Mortality of balsam fir and black spruce advance growth 3 years after clear-cutting

Abstract

The effects of balsam fir (Abiesbalsamea (L.) Mill.) and black spruce (Piceamariana (Mill.) B.S.P.) seedling attributes on survival were measured on four cutovers regenerated to black spruce and three regenerated to balsam fir. In each of these, about 240 stems were permanently identified shortly after logging and their main characteristics were noted. Survival was assessed after 1 and 3 years. First-year mortality reached 24% for balsam fir and and 21% for black spruce. It varied with height and seedling quality. Mortality during the second and third year after harvesting was less important and was more evenly distributed between the different height classes. When all height classes were combined, the logistic regression calculated for total balsam fir mortality was able to correctly classify the observations in 74% of the cases by using three variables: prerelease height growth, lean angle, and a wound index. For black spruce, seven variables were needed to correctly classify 78% of the observations. These were: height, prerelease height growth, live crown ratio, lean angle, distance to the straightening point, and two wound indices. Separate logistic regressions were calculated for stems smaller or taller than 30 cm. These regressions performed considerably better for the taller height class for both species. For balsam fir, lean angle and one or another wound index still remained in relation with survival. For black spruce, prerelease height growth and lean angle remained in relation with survival. Distance to the straightening point was only retained for stems below 30 cm while live crown ratio and the two wound indices were retained for stems over 30 cm. These results suggest that an evaluation of seedling quality using measures of previous suppression and logging damage should be introduced in regeneration surveys to better predict the evolution of a cutover after harvesting.