The Growth and Structure of Wood
We’re going to go back to basics and start a series of articles all about wood, without which you wouldn’t be using your framing nailer.
The tree is truly unique in the plant kingdom both in terms of its size and also its incredible longevity.
There are over 44,000 known species of trees ranging from the Alaskan dwarf pine at a paltry 1m through to the colossal 120m high California redwood.
Some trees can live for thousands of years.
We’ll start out today by looking at some key elements of the growth and structure of this magnificent natural material.
Structure of Wood
The outermost layer of the tree is called bark.
The core function of this bark is to protect the inner tissue from extremes of temperature. It can also help to protect the tree against some diseases.
The inner bark is called phloem. The role of this inner bark is to conduct the synthesized food from the leaves on throughout the rest of the tree. It also serves to facilitate gaseous exchanges.
This is the actual growing layer of the tree.
A thin and delicate tissue, the cambium is responsible for the production of new wood. This happens in both directions, outwards toward the phloem and inwards to the sapwood.
Thanks to the cambium, the tree trunk becomes more substantial along with the branches for the duration of the growing season. This season extends throughout spring and summer in temperate areas.
The sapwood is distinguishable from the main part of the tree – the heartwood – since it’s paler in color.
The chief function of the sapwood is to conduct mineral salts from the roots of the tree to the leaves.
The sapwood can reach up to 2 inches wide and even wider still in some tropical species.
The heartwood is found within the sapwood.
Made up of dead cells, the heartwood gives support, stability and also stores food.
Most timber comes from the heartwood.
The medulla or pith lies at the center of the heartwood. Although it’s usually invisible to the naked eye, you can just about make out the pith in a few species.
The cambium or growing layer has annual growth rings to correspond with the age of the tree.
Disease or drought can wreak havoc with the growth of a tree. In these instances, the growth rings become quite narrow.
Some More Facts About Trees
Trees are no different from other plants in that they depend on photosynthesis to produce new cells and to grow.
The growing points of a tree are known as the primary meristems and they are responsible for the height of the tree. They can be found at the tip of the trunk and also on each branch and twig.
When it comes to increasing the girth of the tree, the cambium (secondary meristems) produce new sapwood and phloem throughout the growing season. This new wood is laid down in the form of growth rings.
The study of the way in which trees grow is dendrochronology. This can provide us with a highly accurate record of environmental conditions in addition to the biological incidents in a tree’s life (as well as any trauma).
The heartwood, as the name would suggest, is at the very center of the tree. Oils and resins are found in the heartwood along with latex, gums and dyes. Most of these are extracted when the tree is felled. Latex, though, is tapped from living trees.
The color of the wood is affected by some of the gums and resins inside.
Mineral deposits, on the other hand, can lead to hard or soft patches in the wood which is not such good news.
Most trees grow in pretty much the same way but they can be divided roughly into distinct classifications…
Conifers or Gymnosperms
These more primitive trees are cone-bearing with needle leaves. They are also known as softwoods.
These trees can be further divided into two…
- Monocotyledons: Palms and grasses are included in this classification of tree. This means that they hold little interest for most woodworkers
- Dicotyledons: These broad-leaved deciduous trees are also referred to as hardwoods.
It should be noted that the terms softwood and hardwood are botanical terms which do not reflect the actual physical properties of the tree. Many softwoods have far harder wood than hardwoods making it really rather confusing!
Texture of Wood
Trees have extremely varied patterns of growth and this becomes evident when we examine the huge range of wood textures.
Even-textured wood generally means that there is little contrast between wood produced at the beginning of the growing season – this is known as earlywood – or the latewood that occurs later on.
When there is a more marked contrast, the wood tends to have a much more uneven texture.
When wood is described, the texture is often differentiated as either fine textured or coarse textured. It’s the size of the cells and the width of the rays that make up this distinction in texture. Large cells and wide rays lead to coarse textured wood while fine textured has small cells and thin rays.
We hope you have found this glance at the make-up of trees and the way in which they grow to be useful and informative.
Get in touch if you have any queries at all or if there is anything you would like us to cover on this new site. We will be attempting to cover all aspects of wood not just tools and hope that as the site grows, this will become a handy reference point for you in terms of all aspects of woodworking.
We always welcome feedback and respond to any email as quickly as we can.
Come back for more in our series on the mechanics of wood with plenty of framing nailers for you to choose from when it comes to taking on woodworking projects commercially or at home.