Comparison of the bordered pits of two species of spruce (Pinaceae) in a green and kiln-dried condition and their effects on fluid flow in the stem wood in relation to wood preservation

The relationship between bordered pit aspiration, pit sizesand permeability measured as preservative uptake and expressedas porosity was examined in two species of spruce, Sitka spruce(Picea sitchensis (Bong.) Carr.) grown in the UK and Easternspruce (Picea orientalis (L.) Link.) grown in Turkey, before(in the freshly felled green condition) and after kiln drying.A 2.5 per cent chromated copper arsenate preservative solutionwas allowed to flow in either the longitudinal or tangentialdirection of the stem wood and the uptake was assessed. Borderedpit anatomy was examined by light and scanning electron microscopyand image analysis was used to characterize the samples. Thepermeability of the wood declined following drying but lessso in the Sitka spruce. From an analysis of measurements madeon the wood features it appeared that basic density, latewoodpercentage and degree of pit aspiration were the most importantfeatures explaining these results. The structure of the borderedpits varied between the two species and the relative size ofthe aperture in comparison with the pit chambers was greaterin the Eastern spruce. The effects of these and other variablesincluding differences in conventional drying systems and naturaltree responses to environmental conditions on pit behaviouraffecting permeability are discussed.