Talkative wood
Alder comes across as bulbous and cosy, maple elegant and with long curves, while oak tends towards the dramatic with its particularly contrasting texture: Wood patterns – as the grain is also known – are individual and characterful pieces that can bring either life or disquiet into the home on ceilings, walls, floors or furniture. How expressive the respective wood picture turns out is fundamentally and clearly dependent on the individual biography of the tree providing the boards. But not only that: depending on which side and from which angle the trunk is cut, different textures result, in which the annual rings are more clearly or more discreetly visible or the naturally conical growth of the trees becomes visible.
Hardening takes time
The natural play of colour shades as well as line thicknesses and gradients fascinates the untrained eye, just as it informs the eye of wood specialists at a glance about the quality, slate formation, splitting and behavioural tendencies of the wood in the event of changing temperature and humidity conditions: Evenly grown wood is less likely to warp than wood that has been exposed to a constant change of good and bad years. You can also tell at first glance whether the wood is hardwood or softwood. This is because hardwoods such as walnut or oak grow more slowly than spruce and the like, and their annual ring lines are correspondingly finer and narrower.
History and
climate research on wood
Dendrochronology is another scientific discipline that deals professionally with wood grain: The sum of the annual rings is the entire history of the tree, in which the local climatic conditions of its lifetime are inscribed as well as traumas caused by mechanical injuries, pest infestations or forest fires that leave scars in the wood tissue. Dendrochronology systematically utilises these histories by using wood samples from different eras to create annual ring calendars spanning several thousand years, which in turn add up to an overall picture of local, regional and global climate development. With the help of the right tree-ring calendar, the age and material origin of wooden structures or artefacts can be determined fairly accurately. And it was dendroarchaeology, which is closely related to dendrochronology, that provided proof of a long-held assumption: that a series of sun-darkening volcanic eruptions during the reign of the Eastern Roman Emperor Justinian led to dramatic cooling, which in turn was partly responsible for the Justinianic Plague.
The annual rings, which are so characteristic in cross-section, are formed by two things: the growth of trees in thickness and the change of seasons or supply conditions (such as rainy and dry seasons) or temperature levels. The tissue layer called cambium is responsible for the growth in thickness. The first annual ring is formed when the cambium ring grows by secreting earlywood inwards and bast outwards (which forms the bark of the tree). The earlywood is characterised by large and thin-walled cells, making it mechanically unstable.
The soft tissue lignifies through the incorporation of solid biopolymers called lignin, becomes firmer and turns into dense and darker latewood. The same pattern continues: in the growth phase after the winter rest period or during dry periods, the tree forms earlywood, which transforms into latewood. The more favourable the climatic conditions of a year are for the tree, the more earlywood it produces – and the wider the annual ring becomes.