Tree facts for kids

A tree is a large plant that lives for many years. It usually has a single, tall stem called a trunk. This trunk supports many branches and leaves. Some people define trees strictly, only including woody plants that grow very tall. Others include taller palms, tree ferns, bananas, and bamboo in their definition.

Trees are not all from the same plant family. Instead, many different types of plants have independently developed trunks and branches. This helps them grow tall to reach sunlight. Most trees are angiosperms, also known as hardwoods. Many others are gymnosperms, or softwoods. Trees can live for a very long time, with some reaching thousands of years old. The first trees appeared about 400 million years ago. Today, there are an estimated three trillion mature trees worldwide.

A typical tree has many branches held high above the ground by its trunk. The trunk contains woody tissue for strength. It also has vascular tissue to move water and nutrients throughout the tree. Most trunks are covered by bark, which acts as a protective layer. Underground, the roots spread out widely. They anchor the tree and absorb water and nutrients from the soil. Above ground, branches divide into smaller shoots. These shoots usually have leaves. Leaves capture light energy and turn it into sugars through photosynthesis. This process provides food for the tree's growth.

Trees usually make new trees using seeds. Flowering plants keep their seeds inside fruits. Conifers carry their seeds in cones. Tree ferns, however, produce spores instead of seeds.

Trees are very important for our planet. They help reduce soil erosion and control the climate. They take carbon dioxide from the air and store a lot of carbon in their wood. Trees and forests provide homes for many animals and plants. Tropical rainforests are some of the most diverse places on Earth. Trees offer shade and shelter, wood for building, fuel for cooking and heating, and fruit for food. Sadly, forests are shrinking in many parts of the world. This happens as trees are cut down to make more land for farming. Because trees live so long and are so useful, people have always respected them. Many cultures have sacred groves, and trees appear in many mythologies.

What Makes a Plant a Tree?

The word "tree" is common, but there isn't one exact definition. In a general sense, a tree is any plant with a tall stem or trunk. This trunk holds up the leaves and branches high above the ground. Trees are also often defined by their height. Smaller plants, usually between 0.5 to 10 meters (1.6 to 33 feet) tall, are called shrubs. So, the minimum height for a tree is not always clear. Even large plants like papaya and bananas can be called trees in this broad sense.

A more specific definition says a tree has a woody trunk that grows thicker each year. This is called secondary growth. It means the trunk grows outwards, not just upwards from the tip. Under this definition, plants like palms, bananas, and papayas are not considered true trees. This is true even if they are tall. Some monocots, like the Joshua tree, bamboos, and palms, don't have true secondary growth. They don't make wood with growth rings. But they can make "pseudo-wood" by strengthening their cells. Dracaena trees, also monocots, do have secondary growth. However, it's different from the growth in other woody trees.

Sometimes, trees are defined by how we use them. For example, plants that provide lumber (wood for building) are often called trees.

How Trees Grow and Live

The way trees grow tall is an evolutionary adaptation. By growing taller, trees can get more sunlight than other plants. Trees are usually tall and live for a long time. Some can live for thousands of years. Several trees are among the oldest living things on Earth. Trees have special structures like thicker stems. These stems have strong cells that help them grow taller and spread their leaves out. They are different from shrubs, which are usually smaller and have many stems. But there's no strict rule to tell a tree from a shrub. Trees can even be smaller in harsh places like mountains. The tree shape has developed separately in different plant groups. This is a great example of parallel evolution. There are an estimated 60,000 to 100,000 tree species worldwide. This is about 25% of all living plant species. Most of these grow in tropical areas. Many of these regions have not been fully explored by botanists. This means we don't know everything about tree diversity.

Most tree species are angiosperms, also called hardwoods. Many others are gymnosperms, or softwood trees. These include conifers, cycads, ginkgophytes, and gnetales. Gymnosperms have seeds that are not inside fruits. Instead, they are in open structures like pine cones. Many have tough, waxy leaves, like pine needles. Most angiosperm trees are eudicots. Their seeds have two cotyledons, or seed leaves. Some trees are also found among older flowering plants called basal angiosperms. These include Amborella, Magnolia, nutmeg, and avocado. Trees like bamboo, palms, and bananas are monocots.

Wood gives strength to the trunk of most trees. This helps the plant grow larger. The tree's vascular system moves water, nutrients, and other chemicals around the plant. Without it, trees couldn't grow so big. Trees need to pull water high up the stem from the roots. This happens through the xylem by capillary action. Water constantly evaporates from the leaves in a process called transpiration. If there isn't enough water, the leaves will die. The three main parts of a tree are the root, stem, and leaves. They are all connected by the vascular system. In trees that develop wood, the vascular cambium helps the vascular tissue expand. This creates woody growth. Because this growth breaks the outer skin of the stem, woody plants also have a cork cambium. This forms among the phloem. The cork cambium makes thick cork cells to protect the plant's surface and reduce water loss. Both wood and cork production are forms of secondary growth.

Trees are either evergreen or deciduous. Evergreens keep their leaves green all year. Deciduous trees shed their leaves at the end of the growing season. Then they have a resting period without leaves. Most conifers are evergreens. But larches (Larix and Pseudolarix) are deciduous. They drop their needles every autumn. Some cypress species (Glyptostrobus, Metasequoia, and Taxodium) shed small leafy shoots each year. This is called cladoptosis. The crown is the wide top part of a tree, including its branches and leaves. The highest layer in a forest, made by the crowns of trees, is called the canopy. A sapling is a young tree.

Many tall palms are herbaceous monocots. They don't have secondary growth and never produce wood. In many tall palms, only the top bud on the main stem grows. So, they have unbranched trunks with large leaves arranged in a spiral. Some tree ferns, in the order Cyatheales, have tall, straight trunks. They can grow up to 20 meters (66 feet). But these trunks are not made of wood. They are made of rhizomes that grow upwards. These are covered by many adventitious roots.

Where Trees Live Around the World

In 2015, scientists estimated there are 3.04 trillion trees in the world. About 1.39 trillion (46%) are in tropical or sub-tropical areas. Another 0.61 trillion (20%) are in temperate zones. And 0.74 trillion (24%) are in the coniferous boreal forests. This estimate was much higher than previous ones. It was based on tree counts from over 400,000 plots. However, it still has a wide margin of error. This is because most samples came from Europe and North America. The estimate also suggested that about 15 billion trees are cut down each year. Only about 5 billion are planted. Since humans started farming 12,000 years ago, the number of trees worldwide has dropped by 46%. There are about 64,100 known tree species globally. South America has the most diverse tree life, with 43% of all species. Eurasia has 22%, Africa 16%, North America 15%, and Oceania 11%.

In good environments, like the Daintree Rainforest in Queensland, Australia, forests are stable. They are the natural end point of plant growth. Open areas like grasslands are first taken over by taller plants. These then give way to trees, which eventually form a forest.

In cool temperate regions, conifers are often the main type of tree. A common forest type in the far north is the moist taiga, or northern coniferous forest. This is also called boreal forest. Taiga is the world's largest land biome. It covers 29% of the world's forests. The long, cold winter in the far north makes it hard for plants to grow. Trees must grow quickly in the short summer when it's warmer and days are long. Not much light reaches the forest floor under the dense tree cover. So, there might be little plant life, but fungi can be abundant. Similar forests are found on mountains. There, the high altitude makes the average temperature lower, shortening the growing season.

In temperate regions where rain falls evenly throughout the year, you find temperate broadleaf and mixed forest. These forests have trees like oak, beech, birch, and maple. Temperate forests are also in the Southern Hemisphere. For example, in Eastern Australia, you find Eucalyptus forests and open acacia woodlands.

In tropical regions with a monsoon climate, there's a dry season and a wet season. Like in the Amazon rainforest, different broad-leaved trees dominate these forests. Some of these trees are deciduous. In tropical regions with a drier savanna climate, there isn't enough rain for dense forests. The tree canopy isn't closed, so lots of sunlight reaches the ground. This ground is covered with grass and scrub. Acacia and baobab trees are well-suited to live in these areas.

Parts of a Tree

Roots: Anchoring and Feeding the Tree

The roots of a tree hold it firmly to the ground. They also collect water and nutrients to send to all parts of the tree. Roots are also used for making new trees, protecting the tree, storing energy, and other important jobs. The first part of a seedling to grow from a seed is the radicle, or tiny root. This grows into a taproot that goes straight down. After a few weeks, lateral roots branch out sideways. They grow horizontally through the top layers of the soil. In most trees, the taproot eventually disappears, and the wide-spreading lateral roots remain. Near the tips of the smallest roots are tiny, single-celled root hairs. These touch the soil particles directly. They can absorb water and nutrients like potassium that are dissolved in the water. Roots need oxygen to breathe. Only a few species, like mangroves and the pond cypress, can live in soil that is always waterlogged.

In the soil, roots meet tiny threads of fungi called hyphae. Many of these fungi are called mycorrhiza. They form a helpful partnership with tree roots. Some fungi only work with one type of tree. That tree won't grow well without its fungal partner. Other fungi work with many different tree species. The tree gets minerals like phosphorus from the fungus. In return, the fungus gets sugars from the tree's photosynthesis. The fungal threads can even connect different trees. This creates a network that moves nutrients and signals from one tree to another. The fungus helps roots grow and protects trees from pests and diseases. It can also reduce damage from pollution. This is because the fungus can store heavy metals in its tissues. Fossils show that roots have worked with mycorrhizal fungi for 400 million years. This was when the first vascular plants started growing on dry land.

Some trees, like Alder (Alnus species), have a symbiotic relationship with Frankia bacteria. These bacteria can take nitrogen from the air and turn it into ammonia. They live in special bumps on the tree's roots called actinorhizal root nodules. This helps the tree live in places where there isn't much nitrogen in the soil. Plant hormones called cytokinins start the formation of these root nodules. This process is similar to how mycorrhizal partnerships form.

Scientists have shown that some trees are connected through their root systems. They form a kind of colony. These connections happen through a natural process called inosculation. This is like natural grafting or welding of plant tissues. To prove this, scientists inject chemicals, sometimes radioactive ones, into one tree. Then they check if the chemicals appear in nearby trees.

Roots are usually underground. But some tree species have developed aerial roots that grow above the soil. These aerial roots can serve two main purposes. They can help make the tree more stable. They can also get oxygen from the air. For example, the red mangrove grows prop roots. These loop out from the trunk and branches and grow down into the mud. The Indian banyan tree develops a similar structure. Many large trees have buttress roots that spread out from the bottom of the trunk. These roots act like braces, giving the tree stability and reducing swaying in strong winds. They are very common in tropical rainforests. There, the soil is often poor, and roots grow close to the surface.

Some tree species have root extensions that pop out of the soil. These are called pneumatophores. They help the tree get oxygen when there's too much water in the soil. You can see pneumatophores in trees like the black mangrove and pond cypress.

Trunk: The Tree's Strong Support

The main job of the trunk is to lift the leaves high above the ground. This allows the tree to grow taller than other plants and get more sunlight. The trunk also moves water and nutrients from the roots to the upper parts of the tree. It also sends the food made by the leaves to all other parts, including the roots.

In angiosperms and gymnosperms, the outer layer of the trunk is the bark. It's mostly made of dead cells called phellem (cork). Bark provides a thick, waterproof covering for the living tissue inside. It protects the trunk from weather, diseases, animal attacks, and fire. It has many tiny breathing holes called lenticels. Oxygen passes through these holes. Bark is constantly replaced by a living cell layer called the cork cambium. The London plane tree sheds its bark in large flakes. The bark of the silver birch peels off in strips. As a tree grows wider, newer bark layers are larger. In many species, older layers develop cracks. Some trees, like the pine, release sticky resin from their bark to deter attackers. Rubber trees ooze a milky latex. The quinine bark tree has bitter substances in its bark to make it unappetizing. Large tree-like plants like tree ferns, palms, cycads, and bamboos have different trunk structures and outer coverings.

Even though bark protects the tree, it can be attacked by insects like beetles. These beetles lay eggs in cracks. Their larvae then chew through the wood, creating tunnels. This can allow fungal spores to enter and harm the tree. Dutch elm disease is caused by a fungus. It is carried from one elm tree to another by beetles. The tree tries to fight the fungus by blocking the xylem tissue. This tissue carries sap upwards. As a result, the branch above, and eventually the whole tree, dies from lack of nourishment. In Britain in the 1990s, this disease killed 25 million elm trees.

The innermost layer of bark is called the phloem. This layer transports sap containing sugars made by photosynthesis to other parts of the tree. It is a soft, spongy layer of living cells. Some of these cells are arranged end-to-end to form tubes. These are supported by parenchyma cells, which provide cushioning and strengthening fibers. Inside the phloem is a thin layer of cells called the vascular cambium. These cells constantly divide. They create phloem cells on the outside and wood cells, called xylem, on the inside.

The newly created xylem is the sapwood. It is made of water-carrying cells and other living cells. Sapwood is usually light in color. It moves water and minerals from the roots to the upper parts of the tree. The oldest, inner part of the sapwood slowly turns into heartwood. This happens as new sapwood forms at the cambium. In some species, the conducting cells of the heartwood become blocked. Heartwood is usually darker than sapwood. It is the dense center of the trunk that gives it strength. Three-quarters of the dry weight of xylem is cellulose, a type of sugar. Most of the rest is lignin, a complex natural glue. If you look at a cross-section of a tree trunk, you'll see concentric circles of lighter or darker wood. These are annual growth rings. They show how much the tree grew each year. There may also be rays running across the growth rings. These are vascular rays, which are thin sheets of living tissue throughout the wood. Many older trees can become hollow but still stand for many years.

Buds and Tree Growth Cycle

Trees usually don't grow all year long. They have periods of fast growth followed by times of rest. This growth pattern depends on the climate. Growth usually stops when it's too cold or too dry. To prepare for this inactive period, trees form buds. Buds protect the meristem, which is the area of active growth. Before the resting period, the last few leaves at the tip of a twig form scales. These scales are thick, small, and tightly wrapped. They cover the growing tip in a waterproof layer. Inside this bud, there's a tiny stalk and neatly folded miniature leaves. They are ready to open when the next growing season begins. Buds also form where leaves meet the twig. These are ready to produce new side shoots. Some trees, like the eucalyptus, have "naked buds" without protective scales. Some conifers, like the Lawson's cypress, don't have buds. Instead, they have small areas of meristem hidden among their scale-like leaves.

When conditions get better, like warmer weather and longer days in spring, growth starts again. The growing shoot pushes its way out, shedding the scales. These scales leave scars on the twig. All of a year's growth can happen in just a few weeks. The new stem is soft at first and might be green and fuzzy. Palms (Arecaceae) have their leaves arranged in a spiral on an unbranched trunk. In some temperate trees, a second burst of growth, called Lammas growth, can happen. This is thought to help the tree recover if insects ate its early leaves.

Primary growth is when stems and roots get longer. Secondary growth is when tissues get progressively thicker and stronger. The outer layer of the stem turns into bark. The cambium layer creates new phloem and xylem cells. Bark is not stretchy. Eventually, a tree's growth slows down and stops. It won't get any taller. If a tree is damaged, it might become hollow over time.

• 

  Buds, leaves, flowers, and fruit of a pedunculate oak, Quercus robur.

• 

  Buds, leaves, and reproductive parts of a white fir, Abies alba.

• 

  Shape, leaves, and reproductive parts of a queen sago, Cycas circinalis.

• 

  Dormant buds of an ash tree, Fraxinus excelsior.

Leaves: Capturing Sunlight

Leaves are special structures designed for photosynthesis. They are arranged on the tree to get as much light as possible without shading each other. Leaves are a big investment for a tree. They might have thorns or contain chemicals like phytoliths, lignins, tannins, or poisons to stop animals from eating them. Trees have developed leaves in many shapes and sizes. This is in response to things like climate and animals that eat plants. Leaves can be broad or needle-like, simple or compound, lobed or smooth, soft or tough, deciduous or evergreen. The needles of coniferous trees are compact. But they are similar in structure to broad-leaved trees. They are adapted for places with few resources or little water. Frozen ground can limit water. So, conifers are often found in colder places, at higher altitudes, and further north than broad-leaved trees. In conifers like fir trees, the branches hang down. This helps them shed snow.

In contrast, broad-leaved trees in temperate regions handle winter by shedding their leaves. When days get shorter and temperatures drop, leaves stop making new chlorophyll. The red and yellow colors already in the leaves then become visible. The leaf also stops making a plant hormone called auxin. This weakens the cells where the leaf stalk meets the twig. Eventually, the connection breaks, and the leaf falls to the ground. In tropical and subtropical regions, many trees keep their leaves all year. Individual leaves might fall and be replaced by new ones. But most leaves stay on the tree for a long time. Other tropical species and those in dry regions might shed all their leaves annually. This often happens at the start of the dry season. Many deciduous trees flower before their new leaves appear. A few trees don't have true leaves. Instead, they have structures that look similar, like Phylloclades. These are modified stem structures, as seen in the genus Phyllocladus.

Tree Reproduction and Life Cycle

Trees can be pollinated by wind or by animals, mostly insects. Many flowering trees are pollinated by insects. Wind pollination can be more effective high above the ground. Trees use different ways to spread their seeds. Some rely on wind, with winged or feathery seeds. Others rely on animals, for example, with edible fruits. Some trees shoot their seeds out (ballistic dispersal). Others use gravity, so seeds fall and sometimes roll away.

Seeds: Starting New Tree Life

Seeds are the main way trees reproduce. Their seeds come in many sizes and shapes. Some of the largest seeds come from trees. But the largest tree, Sequoiadendron giganteum, produces one of the smallest tree seeds. The great variety in tree fruits and seeds shows how different tree species have evolved to spread their young. For a tree seedling to grow into an adult tree, it needs light. If seeds just fell straight to the ground, many young trees would grow too close. The parent tree's shade would likely stop them from growing well. Many seeds, like those of birch trees, are small and have papery wings. This helps the wind carry them away. Ash trees and maples have larger seeds with blade-shaped wings. These spiral down to the ground when released. The kapok tree has cottony threads that catch the breeze. The flame tree Delonix regia shoots its seeds through the air. This happens when the two sides of its long pods crack open explosively as they dry. The small, cone-like catkins of alder trees produce seeds with tiny oil droplets. These help the seeds float on water. Mangroves often grow in water. Some species have floating fruits with seeds that start growing before they leave the parent tree. These float on the water and can get stuck on new mudbanks, where they successfully take root.

Other seeds, like apple pips and plum stones, have fleshy parts. Smaller fruits like hawthorns have seeds inside edible tissue. Animals like mammals and birds eat these fruits. They either drop the seeds or swallow them. The seeds then pass through their digestive system and are deposited far from the parent tree. The germination of some seeds improves after being processed this way. Nuts might be collected by animals like squirrels. They hide any nuts they don't eat right away. Many of these hidden nuts are never found again. The nut casing softens with rain and frost, and the surviving seeds sprout in the spring. Pine cones can also be hidden by red squirrels. Grizzly bears might help spread seeds by raiding squirrel stashes.

The seeds of conifers, the largest group of gymnosperms, are inside a cone. Most species have light, papery seeds that can be blown far once they are free from the cone. Sometimes, the seed stays in the cone for years. It waits for a special event to release it. Fire can make the seeds of the jack pine release and sprout. Fire also enriches the forest floor with wood ash and removes competing plants. Similarly, some flowering plants, including Acacia cyclops and Acacia mangium, have seeds that sprout better after being exposed to high temperatures. The only living species of Ginkgophyta (Ginkgo biloba) has fleshy seeds. These grow at the ends of short branches on female trees. Gnetum, a tropical group of gymnosperms, produces seeds at the tip of a shoot.

How Trees Have Changed Over Time

The very first trees were tree ferns, horsetails, and lycophytes. They grew in forests during the Carboniferous period. The first tree might have been Wattieza. Fossils of this tree were found in New York state in 2007. They date back to the Middle Devonian period, about 385 million years ago. Before this discovery, Archaeopteris was thought to be the earliest tree. Both of these trees reproduced using spores, not seeds. They are seen as links between ferns and the gymnosperms. Gymnosperms evolved in the Triassic period. They include conifers, cycads, gnetales, and ginkgos. These might have appeared after a major gene duplication event about 319 million years ago. Ginkgophyta was once a widespread group. The only survivor is the maidenhair tree, Ginkgo biloba. This tree is considered a living fossil. It has changed very little from the fossilized trees found in Triassic rocks.

During the Mesozoic Era (245 to 66 million years ago), conifers thrived. They adapted to live in all major land habitats. Later, tree forms of flowering plants evolved during the Cretaceous period. These began to replace conifers during the Tertiary era (66 to 2 million years ago). At that time, forests covered the entire globe. When the climate cooled 1.5 million years ago, the first of four ice ages occurred. The forests retreated as the ice spread. During the warmer periods between ice ages, trees grew back on the land that had been covered by ice. But they were pushed back again in the next ice age.

Trees and Their Environment

Trees are a vital part of Earth's ecosystem. They create important habitats, including many kinds of forests, for communities of living things. Epiphytic plants, like ferns, some mosses, liverworts, orchids, and some parasitic plants (e.g., mistletoe), grow on branches. These, along with tree-dwelling lichens, algae, and fungi, create tiny habitats for themselves and other organisms, including animals. Leaves, flowers, and fruits are available at different times of the year. On the ground beneath trees, there is shade. Often, there is also undergrowth, leaf litter, and decaying wood. These provide other habitats. Trees help stabilize the soil. They prevent rainwater from running off too quickly. They help stop deserts from forming. They play a role in controlling the climate. And they help maintain biodiversity and the balance of ecosystems.

Many tree species support their own special invertebrates. In their natural homes, 284 different insect species have been found on the English oak (Quercus robur). And 306 invertebrate species live on the Tasmanian oak (Eucalyptus obliqua). Non-native tree species usually support fewer different kinds of life. For example, in the United Kingdom, the sycamore (Acer pseudoplatanus), which came from southern Europe, has few associated invertebrate species. However, its bark supports many lichens, mosses, and other epiphytes. Trees differ in how easily herbivores can find them. This depends on a tree's size, its chemical content, and how much it's hidden by other plants from its insect pests.

In ecosystems like mangrove swamps, trees help create the habitat. The roots of mangrove trees slow down tidal currents. They trap sediment carried by the water. This reduces the water depth and creates good conditions for more mangroves to grow. So, mangrove swamps tend to expand towards the sea in suitable places. Mangrove swamps also provide a strong barrier against the damaging effects of cyclones and tsunamis.

How We Use Trees

Food from Trees

Trees give us many of the world's most popular fruits. Apples, pears, plums, cherries, and citrus fruits are grown commercially in temperate climates. A wide variety of edible fruits are found in tropical regions. Other important commercial fruits include dates, figs, and olives. Palm oil comes from the fruits of the oil palm (Elaeis guineensis). The fruits of the cocoa tree (Theobroma cacao) are used to make cocoa and chocolate. The berries of coffee trees, Coffea arabica and Coffea canephora, are processed to get coffee beans. In many rural areas, people gather fruit from forest trees to eat. Many trees also produce edible nuts. These are usually large, oily kernels inside a hard shell. Examples include coconuts (Cocos nucifera), Brazil nuts (Bertholletia excelsa), pecans (Carya illinoinensis), hazel nuts (Corylus), almonds (Prunus dulcis), walnuts (Juglans regia), and pistachios (Pistacia vera). Nuts are very nutritious. They contain high-quality protein, vitamins, minerals, and dietary fiber. Many nut oils are pressed for cooking. Some, like walnut, pistachio, and hazelnut oils, are valued for their unique flavors. However, they tend to spoil quickly.

In temperate climates, sap moves quickly through trees at the end of winter. This happens as trees get ready to grow. In North America, the sap of the sugar maple (Acer saccharum) is used to make maple syrup. About 90% of the sap is water. The other 10% is a mix of sugars and some minerals. Sap is collected by drilling holes in tree trunks. The liquid flows out of inserted spigots. The sap is then heated to concentrate its flavor. Similarly, in northern Europe, the spring sap of the silver birch (Betula pendula) is tapped and collected. It can be drunk fresh or fermented into an alcoholic drink. In Alaska, the sap of the sweet birch (Betula lenta) is made into syrup. This syrup has a 67% sugar content. Sweet birch sap is more watery than maple sap. One hundred liters of sap are needed to make one liter of birch syrup.

Different parts of trees are used as spices. Cinnamon comes from the bark of the cinnamon tree (Cinnamomum zeylanicum). Allspice is made from the dried small fruits of the pimento tree (Pimenta dioica). Nutmeg is a seed found in the fleshy fruit of the nutmeg tree (Myristica fragrans). Cloves are the unopened flower buds of the clove tree (Syzygium aromaticum).

Many trees have flowers rich in nectar. These flowers attract bees. Making forest honey is an important industry in rural areas of developing countries. Small-scale beekeepers use traditional methods. The flowers of the elder (Sambucus) are used to make elderflower cordial. Plum (Prunus spp.) petals can be candied. Sassafras oil is a flavoring. It is made by distilling bark from the roots of the sassafras tree (Sassafras albidum).

Tree leaves are widely gathered as food for livestock. Some can be eaten by humans. However, they often contain high levels of tannins, which make them bitter. Leaves of the curry tree (Murraya koenigii) are eaten. Those of kaffir lime (Citrus × hystrix) are used in Thai food. Ailanthus leaves are used in Korean dishes like bugak. Leaves from the European bay tree (Laurus nobilis) and the California bay tree (Umbellularia californiana) are used for flavoring food. Camellia sinensis, the plant that gives us tea, is a small tree. But it is usually heavily pruned to make picking its leaves easier.

Wood smoke can be used to preserve food. In hot smoking, food is exposed to smoke and heat in a controlled way. The food is ready to eat when finished. It becomes tender and flavored by the smoke. In cold smoking, the temperature stays below 38 °C (100 °F). This enhances the food's flavor, but the raw food still needs cooking. If meat is to be preserved, it should be cured before cold smoking.

Wood for Fuel

Wood has been used as fuel for a very long time, especially in rural areas. In less developed countries, it might be the only fuel available. Collecting firewood often takes a lot of time. People have to travel further and further to find it. It is often burned inefficiently in open fires. In more developed countries, other fuels are available. Burning wood is often a choice, not a necessity. Modern wood-burning stoves are very efficient. New products like wood pellets are also available for burning.

Charcoal can be made by slowly heating wood without air. This process is called pyrolysis. It happens in a special oven called a kiln. Carefully stacked branches, often oak, are burned with very little air. Turning them into charcoal takes about fifteen hours. Charcoal is used as fuel for barbecues and by blacksmiths. It also has many industrial and other uses.

Timber: Wood for Building and More

Timber refers to "trees grown to produce wood." This wood is cut into lumber (sawn wood) for construction. Wood has been an important and easily available building material since humans started making shelters. Engineered wood products are also available. These bind wood particles, fibers, or veneers together with glue to form composite materials. Plastics have replaced wood for some traditional uses.

Wood is used to build buildings, bridges, pathways, poles for power lines, boat masts, mine supports, railway sleepers, fences, and scaffolding. In housebuilding, it's used for joists, roof trusses, roofing shingles, staircases, doors, window frames, floorboards, and wall panels.

Wood is also used to make carts, farm tools, boats, canoes, and ships. It's used for furniture, tool handles, boxes, ladders, musical instruments, bows, weapons, matches, clothes pegs, brooms, shoes, baskets, carvings, toys, pencils, barrels, coffins, skis, and sports equipment.

Wood is pulped to make paper. It's also used to make cardboard and engineered wood products for construction. Examples include fiberboard, hardboard, chipboard, and plywood. Wood from gymnosperms is called softwood. Wood from angiosperms is called hardwood.

Trees as Art

Trees have inspired artists for centuries. They have also been used to create art themselves. Living trees are shaped in bonsai and tree shaping. Both living and dead trees have been sculpted into amazing forms.

Bonsai: Miniature Trees

Bonsai (盆栽, lit. "Tray planting") is the art of growing and shaping small trees. It started in China as penjing and came to Japan over a thousand years ago. Other cultures have similar practices, like the miniature landscapes of Vietnam called hòn non bộ. The word bonsai is often used for all miniature trees grown in containers.

The main goals of bonsai are for people to enjoy looking at them and for the grower to enjoy the effort and creativity. Bonsai involves long-term care and shaping of one or more small trees in a container. It starts with a cutting, seedling, or small tree. Almost any tree or shrub that lives for many years and has woody stems can be used. They must produce true branches and can be kept small by growing them in pots and pruning their tops and roots. Some species are popular for bonsai because they have small leaves or needles. These features make them perfect for the compact look of bonsai. You can even create a miniature forest using trees like Japanese maple, Japanese zelkova, or hornbeam.

Tree Shaping: Living Sculptures

Tree shaping is the practice of changing living trees and other woody plants into human-made shapes. These can be for art or for useful structures. There are a few ways to shape a tree. One is a gradual method. This slowly guides the growing tip along planned paths over time. Another is an instant method. This bends and weaves young trees, 2 to 3 meters (6.6 to 9.8 feet) long, into a shape. This shape becomes stronger as the trees grow thicker. Most artists use grafting to join living trunks, branches, and roots. This creates art or functional structures. There are even plans to grow "living houses." The branches of trees would knit together to form a solid, weatherproof outside. The inside would be covered with straw and clay to create a smooth surface.

Tree shaping has been done for at least several hundred years. The oldest known examples are the living root bridges. These were built and maintained by the Khasi people of Meghalaya, India. They used the roots of the rubber tree.

Bark: A Tree's Protective Skin

Cork comes from the thick bark of the cork oak (Quercus suber). It is harvested from living trees about once every ten years. This is an environmentally friendly industry. More than half of the world's cork comes from Portugal. It is mostly used to make stoppers for wine bottles. Other uses include floor tiles, bulletin boards, balls, footwear, cigarette tips, packaging, insulation, and parts of woodwind instruments.

The bark of other oak varieties has traditionally been used in Europe for tanning animal hides. Bark from other tree species has been used elsewhere. The active ingredient, tannin, is extracted. After some preparation, the skins are soaked in solutions of increasing strength. The tannin makes the hide soft, less affected by water, and more resistant to bacteria.

At least 120 medicines come from plants. Many of these come from tree bark. Quinine comes from the cinchona tree (Cinchona). For a long time, it was the main treatment for malaria. Aspirin was created to replace sodium salicylate. This came from the bark of willow trees (Salix), which had unpleasant side effects. The anti-cancer drug Paclitaxel comes from taxol. This substance is found in the bark of the Pacific yew (Taxus brevifolia). Other tree-based medicines come from the paw-paw (Carica papaya), the cassia (Cassia spp.), the cocoa tree (Theobroma cacao), the tree of life (Camptotheca acuminata), and the downy birch (Betula pubescens).

The papery bark of the paper birch (Betula papyrifera) tree was used a lot by Native Americans. Wigwams were covered with it, and canoes were built from it. Other uses included food containers, hunting and fishing gear, musical instruments, toys, and sleds. Today, bark chips, which are a leftover from the timber industry, are used as mulch. They are also used as a growing medium for epiphytic plants that need soil-free compost.

Ornamental Trees: Beauty in Landscapes

Trees create a visual impact, just like other landscape features. They give parks and gardens a sense of age and permanence. People grow them for their beautiful shapes, leaves, flowers, fruit, and bark. Where they are placed is very important for creating a landscape. They can be grouped informally, often with bulbs planted around them. They can be arranged in grand avenues or used as single, special trees. As living things, their appearance changes with the seasons and from year to year.

Trees are often planted in towns, where they are called street trees or amenity trees. They provide shade and cooling through evapotranspiration. They absorb greenhouse gases and pollutants. They also catch rainfall and reduce the risk of flooding. Scientific studies show that street trees help cities be more sustainable. They also improve the physical and mental well-being of people living there. It has been shown that trees help people feel good and reduce stress. Many towns have started tree-planting programs. For example, in London, there's a plan to plant 20,000 new street trees. They also aim to increase tree cover by 5% by 2025, which is like one tree for every resident.

Other Uses of Trees

Latex is a sticky liquid that plants use to defend themselves against animals that eat them. Many trees produce it when injured. But the main source of latex for natural rubber is the Pará rubber tree (Hevea brasiliensis). Originally, it was used to make bouncy balls and waterproof cloth. Now, natural rubber is mainly used in tires, where synthetic materials have not been as durable. The latex from the balatá tree (Manilkara bidentata) is used to make golf balls. It is similar to gutta-percha, which comes from the "getah perca" tree Palaquium. Gutta-percha was also used as an insulator, especially for undersea cables, and in dentistry, walking sticks, and gun butts. It has now mostly been replaced by synthetic materials.

Resin is another liquid that trees release. It also helps with defense. It's a thick liquid mostly made of volatile terpenes. Coniferous trees produce most of it. Resin is used in varnishes, for making small castings, and in ten-pin bowling balls. When heated, the terpenes evaporate, and the remaining product is called "rosin." Stringed instrument players use rosin on their bows. Some resins contain essential oils and are used in incense and aromatherapy. Fossilized resin is known as amber. Most amber formed in the Cretaceous period (145 to 66 million years ago) or more recently. Resin that oozed out of trees sometimes trapped insects or spiders. These are still visible inside the amber.

The camphor tree (Cinnamomum camphora) produces an essential oil. The eucalyptus tree (Eucalyptus globulus) is the main source of eucalyptus oil. This oil is used in medicine, as a fragrance, and in industry.

Threats to Trees

Protecting Individual Trees

Dead trees can be dangerous, especially during strong winds and storms. Removing dead trees costs money. Healthy trees, however, can clean the air, increase property values, and cool down built areas. This reduces building cooling costs. During dry times, trees can suffer from lack of water. This can make them more likely to get diseases and insect problems. Ultimately, it can lead to a tree's death. Watering trees during dry periods can reduce the risk of water stress and death.

Tree Conservation Efforts

About one-third of all tree species, around twenty thousand, are on the IUCN Red List of Threatened Species. Of these, over eight thousand are globally threatened. At least 1,400 of them are classified as "critically endangered."

Amazing Tree Records!

Tallest Trees

Scientists in the UK and Malaysia have found the world's tallest tropical tree, which is more than 100 meters (328 feet) high!

A redwood tree in Redwood National Park, California, was measured at 115.85 meters (380 feet) tall, making it the tallest known tree.

The tallest trees in Australia are all types of eucalypts. There are over 700 species of eucalypts! The 'mountain ash' eucalypt, with its slim, straight trunk, can grow to over 300 feet tall.

Stoutest Trees

The widest living single-trunk tree is the African baobab. One baobab in South Africa, called the Glencoe baobab, was measured at 15.9 meters (52 feet) across near the ground! This tree split in 2009, so now the stoutest baobab might be the Sunland Baobab in South Africa, which is 10.64 meters (34.9 feet) wide.

Some trees can grow many trunks that join together. The sacred fig is a great example. It grows new 'trunks' from its branches that reach the ground and get thicker. A single sacred fig tree can have hundreds of these trunks!

Oldest Individual Trees

The age of trees is usually found by counting their growth rings. This works best for trees in places with seasons. Trees in tropical climates often grow all the time and don't have clear rings. Also, some very old trees become hollow inside as their old heartwood decays, making it hard to count rings.

Here are some of the oldest trees whose ages have been confirmed:

• Great Basin bristlecone pine (Methuselah) Pinus longaeva: 4,844 years old
• Alerce: 3,622 years old
• Giant sequoia: 3,266 years old
• Sugi: 3,000 years old
• Huon-pine: 2,500 years old

Other trees thought to be very old include the European Yew (possibly over 2,000 years) and western redcedar. The oldest known European yew is the Llangernyw yew in North Wales, estimated to be between 4,000 and 5,000 years old!

The oldest known flowering plant tree is the Sri Maha Bodhi sacred fig (Ficus religiosa). It was planted in 288 BC in Sri Lanka and is said to be the oldest human-planted tree with a known planting date, making it 2,293 years old.

Oldest Forests

The very first fossilized trees found are from 386 million years ago, in the Devonian period. They were discovered in an old quarry in Cairo, New York. This ancient forest was so huge it stretched beyond Pennsylvania!

This discovery is two or three million years older than the previous oldest forest found at Gilboa, also in New York State.

Trees in Culture

Trees have always been important symbols in different cultures. Common ideas include the World tree, like Yggdrasil, and the tree of life. Trees are often used to represent nature or the environment itself. A common mistake is thinking that trees get most of their weight from the ground. Actually, 99% of a tree's weight comes from the air!

Wishing Trees

A Wish Tree is a special tree, often chosen because of its type, location, or how it looks. People use it to make wishes and leave offerings. These trees are seen as having a special religious or spiritual meaning. Traditionally, people make offerings to these trees, hoping that a nature spirit, saint, or goddess will grant their wish.

Tree Worship

Tree worship means that many societies throughout history have worshipped or created myths about trees. Trees have played a very important role in many of the world's mythologies and religions. They have been given deep and sacred meanings for ages. People see how trees grow and die, how flexible their branches are, and how their leaves change and come back every year. Because of this, trees are powerful symbols of growth, decay, and resurrection. The oldest symbol across many cultures for how the universe is built is the 'world tree'.

World Tree

A tree, with its branches reaching up to the sky and roots deep into the earth, can be seen as living in three worlds. It connects heaven, the earth, and the underworld, joining what's above with what's below. It's also a symbol of both feminine (giving life) and masculine (strong) qualities – another union.

Because of this, many myths around the world have the idea of a World tree. This is a huge tree that acts as an Axis mundi (a central point of the world), holding up the cosmos and linking the heavens, earth, and underworld. In European mythology, the most famous example is the tree Yggdrasil from Norse mythology.

The world tree is also a big part of Mesoamerican myths. There, it represents the four main cardinal directions (north, south, east, and west). The idea of the world tree is also closely connected to the idea of the Tree of life.

In Literature

In books and stories, a famous mythology about trees was created by J.R.R. Tolkien. His Two Trees of Valinor are very important in his 1964 book Tree and Leaf. William Butler Yeats also writes about a "holy tree" in his poem The Two Trees (1893).

List of Trees

There are many types of trees. Here is a list of some of them:

• Apple tree
• Coconut palm
• Cottonwood
• Eucalyptus
• Fir
• Horse chestnut
• Mangrove
• Maple
• Oak
• Palm
• Pine
• Redwood
• Rubber tree
• Willow
• Yew
• Birch

Related Pages

• Wattezia is the earliest tree found in old rock records.

Images for kids

• 

  Branches and twigs.

• 

  Beech leaves

• 

  Tree roots anchor the structure and provide water and nutrients. The ground has eroded away around the roots of this young pine tree

• 

  Growth rings. The dark lines between the center and the bark are medullary rays, which allow nutrients to flow across the tree trunk

• 

  Common ash (Fraxinus excelsior), a deciduous broad-leaved (angiosperm) tree

• 

  Diagram of secondary growth in a eudicot or coniferous tree showing idealised vertical and horizontal sections. A new layer of wood is added in each growing season, thickening the stem, existing branches and roots.

• 

  Tall herbaceous monocotyledonous plants such as banana lack secondary growth, but are trees under the broadest definition.

• 

  The Daintree Rainforest

• 

  Conifers in the Swabian alps

• 

  A section of yew (Taxus baccata) showing 27 annual growth rings, pale sapwood and dark heartwood

• 

  Buds, leaves, flowers and fruit of oak (Quercus robur)

• 

  Form, leaves and reproductive structures of queen sago (Cycas circinalis)

• 

  Dormant Magnolia bud

• 

  Wind dispersed seed of elm (Ulmus), ash (Fraxinus) and maple (Acer)

• 

  Lepidodendron, an extinct lycophyte tree

• 

  Sugar maple (Acer saccharum) tapped to collect sap for maple syrup

• 

  Selling firewood at a market

• 

  Roof trusses made from softwood

• 

  Trees in art: Weeping Willow, Claude Monet, 1918

• 

  Informal upright style of bonsai on a juniper tree

• 

  People trees, by Pooktre

• 

  Recently stripped cork oak (Quercus suber)

• 

  Alleé of London plane trees (Platanus × acerifolia) in garden

• 

  Latex collecting from a rubber tree (Hevea brasiliensis)

• 

  Yggdrasil, the World Ash of Norse mythology

• 

  The General Sherman Tree, thought to be the world's largest by volume

See also

In Spanish: Árbol para niños

• Agroforestry
• Arboretum
• da Vinci branching rule
• Dendrology
• Dendrometry
• Exploding tree
• Five Trees
• Forest restoration
• Fruit tree
• Great Green Wall (Africa)
• i-Tree
• Lists of trees – a list of all Wikipedia's lists of trees
• Million Tree Initiative
• Multipurpose tree – grown for multiple outputs
• Reforestation
• Tree climbing
• Tree credits
• Tree house
• Tree line
• Tree planting bar
• Tree planting
• Trillion Tree Campaign
• Urban forest
• Urban forestry
• Urban reforestation