The suitability of high pressure sap-displacement for the retention of UK grown spruce and pine
P D Evans, S D Hainey, A Bruce, G M Smith, B King
The concentration and radial distribution of copper, chrome, arsenic (CCA), and the moisture content and depth of radial checking in UK grown, field exposed spruce and pine poles treated by high pressure sap-displacement are examined. The concentration of CCA elements in samples obtained from increment cores is similar in Norway spruce, Scots pine and Corsican pine but is significantly lower in Sitka spruce. The concentration of chromium in all species, arsenic in Sitka spruce, Norway spruce and Corsican pine and copper in Sitka spruce are at a maximum in the outer sapwood and decrease centripetally with increasing core depth. In contrast, arsenic in Scots pine and Norway spruce at groundline and copper in Norway spruce, Scots pine and Corsican pine are at a maximum in the inner sapwood. The slopes of metal concentration against radial core depth are similar in Norway spruce and Scots pine but are significantly larger (steeper) and smaller (less steep) respectively in Sitka spruce and Corsican pine. Checking is more severe in Sitka spruce than in the other species and appears to be associated with steep moisture gradients. In Sitka spruce, checks penetrate the preservative treated annulus thus greatly facilitating decay since micro-organisms have access to untreated non durable wood. The results suggest that high pressure sap-displacement is suitable for the treatment and long term protection of Norway spruce, Scots pine, and Corsican pine but is inadequate for the protection of Sitka spruce. Modifications to the high pressure sap-displacement process that could improve the treatment of Sitka spruce are discussed.
Keywords: CCA; CHECKING; CONCENTRATION; HIGH PRESSURE; PICEA SITCHENSIS; PICEA ABIES; PINUS NIGRA MARITIMA; PINUS SYLVESTRIS; POLES; SAP-DISPLACEMENT; RETENTION