Skottbetning på granplantor i Kolmården : omfattning och påverkande faktorer

Sammanfattning: In the Kolmården area, northeast of Norrköping in south-central Sweden, it was discovered that shoots of spruce Picea abies, plants to a seemingly large extent had been browsed by deer. The area inhabits a dense red deer population, alongside with moose and roe deer, and red deer is thus suspected to cause the damage. The main purposes of this study are, however, to estimate the extent of the shoot-damage and to investigate what factors that may affect the browsing of shoots. For each stand information was recorded about the age of the plants, area for the stand, height over the sea for the stand, site productivity, type of plants and stand-history. The study was done in three areas: Simonstorp, Stavsjö and Valinge. At Simonstorp and Stavsjö, respectively, 10 stands were chosen for study and on Valinge six stands. In each stand, 10 plots were sampled. The sampled plots were characterised according to moisture, vegetation and the distribution of tree species. The height of the spruce plants on each sampled plot was record. The results showed that Simonstorp had 27 %, Stavsjö 30 % and Valinge 10 % shoot-damage. Simonstorp and Stavsjö are more homogeneous forestlandscapes, whereas Valinge has a mixed landscape with forest and fields. The results therefore seem to support the belief that deer-browsing on spruce-plants mainly occurs in forest-dominated and less productive areas. Plants in age between two to four and with a height of 35 to 95 cm were the most vulnerable to get damaged. There was a negative correlation between amount of broad-leaved plants and damage on spruceseedlings. It is thus possible that a preference for broad-leaved plants results in reduced browsing on the spruce-plants. This probably because the deers rather graze on the leaf rather than the spruceseedlings. Other factors like type of plant, area, share of vegetation, stand-history and site quality did not show any significant effect on the level of damage. However, it is worth to mention that the only stand that was planted on former arable land had the highest level of damage with 48 % of the plants damaged. This stand appeared in Simonstorp. The problem with the browsing on spruce-plants was not as extensive as the Holmen Skog first thought. But to get a more certain conclusion about that, more research should be done. For example a more detailed study of factors that may affect the extent of the damage. It is also an important question to find out what species that is causing the damage. If browsing on spruceseedlings is a common and widespread problem, and if red deer is the species causing it, it should be an important question for the Swedish forestry, especially as red deer is increasing and spreading in Sweden.