The proximity of rapeseed fields influences levels of forest damage by red deer.
Abstract
Deer can show transitional use between agricultural fields and forests for foraging and shelter. Such transitional use may affect forest damage as nutrient balancing theory suggests that if deer ingest large amounts of nutrient-rich food, complementary browse, such as bark, may be required to balance the diet. We investigated the relationship between the level of red deer Cervus elaphus bark-stripping damage in 68 Norway spruce Picea abies stands and the presence of rapeseed Brassica napus fields - an energy-rich crop preferred by red deer - in the surroundings, hypothesizing that damage increases with decreasing distance to rapeseed fields. We also considered other potentially influencing factors, such as supplemental feeding, alternative forage availability, and deer use of spruce stands as indexed by a pellet group count. Spruce stands closer to rapeseed had a significantly higher proportion of damaged stems. The increased level of bark-stripping damage was not explained by a higher stand use of deer closer to rapeseed fields, indicating that deer increase their consumption of bark in order to balance their diet. Similarly, spruce stands closer to supplemental feeding stations had significantly higher damage levels. In line with earlier findings, damage levels were negatively related to the amount of available browse in the forest. This emphasizes the importance of alternative forage for reducing the damage risk in forest plantations. Our study shows that the availability of fields with nutrient-rich food, such as rapeseed, as well as supplemental feeding needs to be considered when predicting the level of forest damage. With a high availability of nutrient-rich food in the vicinity of forest stands, a higher damage level can be expected and counteractions could be taken such as increased disturbance, harvest or changed choice of both crop and supplemental feed types. These actions may also be combined with a push-pull strategy where the deer are steered to disturbance-free zones insensitive to damage and with alternative forage. The importance of alternative forage availability on damage levels highlights the necessity for managers to actively promote tree and shrub forage within and around their production stands Our study shows that the availability of fields with nutrient-rich food, such as rapeseed, as well as supplemental feeding needs to be considered when predicting the level of forest damage. With a high availability of nutrient-rich food in the vicinity of forest stands, a higher damage level can be expected and counteractions could be taken such as increased disturbance, harvest or changed choice of both crop and supplemental feed types. These actions may also be combined with a push-pull strategy where the deer are steered to disturbance-free zones insensitive to damage and with alternative forage. The importance of alternative forage availability on damage levels highlights the necessity for managers to actively promote tree and shrub forage within and around their production stands.