Evaluation of morphological attributes as response variables to perennial competition for 4-year-old black spruce and jack pine seedlings

Abstract

The sensitivity of seedling morphological attributes to changing competition levels was evaluated on 4-year-old black spruce (Piceamariana (Mill.) B.S.P.) and jack pine (Pinusbanksiana Lamb.) seedlings to determine the most appropriate response variables to be used in the assessment of early plantation performance. A total of 720 seedlings (360 per species) were sampled between 1987 and 1989, covering a range of stock types, soil textures, and competition levels. A competition index, derived from hemispherical photographs, provided an estimate of incident radiation received by each sampled seedling. Seedling stem volume at time of planting was used as a covariate in the regression analyses. Stratification by plantation was done to account for variations in site quality. The results from this study demonstrated that total height or current height increment were not reliable for quantifying individual seedling response to inter specific competition for 4-year-old black spruce or jack pine plantations. Overall, the most consistent response variable was total seedling dry weight. Coefficients of determination ranged from 0.116 to 0.534 for black spruce and from 0.601 to 0.810 for jack pine across the range of sites and stock types. If it is inappropriate to determine total seedling dry weight, root collar diameter would be the best substitute. Correlation coefficients between these two variables were 0.897 for black spruce and 0.912 for jack pine.