Wood

Wood comes from trees and shrubs.

It is very strong. This strength helps trees grow tall. It also helps them stand up.

Inside a tree, wood works like a straw. It carries water to the leaves. It also moves food around.

Trees grow new layers every year. These layers make rings. You can see these rings on a log.

Sometimes, a dead branch makes a knot.

Knots can change how the wood looks.

People have used wood for a long time. We use it to build houses. We also use it for paper and tools.

Wood is a strong material found in trees and shrubs.

It is made of tiny fibers called cellulose. These fibers are held together by a glue called lignin. This glue helps the wood resist being squeezed.

In a living tree, wood helps the plant stand up tall. It also works like a straw to move water and food.

Trees grow wider each year through secondary growth. This happens when new layers form inside the bark. In many places, this creates growth rings. You can see these rings on a cut log.

The rings are often wider in the spring. This part is called earlywood. The wood made later in the season is called latewood.

Most wood starts as sapwood. This is the outer part that carries water. As the tree gets older, the center changes. It becomes heartwood. This wood is darker and resists decay.

You might also see knots in the wood. A knot forms when a branch dies and gets covered. Knots can make the wood look interesting or change its strength. People have used wood for thousands of years. We use it for fuel, houses, and even paper.

Wood is a natural material found in the stems and roots of many plants.

It is a composite material made of three main parts. Tiny fibers called cellulose provide strength when the wood is pulled. These fibers sit inside a matrix of lignin and hemicelluloses. Think of lignin as a natural glue that holds the fibers together. This glue helps the wood resist being squeezed or compressed. In a living tree, wood acts as support so the plant can grow tall.

It also works like a system of pipes to move water and nutrients.

Trees grow wider through a process called secondary growth.

This happens because of cell division in a layer called the vascular cambium. This layer adds new woody layers between the existing wood and the inner bark. In many places, this creates visible growth rings. The rings are often wider in the early part of the season. This lighter part is called earlywood or springwood. The wood formed later in the season is called latewood or summerwood.

If the seasons are not very different, these rings might be hard to see.

Humans have used wood for thousands of years. We use it for fuel, building houses, and making tools. Ancient hunters even used wooden spears with tips toughened by fire. By 15,000 BC, people used wooden spear-launchers to throw weapons further. In Neolithic Europe, people built longhouses out of wood. Scientists can even use wood to study the past. They use carbon dating or dendrochronology to find when an object was made.

This helps us learn about the climate from a long time ago.

Wood has a very long history on Earth.

A discovery in New Brunswick, Canada, found plants with wood from 395 to 400 million years ago. Today, wood is a very important resource for the world. In 2020, the total stock of forests was about 557 billion cubic meters. In 2023, people harvested almost 4 billion cubic meters of wood. About half of that was used as fuel, like wood or charcoal. The rest was used for building and making furniture.

Inside a tree, you will find different types of wood.

Most wood starts as sapwood, which is the outer, living part. Sapwood carries water from the roots to the leaves. As the tree ages, the center changes into heartwood. Heartwood is darker and resists decay better than sapwood.

You might also see knots in the wood. A knot forms when the base of a branch is covered by new wood. Knots can change how strong the wood is. However, many people like them because they look beautiful in furniture.

Wood is a complex structural tissue found in the stems and roots of trees and other woody plants.

Scientifically, wood is defined as xylem, which is the tissue responsible for transport and support. It is a natural composite material made of three organic polymers. Cellulose fibers provide strength when the material is pulled, known as tension. These fibers are embedded in a matrix of lignin and hemicelluloses. Lignin acts as a natural glue that holds the cellulose fibers together. This matrix allows the wood to resist compression, or being squeezed. In a living tree, wood provides the mechanical support needed to grow large. It also functions as a system to convey water and nutrients between the roots and the leaves.

Trees increase their diameter through a process called secondary growth.

This process begins with cell division in the vascular cambium. The vascular cambium is a lateral meristem, which is a layer of tissue that allows for growth in width. As these cells divide and expand, they form thickened secondary cell walls. This new wood is added between the existing wood and the inner bark. In regions with distinct seasons, this growth creates visible annual rings. The part of the ring formed early in the season is called earlywood or springwood. It is usually wider and lighter in color. The later part of the ring is called latewood or summerwood.

In equatorial regions like Singapore, these rings may be indistinct due to consistent growth.

Within the trunk, wood is divided into two main functional zones: sapwood and heartwood.

All wood begins its life as sapwood, also known as alburnum. Sapwood is the younger, outermost layer of wood. In a living tree, its principal function is to conduct water from the roots to the leaves. It also stores and releases nutrient reserves. As the tree ages, the inner wood undergoes a genetically programmed chemical transformation. This creates heartwood, or duramen. Heartwood is often darker and more resistant to decay than sapwood. While the term "heartwood" suggests it is vital, a tree can actually thrive even if its heartwood decays. The amount of sapwood in a tree is often proportional to the size of its crown.

As a tree grows, it may develop knots, which are considered imperfections in the wood.

A knot forms when the base of a branch or a dormant bud becomes overgrown by the trunk. Subsequent layers of wood envelop the branch, enclosing it within the stem. When a tree is sawn into boards, these knots may appear as dark, circular shapes. Within a knot, the grain direction can be up to 90 degrees different from the rest of the wood. Knots can reduce the tension strength of a plank, which affects how much weight it can hold. However, they do not always affect stiffness or resistance to compression. In many decorative applications, such as furniture, knots are actually valued for their visual interest.

Humans have utilized wood for thousands of years for a vast array of purposes.

It has served as fuel, a construction material, and a source for tools and weapons. Known constructions using wood date back ten thousand years. In Neolithic Europe, people built large longhouses primarily from wood. Early hunters even crafted spears from wood, sometimes toughening the tips with fire. By 15,000 BC, humans were using wooden spear-launchers to increase force and distance. Today, wood is also used as a feedstock to produce purified cellulose. This material is used to create products like cellophane and cellulose acetate.

Wood science is the formal discipline used to study these materials.

Scientists can use wood to reconstruct the history of our planet. For example, dendrochronology is the study of tree rings to determine the age of wooden objects. The width of these rings and their isotopic abundances provide clues about past climates. A discovery in New Brunswick, Canada, revealed plants that grew wood approximately 395 to 400 million years ago. This shows that wood-producing plants have existed for hundreds of millions of years. By studying the patterns in wood, researchers can understand environmental changes over long periods of time.

Wood remains a massive and significant global resource.

As of 2020, the global growing stock of forests was approximately 557 billion cubic meters. In 2023, nearly 4 billion cubic meters of wood were harvested. About half of this harvested wood is used for fuel, such as fuelwood, charcoal, or pellets. The other half is used for building construction and furniture. Because it is an abundant and carbon-neutral renewable resource, wood is of intense interest for renewable energy. This makes wood a vital component in modern discussions about sustainable materials and global ecosystems.