Trees have played an important role in our lives for centuries – in fact, there probably wouldn’t be life on Earth without them. The air we breathe comes from the ability trees have to absorb carbon dioxide and provide oxygen. Trees provide us with food, they give us materials to make tools and even to build our homes with.
There are two types of tree: conifers and deciduous species. Most conifers are evergreens and are most common in colder climates. With the exception of the larch, evergreen trees retain their leaves all year round. In temperate or polar climates, deciduous trees lose their leaves in the autumn, so that they can save energy over the winter. In other areas of the world, such as tropical, subtropical and arid regions, deciduous trees lose their leaves during the dry season, or during other seasons depending on variations in rainfall.
The trinity of the tree
All trees are made up of three parts: the roots, the trunk and the crown. The task of the roots is to provide the tree with water and minerals from the ground, store nutrients and keep the tree ‘rooted’ in the ground. The crown is made up of branches or twigs bearing leaves or needles. The task of the crown is to use the leaves for the “metabolism” of the tree, photosynthesis. Meanwhile, the task of the trunk is to hold up the crown and transport water from the roots to the crown. On a hot summer day, as much as one cubic metre of water can be transported to the crown. The trunk is made up of cellulose and lignin, which make it hard. This hardness and durability makes wood an incredibly useful material from which to craft floors, build houses and furniture, tools and toys, and many other things.
Pith and rings determine the appearance
The outer part of the trunk is known as the sapwood and it is normally paler than the heartwood. However, there are exceptions to this, such as spruce. The sapwood part of the trunk contains a lot of fluid. The heartwood is the inner part of the trunk and it’s normally darker than the sapwood because the cells contain resins and fats, etc. Birch and beech have no pronounced heartwood and are, therefore, known as sapwood trees.
The heartwood consists of dead cells and it has a lower moisture content than the sapwood. Part of the trunk is made up of what is known as the pith. The pith contains stored nutrients. Nutrients are transported to and from the pith through the trunk by means of cells known as pith rays. All wood species have pith rays. The pith rays in oak and ash are clearly visible, but in beech they can’t be seen at all.
In the spring, when the tree begins to grow, spring wood is formed. Its large, thin-walled cells give the tree the best possible conditions for growth. In the summer, the tree grows more slowly and forms the smaller, thick-walled cells that form the load-bearing part of the trunk. This process takes place during every growing season, making the tree thicker and creating new annual rings. The width of these rings varies between different species and growing conditions. Deciduous trees have more summer wood than conifers, which means that deciduous trees are usually denser.
Wood: an ideal material for flooring
Wood is a wonderfully useful and versatile material, in many ways. For example, it has very good thermal properties. In older buildings, solid wood was even used to provide insulation.
- Wood is anisotropic; it has different properties in different directions, e.g. when it absorbs or loses moisture.
- Wood is also heterogeneous, which means that its different parts have different properties. Spring wood is not the same as summer wood, and wood from branches isn’t the same as wood from the trunk.
- Wood is hygroscopic, it adjusts its moisture content to the relative humidity of the ambient air.
- Wood is also rheological, which means that it can change shape under a sustained load, and it can change colour over time.
Wood expands and contracts in all three directions. The anisotropic and hygroscopic properties of wood are of the greatest importance when it comes to floor manufacturing. This is why Kährs patented multi-layer design is so successful. The anisotropic nature of the wood counteracts the wood's hygroscopic nature simply, but brilliantly.