Grazing: too much, too little?

We are all familiar with the many of the animals which graze our uplands. They include domestic livestock, for example sheep and cattle, and wild herbivores such as red deer and mountain hares.

Some plants, for example soft grasses and herbs, are very palatable and favoured by grazing animals. Others are tough and tend to be avoided. If an area is grazed heavily then the attractive species can be eaten out, either directly or through not being able to set seed, and the less palatable ones expand to fill the gaps. This benefits neither the habitat, the insects etc which rely on the lost species, nor indeed the grazers themselves.

Still other plants, such as heather, although perhaps not instantly obvious as attractive to grazing (or browsing) animals, have the advantage that they do not die back in the winter. Heather is thus an important source of winter food for deer, sheep etc. Its young shoots are also an essential food for red grouse. However, if too much of a heather plant is eaten on a regular basis it will eventually die. This explains at least some of the loss of heather moorland experienced in the middle of the 20th century.

Where mosaics of habitats occur, each with their own mix of palatable and unpalatable species, getting the right level of grazing to suit every component is difficult. Fencing may be helpful in some places, but needs to be carefully considered and planned to avoid problems. Where domestic livestock are involved, shepherding can certainly help, but this is not always easy or economic. Likewise, with wild herbivores such as deer, it is not simply a case of total numbers in a given area. Just as important is how the animals move around and use the area, both seasonally and daily, in response to weather, disturbance etc. There is still much we have to learn.