Formation and prediction of resin pockets in Picea abies (L.) Karst.
1997
Temnerud, E. (SLU, Uppsala (Sweden). Inst. foer Virkeslaera)
This thesis deals with selection procedures of sawlogs and sawn timber to minimise the size and the quantity of resin pockets in wood from Picea abies (L.) Karst. The thesis is based on examination of sawn timber from 40 trees in one stand and 1260 sawlogs from five geographic regions in Sweden. The variation in resin pockets within trees and between trees is described. Efficient sampling procedures for the detection and quantification was tested by means of stereological methods using measures obtained manually or by CT-scanning. An additional experiment with Pinus sylvestris L. was performed to test if resin pockets could be induced by mechanical bending stress during growth. The size of resin pockets varied from a minimum length, width and thickness of 3.0, 2.5, and 0.5 mm to a maximum of 175, 65, and 7 mm, respectively. Light microscopy studies showed that resin pockets resemble wounds in the xylem and that they were formed mainly in the earlywood. Unbiased estimates of the quantity of resin pockets for wood lots can be based on large number of systematically sampled log ends (stem discs) or pith-fleck-sides of centre boards, using measures obtained manually or by CT-scanning. The average sum of lengths of resin pockets per volume unit wood was estimated to be 9.8+- 0.72 m/m3. The occurrence of resin pockets was 5.4 m/m3 in butt logs and 13.2 m/m3 in upper logs. Several stress factors may induce resin pockets which render the proposition of practical selection procedures of sawlogs more difficult. The recommendations based on this thesis are: for a minimised size and quantity of resin pockets sawn timber should be selected from the innerwood part of butt logs; and that sawmills should carry out continuous measurements of resin pockets and establish databases to successively gain control over the large variation in occurrence of resin pockets in wood.
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