The effect of water storage on the cell-structure of Sitka spruce (Picea sitchensis) with reference to its permeability and preservation
IRG/WP III 3A
J A Dunleavy, A J McQuire
Commercial treatment trials with full sized transmission poles have shown that water storage considerably improves the permeability of Sitka and Norway spruce. These results were confirmed by laboratory measurements which showed that in the sapwood of ponded Sitka spruce there is a vast improvement in permeability in all three grain directions. Heartwood permeability does not seem to be affected to any great degree. Detailed examination of the ponded sapwood by optical and electron microscopy showed that the tori and bordered pit membranes have been destroyed. This would explain its increased longitudinal and tangential permeability. Destruction of the bordered pit membranes would also affect radial permeability but it is thought that the main factor contributing to increased radial penetration was the partial breakdown of the crossfield pit membranes of the ray parenchyma cells. The microscopic examination showed no evidence of cell wall degradation. Preliminary tests have not revealed any deterioration of the strength properties of the wood due to prolonged ponding. There is evidence to indicate that the destruction of the pit membranes was caused by bacterial attack. Microbiological investigations are now in progress and it is hoped that this work will establish the identity and the mechanism of attack of these organisms.