9: Herbivore impact

What information does the survey provide and why does it matter?

The survey recorded overall herbivore impact for each area of native/ancient woodland. Herbivore impact scores are in four categories. Values calculated are from: A-low (herbivoreimpact), B-medium, C-high to D-very high in the period leading up to the date of the field work. Cause of the more severe impacts, can include trampling and/or poaching damage, canopy fragmentation, heavy browsing, barkstripping and a heavily grazed sward.

Herbivores, especially deer, are an integral part of woodland ecosystems. They are important in influencing woodland regeneration, composition and structure and therefore in shaping woodland wildlife communities.

Some periods with no grazing at all can be neutral or beneficial for woodland condition, but a long-term absence of herbivores can lead to negative effects, for example when dense thickets of young trees develop and shade out ground flora and lower plant species.

However, heavy browsing by deer or sheep prevents woodland regeneration, and this is currently the most frequent and widespread threat to the condition of designated woodland features.

In general light grazing and browsing is desirable to promote both a diverse structure and seedling establishment.

Low herbivore impact (i.e. values of A or B) is one of the four attributes in the Native Woodland Condition indicator. This is valuable as a general regional or national indication of whether herbivore impact is suitable, but each site needs to be considered on its merits and is different and site-specific objectives needs to be set.

For example, there are upland oakwoods where a moderate level of grazing and browsing is desirable to maintain conditions for woodland bryophytes or lichens. In some native woods managed as wood pasture where moderate or high grazing levels are desirable for most of the time.

Policy relevance

The Scottish Forestry Strategy includes a priority action to encourage good management of deer to secure biodiversity objectives and effective woodland management.

How can the NWSS data be used?

Type of useNationalRegional/local authorityLandscape/site scale
Factor into woodland management plans n/a n/a Yes
Assessing herbivore impact at regional or landscape scale to prioritise effort (e.g. advisory and financial) n/a Yes Yes
Include as a core attribute in assessment and reporting on condition of native woodlands Yes Yes n/a