Effects of scarification on seedbed coverage and natural regeneration after a group seed-tree cutting in a black spruce ( Picea mariana) stand

Abstract

A study comparing two scarification intensities (single and double passes) was established 3 years after harvesting a black spruce-mosses stand using the group seed-tree method. The effects on black spruce ( Picea mariana) (Mill.) B.S.P.) advance growth, natural seedling establishment and competing vegetation were examined in relation to seedbed changes over a 5-year period. Scarification was effective in controlling ericaceous shrubs and it greatly changed seedbed types. It removed 50–70% of the feather moss coverage, the effect being related to intensity of treatment. The F horizon was the dominant seedbed produced by scarification which also exposed underlying layers more favorable for seed germination. After 5 years, the two scarification intensities improved black spruce stocking from natural seeding (40–47%) compared with elearcut only (32%). Stocking decreased linearly with distance from seed-tree groups which appeared to be efficient up to 50 m only. Scarification greatly increased paper birch ( Betula papyrifera (March.)) regeneration proportionally to intensity; the number of seedlings was doubled by the single pass (6333 ha −1) and more than tripled by the double pass (11 625 ha −1) compared with the control (3417 ha −1). The treatment also removed between 50 and 60% of the black spruce advance growth of layer origin, which resulted in a 20% decrease in stocking (absolute value). However, when layers and seedlings of black spruce were taken together the stocking reached 60% in both scarification intensities. In terms of total number of stems, scarification caused a 40% decrease in density coupled with a strong reduction of the layer:seedling ratio (2.7 to 1.6). The general trend shows a significant increase in the growth of layers 6 years after logging. Growth patterns of individual stems suggest that layers with a good growing potential started their height growth increase 3–4 years after logging.