The Rings

The years pass for everyone, even for trees, which are among the longest-living plants in nature. To find out their age, you need to count their growth rings.

Each passing year forms a ring inside the trunk, in the part below the bark, called the cambium. This is where new wood is created, where the extra ring, the sapwood, is formed: light and thick when it grows in spring, dark and thin when it grows in autumn. Sap flows through its plant cells, a stream of water and mineral salts that rises from the roots immersed in the soil to the leaves distributed on the branches, until air bubbles, which form at the beginning of winter, hinder the flow of these nutrients.

At that point, the sapwood is absorbed by the heartwood, the most valuable part of the wood, which is the thickest part of the trunk and allows the tree, like the skeleton for a human being, to stand upright. This is aged sapwood: hard, compact cells impregnated with phenolic substances that make the heartwood dark and resistant to parasites and where sap no longer flows, but solid wood is extracted. Together with the sapwood, the heartwood constitutes the solid wood that, for the industrial sector, is the only workable part of the trunk necessary to obtain boards and beams, semi-finished products from which manufactured goods will take shape.

But tree rings are much more than a tree's identity card: they are its diary. Just like between the lines of a written page, it is possible to read useful information between the rings of its trunk about the climate changes it has had to endure or the ecological conditions in which it has had to live.

A healthy year for the tree can be read from the thick ring, a thin circle bears witness to dry seasons, while black spots are evidence of fire. Thus, tree rings, linked by the invisible thread of narrative, not only give an account of their current life, but also of events that have occurred around them in the past. They are reliable chroniclers of time, capacious archives of the history of the Earth.