Bark-stripping on Norway spruce by red deer in Sweden: level of damage and relation to tree characteristics

Abstract

Red deer are increasing and spreading in Scandinavia. The species is capable of causing severe damage to Norway spruce through bark-stripping. We studied occurrence of bark-stripping on 18,000 trees in six study areas within two different regions in Sweden. The susceptibility for damage was related to morphological characters of the trees (bark thickness, branchiness, stem diameter) and whether the trees had old damage or not. In southernmost Sweden, 83, 89 and 92% of the stems were damaged in the three study areas, whereas 2, 8 and 46% was damaged in the three study areas in the region further north. Gnawing was the most common type of damage. Peeling was rare in the northern region but more frequent in the southern region. Bark-stripped trees had on average fewer branches, thinner bark and smaller diameter compared to undamaged trees. Furthermore, the risk of fresh damage was higher for already damaged trees in the northern region whereas the opposite pattern was evident in the southern region. Silvicultural measures may indirectly affect the risk of damage since it may affect branchiness, diameter and number of damaged trees left after thinning.

Keywords:

• Bark
• Cervus elaphus
• forest management
• Picea abies
• tree morphology
• wildlife management

Acknowledgements

The study was financed by The Swedish Environmental Protection Agency and The Royal Swedish Academy of Agriculture and Forestry through Stiftelsen Carl-Fredrik von Horns fond. We thank the owners, the forestry management and the wildlife management of the estates in the study: Holmen Skog, Virå Bruk, Fjällskär, Christineholm, Tista, Christinehof, Kronovall, Krageholm, Bellinga, Rydsgård, Ågerup-Elsagården, Hjularöd samt Övedskloster. We also thank Region Skåne/Stiftelsen Skånska Landskap, Valinge gård/Ittur Jakt and Virå Bruk for accommodation during the fieldwork. Lars Andersson, Skogsstyrelsen Skåne helped with field instruments and Henry Karlsson, Skogsstyrelsen Sörmland gave guidance and advice. We are grateful to Sophie Gröndahl, Anders Kastensson, Johan Nilsson and Josefina Zidar for their efforts during fieldwork! Roger Bergström and Henrik Andrén offered good advices in planning and analysing the study.