A comparison of long-term effects of scarification methods on the establishment of Norway spruce

Scarification is the most common measure to improve the planting environment in Sweden. However, different scarification methods give varying results. During the early 1990s, a nation-wide experiment with 10 field installations was established in order to test the effect of several scarification methods, including two intensities of soil inversion and mounding, on growth of planted Norway spruce seedlings and in comparison with no scarification (i.e. control). Eighteen growing seasons after planting, a higher seedling survival was found following soil inversion (77 per cent for normal and 76 per cent for intensive) compared with mounding (67 per cent) and control (57 per cent). The mean height of the planted trees across all sites 18 years after planting was 413 and 430 cm following normal and intensive soil inversion, respectively, 424 cm after mounding and 346 cm in the control. The difference in height between the scarification treatments and the control corresponded to a time gain of 4 years of growth after 18 years. However, the length of the leading shoot was not affected by scarification after 14–18 years, indicating that scarification did not affect growth beyond the establishment phase. Scarification reduced variation in height of the planted trees. On scarified plots, the number of naturally regenerated trees increased with more than 100 per cent to reach a mean value of 2300 stems per hectare.