Abstract
The number of planted trees per hectare influences individual volume growth, which in turn can affect wood properties. The objective of this study was to assess the effect of six different plantation spacings of jack pine (Pinus banksiana Lamb.) 25 years following planting on tree growth, morphology, and wood properties. Stem analyses were performed to calculate annual and cumulative diameter, height, and volume growth. For morphological and wood property measurements several parameters were analyzed: diameter of the largest branch, live crown ratio, wood density, and the moduli of elasticity and rupture on small clear samples. The highest volume growth for individual trees was obtained in the 1111 trees/ha plantation, while the lowest was in the 4444 trees/ha plantation. Wood density and the moduli of elasticity and rupture did not change significantly between the six plantation spacings, but the largest branch diameter was significantly higher in the 1111 trees/ha (3.26 cm mean diameter) compared with the 4444 trees/ha spacing (2.03 cm mean diameter). Based on this study, a wide range of spacing induced little negative effect on the measured wood properties, except for the size of knots. Increasing the initial spacing of jack pine plantations appears to be a good choice if producing large, fast-growing stems is the primary goal, but lumber mechanical and visual properties could be decreased due to the larger branch diameter.
Highlights
Tree spacing is an important silvicultural tool that influences the sequence of future silvicultural treatments required and, the stand attributes at harvesting age [1]
Tree mortality commonly occurs in plantations [3,5,6,7], but because our aim was to quantify the effect of tree spacing, only trees surrounded by all their initially planted neighbours were randomly considered in our selection
Plantation spacing had a significant effect on diameter at breast height (DBH) and stem volume for dominant stems (Table 2, Figure 1a,b)
Summary
Tree spacing is an important silvicultural tool that influences the sequence of future silvicultural treatments required and, the stand attributes at harvesting age [1]. Numerous studies have already shown that stand volume increases with narrower plantation spacing, up to a certain level [2,3,4]. An increased growth rate of individual trees may affect wood properties, and can influence the performance and value of end-use products [10]. Trees forming larger tree rings can result in a decrease in wood quality parameters like density [12,13]. This has been reported to be mainly the consequence of a difference in the earlywood/latewood proportion between slow and fast growing trees. Fast growing trees typically produce a higher percentage of earlywood, and in some cases lower density latewood, compared with slow growing trees (Zhang [14] (Picea mariana); Wang et al [15] (Picea mariana); Makinen et al [16]
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