Current issue: 54(2)
The effects of precommercial thinning on the quantity and external quality of young Scots pine (Pinus sylvestris L.) stands were examined over two 10-year periods in an experiment comprising five stands growing on sub-dry sites in Finnish Lapland, northern Finland. The thinning treatments applied resulted in stand densities of 625, 1111, 1600, 2500 and 4444 stems ha-1 and a no-treatment, unthinned plot with a randomised block lay-out of two or three replications in each stand. The dominant height of the stands varied between 4 and 8 m at the time of thinning.
The trees reacted only slightly to the increase in growing space during the first ten years following precommercial thinning. During the second 10-year period, increased growing space was reflected more clearly in diameter and volume increment. These reactions were more evident in stands thinned at an early stage. The increment of the thinnest 100–200 trees ha-1 in each treatment was poor. The results showed that when the main principle in precommercial thinning is to achieve even spacing, the remaining smallest trees fail to react positively to the increase in growing space. In other words, the target of precommercial thinning should be to concentrate the increment on the tallest trees, even though they are located in groups. The external quality of the trees in stands where precommercial thinning was carried out at a later stage was high, and the diameter of the thickest branch along the butt log remained under 20 mm. Branch diameter was greater in stands thinned at an early stage. The effect of precommercial thinning on branch diameter when comparing the extreme treatments averaged 5 mm. When the aim of stand management is to combine high quality and good yield in naturally regenerated Scots pine stands in northern Finland, precommercial thinning should not be carried out before the dominant height of 7–8 m. The intensity of precommercial thinning depends on the yield targets of the first commercial thinning. A spacing of 2,500 stems ha-1 satisfies the requirements of both high quality and adequate yield.
The shape of Scots pine (Pinus sylvestris L.) knots close to the pith of butt logs was investigated. 1,100 knots were split in a vertical direction, and their shape was measured. Knot diameter and branch angle were calculated at a distance of 40 mm from the pith of the stem. The mean diameter of all the knots in the material was 14 mm, and the branch angle 70°. Regression analysis was used to devise a formula for predicting branch angle on the basis of knot diameter. Knot size and branch angle were negatively correlated. Especially the shape of larger knots was curved. Knots achieved their maximum diameter at distance of 4–5 cm from the stem pith. The branch wood was almost completely situated above the formation point of the branch.
The PDF includes an abstract in Finnish.
The study based on young Scots pine (Pinus sylvestris L.) of varying density showed that number of living branches per whorl and total number of living branches per tree were negatively correlated with stand density. On the contrary, the number of dead branches increased with increasing stand density. The diameter of living and dead branches decreased with increasing stand density. Consequently, the branchiness, i.e. the share of the branch cross-sectional area from the surface area of the stem, decreased in dense stands compared with the thin stands. At the densest stands the branchiness, however, levelled of indicating a greater decrease of the radial growth at stems than at branches. The 2/3 power law described relatively well the relationship between stand density and mean squared branch diameter of living branches.
The PDF includes a summary in English.
The material comprised 12 Norway spruces (Picea abies (L.) H. Karst.) from Central Finland, with 2,118 branches. The exact location of the branches on the stems, their diameter at the thick end, their length, and the green weight of all the branches was measured on two-metre lengths of the stem.
According to the results, the diameter of a branch can be estimated very accurately from its length. The variation of branch diameter along the stem was also very regular, although there were considerable differences from one tree to another. The greatest work requirement for trimming was in the middle and upper parts of the green crown. Branch variables per tree, such as the number and cross-section area o the branches, could be satisfactorily estimated from the volume or breast-height diameter of the stem.
The PDF includes a summary in English.