Edinburgh Napier University

  There are several different concepts of wood density, such as specific gravity, basic density, dry density, and oven dry density. These are often confusing, and sometimes poorly described in the literature, but they can be unambiguously defined and measured in simple and repeatable ways. This makes density a popular measurement in wood science and timber processing, but also leads to a general over-estimation of how well we can actually know the density of a particular wood resource, especially when it is reported with a spuriously high level of precision. For construction timber in Europe, the standard reference value for density is usually equivalent to mass at 12% moisture content, divided by volume at 12% moisture content. Even in this, apparently very straightforward, case there are some open questions about how we measure, and use density. The answers to these are unknown (and possibly unknowable), yet they could have practical, real-world, implications if we overreach the true level of knowledge of density. We should not forget that there is still uncertainty, even in one of the most well-known, and least variable wood properties for any species. This paper illustrates some of these questions using data collected on spruce from the British Isles.