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

Abstract

Summary The relationship between bordered pit aspiration, pit sizes and permeability measured as preservative uptake and expressed as porosity was examined in two species of spruce, Sitka spruce ( Picea sitchensis (Bong.) Carr.) grown in the UK and Eastern spruce ( 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 solution was allowed to fl ow in either the longitudinal or tangential direction of the stem wood and the uptake was assessed. Bordered pit anatomy was examined by light and scanning electron microscopy and image analysis was used to characterize the samples. The permeability of the wood declined following drying but less so in the Sitka spruce. From an analysis of measurements made on the wood features it appeared that basic density, latewood percentage and degree of pit aspiration were the most important features explaining these results. The structure of the bordered pits varied between the two species and the relative size of the aperture in comparison with the pit chambers was greater in the Eastern spruce. The effects of these and other variables including differences in conventional drying systems and natural tree responses to environmental conditions on pit behaviour affecting permeability are discussed.