Why do deer need such a big area for grazing?

Answer 1

Grazing by large herbivores is a major factor determining the structure and species composition of upland ecosystems. The manipulation of grazing regimes by land managers can thus be a powerful tool in the management of upland habitats. To predict the effects of unmanaged, or managed, grazing at a particular site, an understanding is needed of the foraging behaviour, diet selection and intake of the large herbivore species found in the Scottish uplands.

Answer 2

Need area because of reproducing numbers , forage competition between grazing animals and the availability of forage for big game would increase . In other words its because of other grazing animals ( competition ) and because of the reproducing of the deer.