GRAZING ECOLOGY AND THE CONSERVATION OF HEATHER MOORLAND - THE DEVELOPMENT OF MODELS AS AIDS TO MANAGEMENT

Loss of heather has occurred as a result of overgrazing by sheep. There is a clear need to develop grazing management protocols to sustain heather. Most areas of heather moorland contain a mosaic of four or more vegetation types, with the precise proportion by area of each vegetation type as well as patch size, shape and distribution being unique to each moor. The vegetation types differ in their dry matter production, feeding value and attractiveness to grazing sheep and other herbivores. The unique nature of the vegetation mosaic on each moor has important consequences for management. In the case of sheep farming, both the impact of the animals on the vegetation and the carrying capacity of a moor for sheep production will vary depending on the vegetational composition. The prescription of a single stocking rate for use on all grazing units containing heather is not sensible in these circumstances. Our knowledge and understanding of the biology of the moorland grazing system, however, has reached the stage where information on the productivity and feeding value of the various vegetation types and on foraging behaviour and diet selection of the sheep is sufficient to build computer models. These models allow examination of different management options. An early model currently allows the determination of the upper limits to stock numbers for year-round grazing systems on particular moors if damage to heather is to be avoided. A more complex model is being developed which will allow examination of the effects of different seasonal patterns and levels of stocking on the offtake levels from the various vegetation types on a particular moor, and on the quality and quantity of the sheep's diet. This model is still being developed and validated, but it provides a promising tool with which to explore management options. Extension of the latter model to include other species of grazer and the effect of different patterns of vegetation is needed to develop multiple land-use models or prescriptions to obtain the optimum biological and economic balance.