Still further to the north, the steep fellsides above the Inlier are unenclosed and grazed exclusively by sheep. In the past this would perhaps be best described as "ranching" as, in the summer the sheep would range freely over the top of the Pennine escarpment and down into Teesdale. Regular "gathers" would be held to round them up for dipping and shearing. Much has changed in this respect, however, since the catastrophic foot-and-mouth outbreak of 2001. The "hefted" herds which had previously acquired a useful territorial instinct were all lost and are now only slowly being replaced. The old "commoner" system, whereby grazing (and other) rights were granted exclusively to individuals, has also been bought out by English Nature, concerned about the effect of over-grazing. Sheep numbers are now closely controlled. English Nature is also attempting to develop the diversity of the fell side habitat and has planted selected areas with hardy indigenous species such as juniper. A particular aim is to re-introduce the black grouse to the area.