The forage utilisation rate is a measure of the amount of plant material removed from an area by herbivores over a fixed time period.

This can be expressed as a percentage of the total dry matter production for that area. Thus a 20% utilisation rate means that 20% of the plant material is removed.

Target utilisation rates will vary according to the biodiversity objectives of the woodland. If you are looking for natural regeneration, for example, your target utilisation rate will be low.

Utilisation rates can be seen as a way of measuring herbivore impact. Target rates for woodland grazing will normally be lower than those sought for an agricultural field. Thus for woodland grazing:

• 10-15% target utilisation is likely to result in low herbivore impacts.
• 20% target utilisation is likely to result in medium herbivore impacts.
• 30% target utilisation is likely to result in high herbivore impacts.
• 40% target utilisation is likely to result in very high herbivore impacts.

If your woodland or management unit contains areas of open ground with neutral or semi-improved grassland, these areas could be grazed at much higher intensities without causing any adverse effects to the biodiversity of the grassland habitat. Up to 70% utilisation is quite normal for these habitats.

Because grassland will act as a magnet to grazing animals it is possible to have an anticipated 70% utilisation rate for these habitats and still expect a 10-15% utilisation rate within the woodland habitats, assuming the woodland is of a type that offers poor grazing potential. As the productivity of the grassland habitats is high, the high target utilisation rate combined with high productivity is likely to result in a significant increase to the annual target for dry matter removal in the woodland or management unit as a whole. 

It is possible to anticipate relative utilisation rate for various habitats at a given stocking density. The table below suggests relative utilisation rates that would follow from a stocking density expected to result in a low (10-15%) rate in the woodland habitats.