Woodland can be grazed year-round or seasonally. If your woodland has been divided into more than one grazing management unit, you can vary the seasonality or duration of grazing between units.
Year-round grazing avoids the need to move the stock on and off the site at set times but, like winter grazing, implies winter feeding or supplementary feeding. Year–round grazing can be appropriate if stocking densities are low. On small sites (<50–100ha), however, it may well be difficult to achieve year–round stock grazing at low densities. Seasonal grazing may therefore be useful at such sites but the likely effects of grazing at different times of the year will need to be considered.
The effect of seasonal grazing on the habitat will vary depending on the season selected. Seasonal grazing permits fine-tuning of the grazing regime to maximise benefits to the habitat or to key species. If a seasonal grazing regime is planned, autumn is often the most appropriate grazing season, for the following reasons:
Spring is the least appropriate time of year to graze a site heavily for flowering field–layer plants in general and in particular for spring–flowering, butterfly nectar–source plants. Heavy spring and summer grazing will reduce overall plant species diversity and encourage dominance of the most resistant or robust species in all plant communities. Light grazing, however, may be appropriate on certain sites.
Summer (May – Oct)
Heavy grazing in the summer imposes the greatest potential for severe, or irrecoverable damage to tree seedlings and saplings. Grazing domestic stock remove biomass from the system and, especially in spring and summer, deplete resources of a wide range of nectar, pollen and other invertebrate food sources, reduce structural diversity and consequently the number of many habitat types and niches for a range of organisms.
Biomass will naturally be at its annual maximum by autumn (if the area has not been heavily grazed during the summer). In general the autumn offers most, if not all, of the potential benefits of maintaining a controlled large herbivore presence in semi–natural woodlands to occur, while minimising potential disadvantages associated with grazing in such woodlands. Precise timing will depend on the objectives and the desired outcomes.
Winter-only grazing may create sufficient ground disturbance to enhance the chances of tree seeds finding favourable niches for germination over the following seasons. It may offer benefits in reducing bracken and other leaf litter and it is likely to have little negative impact on spring-flowering and annual field layer species.
However, grassy forage becomes less available and less attractive in winter, so grazing by over-wintering animals may result in severe browsing damage to heath species, shrubs and young, regenerating trees.
In winter, soils are at their most vulnerable to poaching damage. This is likely to be most severe around supplementary feeding sites.