How does grazing affect biodiversity?

It is not grazing alone that affects biodiversity, but rather the management of grazing that can affect biodiversity.

Poor management–which means turning out livestock to a large area and not moving them for several weeks or months–can decrease biodiversity, causing more desirable species to be pushed out by the less desirable species, and more species that are more suited to heavy grazing (which there are few [much more are forbs or weedy species, not grasses], unlike those that are less suited to heavy grazing) to come in. Poor management invites livestock to selectively graze whatever plants they want and how often they graze a particular spot, which in turn invites overgrazing as well as undergrazing.

Good management–which involves actively managing how long livestock are grazing a particular paddock and how long the plants get rest, what time of year they graze that area, and how many animals are actively grazing at a single point in time–will do the exact opposite, in fact increase biodiversity. When cattle can graze plants that have set seed, especially if these are desirable species, they can move these seeds from one location to another with their manure. Undesirable species would still be present, but they become less of a nuisance and much less noticeable than if livestock were poorly managed.

When a whole herd of cattle or sheep can be moved around on a large piece of land every one or three days, allowing at least 30 or 40 days of rest to each paddock on that piece of land, the soil and the plants on it improves. When livestock are no longer allowed to damage riparian and wetland areas and watered in a location that takes livestock away from these sensitive areas, the biodiversity also improves and increases. But, these areas should still be grazed, just not as often as the upland, non-wetland areas.