pastures are not permanently planted, but alternated between fodder crops and arable crops. Rest rotation Rest rotation grazing "divides the range into at least four pastures. One pasture remains rested throughout the year and grazing is rotated amongst the residual pastures." This grazing system can be especially beneficial when using sensitive grass that requires time for rest and regrowth. Deferred rotation Deferred rotation "involves at least two pastures with one not grazed until after seed-set". By using deferred rotation, grasses can achieve maximum growth during the period when no grazing occurs. Patch-burn Patch-burn grazing burns a third of a pasture each year, no matter the size of the pasture. This burned patch attracts grazers (cattle or bison) that graze the area heavily because of the fresh grasses that grow as a result. The other patches receive little to no grazing. During the next two years the next two patches are burned consecutively, then the cycle begins anew. In this way, patches receive two years of rest and recovery from the heavy grazing. This technique results in a diversity of habitats that different prairie plants and birds can utilize—mimicking the effects of the pre-historical relationship between bison and fire, whereby bison heavily graze one area and other areas have opportunity to rest, based on the concept of pyric herbivory. The Tallgrass Prairie Preserve in northeastern Oklahoma has been patch-burn grazed with bison herds for over ten years. These efforts have effectively restored the bison–fire relationship on a large landscape scale of . In the grazed heathland of Devon, the periodic burning is known as swailing. Riparian area management Riparian area grazing is intended to improve wildlife and their habitats. It uses fencing to keep livestock off ranges near streams or water areas until after wildlife or waterfowl periods, or to limit the amount of grazing to a short period of time. Conservation grazing Conservation grazing is the use of grazing animals to help improve the biodiversity of a site. Due to their hardy nature, rare and native breeds are often used in conservation grazing. In some cases, to re-establish traditional hay meadows, cattle such as the English Longhorn and Highland are used to provide grazing. Cell grazing A form of rotational grazing using as many small paddocks as fencing allows, said to be more sustainable. Mob grazing Mob grazing is a system, said to be more sustainable, invented in 2002; it