Browsing damage by roe deer on Norway spruce seedlings planted on clearcuts of different ages: 2. Effect of seedling vigour

Abstract

The effects of browsing damage by roe deer ( Capreolus capreolus L.) on Norway spruce ( Picea abies (L.) Karst) seedlings planted on clearcuts of different ages were studied in a field experiment. The experiment was established in 1993 on 0- to 4-year-old clearcuts in four sites, and seedling observations were made until May 1995. Half of the seedlings were planted in May and the other half was planted in October. Planting in two different seasons allowed the separation of the different effects of surroundings on the risk for a seedling to be browsed. Seedling vigour was estimated, using a needle colour index ranging from yellow to dark green. In addition, concentrations of nitrogen in needles and shoot axes were analysed. The needle colour index was well correlated with nitrogen concentration in both needles and shoot axes. The frequency of browsing was higher for seedlings with a dark green colour (high nitrogen concentration) than for seedlings with a light green or yellow colour (low nitrogen content). The average needle colour index was also correlated with the average frequency of browsing damage over different sites and years. Browsing damage tended to decrease with the height of surrounding vegetation, mainly owing to reduced seedling vigour, as long as the vegetation was shorter than the seedling. In cases where the vegetation was higher than the seedling, the physical protective afforded by the vegetation seemed to dominate. The needle colour index of seedlings tended to increase with height of slash which was most likely explained by a fertilising effect from decaying plant tissues. Browsing damage tended however to be reduced with increasing slash height. The increasing risk for a seedling to be browsed because of higher vigour, as a result of higher slash, seems to be balanced by the physical protection afforded by slash.