The effects of initial spacing on growth and crown development for planted northern conifers: 37-year results

Abstract

A spacing trial was established near Thunder Bay, Ontario in 1950. This trial consisted of black spruce (Picea mariana (Mill.) B.S.P.), white spruce (Picea glauca (Moench) Voss.), and red pine (Pinus resinosa Ait.) each established at three different spacings: 1.8 m, 2.7 m, and 3.6 m. This study examines the differences in growth and crown development as attributed to initial spacing, after 37 years. In addition, a benefit/cost analysis was performed to evaluate the economic efficiency of the various species/spacing combinations. Diameter at breast height, live crown length, and crown width, all exhibited significant (P < 0.001) increases as initial spacing increased, irrespective of species, but, height demonstrated a decreasing trend (P < 0.020). Gross total and merchantable stem volume per tree increased for all species as initial spacing increased; however, volume production per unit area decreased significantly for all species as spacing increased. The shift to higher-valued products from the wider-spaced plantations appeared to provide the best economic return. As a result of both greater merchantable volumes and greater percentages of these volumes available as a higher-valued product, benefit/cost ratios for red pine (0.995 to 1.337) were greater than those for the spruces (0.595 to 0.866). Although red pine currently represents less than 4% of Ontario's total regeneration effort, the results from this study suggest it deserves further consideration on some boreal sites. Key words: spacing trial, plantation growth, crown development, black spruce, white spruce, red pine, benefit/cost ratio