Field preformance of outplanted Norway spruce: effects of organic matter amendments and site preparation

Norway spruce (Picea abies (L.) Karst.) seedling survival and growth response to site preparation methods involving different utilization of humus (forest floor material from the F- and H-layers) and chipped slash were studied on a recently clear-felled spruce site in northern Sweden. Five mounding treatments (pure mineral soil, mineral mound covered by or mixed with either of the two types of organic matter) and two unscarified treatments (with or without a chipped slash mulch) were applied in a randomized block design. Half of the blocks were planted in the year of clear-felling (1990) and the remaining blocks in 1991. Containerized (1/0) seedlings mechanically protected against Hylobius abietis L. were used. For both planting occasions, seedling survival after 3 years exceeded 90% in most treatments and the occurrence of injuries was significantly (p < 0.05) affected by soil treatments only in the 1990 plantation. In general, the largest seedlings (heights dry weight, needle weight, needle lengths leading shoot terminal bud diameter) developed in mounds containing humus, and mounds containing chipped slash produced the smallest seedlings. Mixing chipped slash with mineral soil appeared to suppress seedling growth. The results also indicate that planting delay should be avoided to permit Norway spruce seedlings to benefit fully from the growth-stimulating potential of humus. Successful planting without site preparation might depend on the avoidance of planting delay.