Effects of stump harvesting on soil C and N stocks and vegetation 8–13 years after clear-cutting

Abstract

Effects of stump harvesting on coarse woody debris (CWD), soil and vegetation were investigated 8–13years after clear-cutting of eight forest stands located at two sites, Honkola and Haukilahti, in Central Finland. Norway spruce (Picea abies) was the dominant tree species in the harvested stands. Four of the stands were subjected to mounding and four were stump-harvested. Logging residues were removed at harvest from all eight stands.The amount of CWD remaining after stump harvesting was estimated from basal area of remaining stumps, diameter and length of logs and by weighing smaller pieces of dead wood. Moss and field layer vegetation cover was estimated by a point-intercept method and the diameter of young trees was measured to estimate basal area. Soil carbon and nitrogen stocks and pH were determined in the humus layer and down to 25cm depth in the mineral soil. The degree of soil disturbance was visually assessed in the field.Basal area measurements on remaining stumps suggested that about 75% of the stumps had been removed from the stump-harvested stands, which is a typical stump harvesting rate in Finland. The amount of remaining stumps and root biomass was significantly lower in stump-harvested stands than in stands where stumps had been retained, whereas differences between mounding and stump harvesting were not significant for the other types of CWD. Stump harvesting had no significant effect on the cover of field layer species, total moss cover or vegetation composition. Total stem density was almost twice as high in stump-harvested stands as in stands where stumps were not harvested, due to significantly higher stem density of Betula pendula Roth., whereas no effect was observed on the basal area of the other tree species. No significant treatment effect on soil carbon and nitrogen stocks or on degree of soil disturbance was detected, but the higher density of Betula indicates higher exposure of mineral soil during the years following stump removal. In conclusion, stump harvesting seems to promote natural establishment of Betula seedlings, but does not change tree productivity.