The wood properties and sawn-board quality of South African-grown Pinus maximinoi (HE Moore)

Abstract

This report summarises results of past research in South Africa on the wood properties and qualities of P. maximinoi, supplemented by results of a study performed recently on an approximately 15.5-year-old provenance trial at Wilgeboom after it had been severely damaged by fire. The trees selected to study wood density, branching characteristics and sawn-board quality of the species, were previously selected for further breeding for their superior volume growth and stem form. Differences in mean internodal length and mean branch diameter were statistically highly significant among provenances, on average being longer and generally thicker than those of the P. elliottii and P. patula. The bark-layer of P. maximinoi was thicker than that of P. patula but it differed little in thickness with that of P. elliottii. Provenance means in air-dry wood density varied within a relatively narrow band of 0.457 to 0.483 g/cm3, with an average mature wood density resembling closely that of P. patula. However, P. maximimoi was characterised by increased uniformity in density across its radius, as it tended to form denser wood in the central parts of its stem, causing its pith-to-bark density gradient to be flatter. Growth rate had no effect on wood density, but improved radial density uniformity was clearly associated with increased growth rate. Sawn boards were of good quality and showed little warp after drying despite the fact that some of the trees were slightly crooked, with possibly a higher incidence of compression wood. Compared to P. patula and P. elliottii this species exhibited a darker brown colour with almost a reddish tinge when freshly cut. The annual rings were hardly recognisable on rough-sawn surfaces. Wandering pith often occurred in some boards as a result of the higher degree of stem crookedness. Since the branches of P. maximinoi tend to be arranged in whorls, it can be expected that the impact of knots on the strength of the sawn boards would predominantly be the result of the combined effect of knots grouped together, rather than individual knots. This is also a valuable attribute, as the species lends itself to the production of relatively long knot-free board sections from the unpruned parts of the stem, which would enable manufacturers of finger-jointed products to increase the volumes and diversity of their products, especially where appearance is important. Loose knots occurred more frequently in boards cut from P. maximinoi compared to the two controls, most likely as a result of pruning that was carried out too late considering the fast growth of the species.

Keywords: Pinus maximinoi, provenances, wood density, knots, CAMCORE, sawn-board quality

Southern African Forestry Journal Vol. 208, 2006: 39-47