behaviour, given heterogeneous and so spatially distributed food, which includes the expected rates of encounter; learning and memory; and both the benefits and costs of social interactions when foraging as a group. In this way we combine knowledge from several disciplines (plant physiology; animal science; behavioural ecology and not least from practical agriculture) with a goal of providing a basis for the development of simple pragmatic means for manipulating a grazed but multipurpose landscape to balance diversity, heterogeneity and agricultural performance.