TIMBER TREATMENT AND WOOD SCIENCE
Cracking down on degrade by Dan Ridley-Ellis NapierUniversity
T
imber processors have always been concerned with timber defects that relate to issues in the tree, but accelerating changes in climate, silviculture and the drive for increased growth rate, give cause for concern that certain problems may be coming more common. These kinds of defects manifest as cracks, malformed wood, discolouration and increased susceptibility to rot. They cause increased reject, and in the worse cases can interrupt the sawing process. Sometimes these defects can be seen on the logs or standing trees, but often it is not apparent at the time of harvesting, and only becomes visible when cutting. Despite the headaches this causes, there is currently little documented
information on the nature of these degrade issues, prevalence, causes and impact on timber. It is not even known whether there is more than one underlying cause. There are three aspects to the research problem: • What are these degrade issues? • And what causes them? • Where do these degrade issues occur? • What is the impact? And how can it be mitigated? This kind of research is best be done as a collaboration between researchers, growers, harvesters and processors. The Strategic Integrated Research in Timber (SIRT) network has started work on this and if you are willing to help with this study you can use an online form to report instances of cracks, shakes, splits, and similar defects, as and when you encounter them.
The study is interested in defects that occurred before the timber is dried, and that were present in the living tree (even if not visible on the standing tree or log at the time of harvest). Your descriptions and location reporting will be used to research this issue, better understand the causes, and reduce its effects in future. This survey is the first stage of research, to help plan more specific work looking at the frequency
Above: two downgrade close ups (picture Dan Ridley-Ellis) Above right: Tiling batten end grain (picture Napier University Allan Shedlock)
Rate of growth and density – a ring of truth?
beX student Greg Campbell Andrews
48 FORESTRY & TIMBER NEWS • December 2019
It is widely thought that growth ring width is a good indicator of wood density – that wider growth rings mean the wood is of low density. In many species there is, in fact, no correlation between ring width and wood density. In some, it is even the other way around. But for spruce, we do expect wider rings to mean lower density. Indeed, we have known for more than half a decade that for UK-grown Sitka spruce the latewood width is relatively constant, meaning wider rings are proportionally more of the lower density earlywood. But, this is not quite the whole picture when it comes to grading for density using ring width. When grading we are not concerned with average density, but rather the lowest density we can expect (quantified by the characteristic, lower 5th percentile, in modern standards).
CONFOR.ORG.UK
