Abstract
The effectiveness of manual release to favor growth and survival of black spruce seedlings was determined in eastern Quebec plantations. Up to three releases over as many consecutive years, and two weed cutting methods, were tested for two types of competing vegetation composed of either raspberry and fireweed (Squatec site) or shade intolerant deciduous trees (Lake Anna site). Five weed cutting periods, from June through October, were also tested at this last site. Seedling growth and survival were not affected by the number of releases. At the Squatec site, seedlings released with a brush cutter were 24% larger in diameter at the collar, and on average 12% higher, than untreated seedlings after 10 years. Weed cutting during the growth season (June through September) enhanced seedling growth. At the Lake Anna site, the best growth enhancement was produced by cutting out all competing vegetation. Seedlings in these plots were 53% larger in diameter at the collar and on average 79% higher than control seedlings. Effects of the realease treatments on height and diameter growth increased with time relative to untreated seedlings, showing that treatments had a long-lasting effect. Furthermore, a variance analysis of skewness and kurtosis coefficients was used to determine the effect of competition on the structure of seedling dimensions. After 10 years at the Squatec site, diameter and height distributions were skewed to the left and to the right, respectively. After the same lapse of time at Lake Anna, height and diameter distributions in released plots were skewed to the right opposite to the left in untreated plots. At both experimental sites, seedling dimensions were arranged in a hierarchical manner nearly always similar between released and control plots as a result of competition effects that were lasting since the time of release. Results suggest that release effects should be examined not only on the average growth of seedlings but also on stand structure.
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