Influencing factors on red deer bark stripping on spruce : plant diversity, crop intake and temperature

Sammanfattning: Red deer (Cervus elaphus) is increasing in distribution and population density in several regions of Europe and may cause severe damage in commercial forestry and agriculture. Bark stripping is the main problem in forests, especially on Norway spruce (Picea abies). It has been suggested that an imbalance in the nutrient intake, and especially a diet composed of high amounts of easily-digestible macronutrients, such as crops, can lead to an increased urge to consume bark. Feeding on brassicas, for example oil seed rape (Brassica napus) might have this effect. My aim with this study is to investigate the relationship between intake of oil seed rape and bark stripping on Norway spruce by red deer during early spring. I did this by a controlled feeding experiment with four groups of captive red deer in southern Sweden. All groups were given spruce logs every week, while only two groups had access to fresh harvested oil seed rape plants. In addition, influence of air temperature and plant diversity was taken into account, and the deers’ selectivity of different parts of oil seed rape plants was measured. My results show that red deer bark stripping can be considerable not only during periods of food shortage but also during spring green-up. There was no significant influence of oil seed rape on bark stripping. This was most likely due to overshadowing factors: air temperature was significantly positively related to bark intake, and red deer in enclosures with lowest plant diversity consumed the highest amount of bark. Finally, red deer showed a positive selection towards leaves, rather than stems, of oil seed rape, and this selection increased with the amount of oil seed rape provided (the dose). I conclude that to understand and to mitigate bark stripping by red deer on spruce several interactive effects must be considered, such as crop intake, plant diversity in the habitat and air temperature. Obviously, interactions between agriculture and forestry needs to be further studied, and more knowledge is needed before we can implement suggestions in wildlife management and forestry.