Forests

A large area of land covered with trees or other woody vegetation.

How do you define a forest? A forest is a complex community of life in which trees are the dominant life form. They can also have a huge population of other woody plant life. Forests cover 31% of the earth's land surface. They are found on every continent except Antarctica, with about 50% of forest area found in five countries: Russia, Brazil, Canada, the United States, and China. Forests have been and continue to be important for many reasons.

Why are forests important? Healthy forests filter water, remove air pollution, absorb carbon, and provide homes for wildlife and plants. In fact, they are home to almost 80% of Earth's land animals and plants. Forests prevent soil erosion and play a role in climate control. They are places of beauty and recreation, and they provide food, fuel, and medicine for people all over the world. Perhaps most importantly, forests produce large amounts of oxygen that we need to breathe.

Forests are made up of three growth layers. Each layer provides different types of habitat for different kinds of wildlife. The thick top layer is called the canopy. This is where the tops of the trees meet to form a thick “umbrella” that often does not allow much sunlight to reach the layers underneath.

The layer just below the canopy is known as the understory. Here smaller trees and bushes live. They receive little light due to the canopy. However, when gaps form in the canopy, understory trees may take advantage of the opening and grow taller. Shrubs, bushes, and brambles grow where enough light passes through the canopy to support their growth.

The forest floor is the third and lowest layer of the forest. Here you can find grasses, ferns, wildflowers, mosses, and other small plants that grow close to the ground and can thrive without much sunlight. Many of these ground covers provide food for forest animals. New tiny trees that have started from dropped seeds may or may not grow to maturity, depending on the amount of sun and rain that reaches them through the canopy and understory. The forest floor itself is often covered with decaying leaves and twigs. Here, fungi, insects, and bacteria break down dead material and recycle them into rich soil.

Forests belong to different biomes, depending upon the climate where they grow. The world's land biomes are classified by the primary kind of vegetation that grows in a given climate. The three main forest biomes on Earth, labeled by type of forest, are tropical rainforest, temperate forest, and boreal forest. Temperatures, amounts of rainfall, and types of plants and animals are different for each type of forest. You can learn more about the forests of the world at The Forest Biome.

Tropical rainforests occur near the equator, in warm, wet regions called the tropics. The temperature doesn't vary much throughout the year. Vegetation in rainforests is dense, lush, and very green. Rainforests receive between 80-400 inches of rain each year. In some forests, it rains every day. In fact, in a number of rainforests, rain is generated from the plants themselves in the humid environment as it cycles around and around. Some of the rain may never reach the ground but will lay on the leaves of the understory.

The top layer in the rainforest, above the canopy, is called the emergent layer. Giant trees grow here that thrust up taller than the trees below. The canopy is composed of the crowns of broadleaf trees that make a dense, continuous cover. Thick vines climb up and through the trees, reaching for sunlight. The understory and forest floor are quite dark since little sunlight reaches these layers.

Rainforests cover just 6% of the world's land surface, but they are home to more than half the world's plants and animals. There is a great diversity of life in rainforests, with more types of trees than in any other area of the world and hundreds of species of birds, reptiles, mammals, and insects. Typical animals of the rainforest are monkeys, macaws, snakes, frogs, butterflies, sloths, and bats. Insects are the largest group of inhabitants in the rainforest. Scientists believe there may be millions of plant and insect species in rainforests yet to be identified.

Learn more about tropical rainforests at Blue Planet Biomes

Temperate forests occur in eastern and western North America, northeastern Asia, and western and central Europe. These areas have four seasons including winter, but do not have extreme temperatures.

Many temperate forests consist of deciduous trees, such as maple, ash, oak, hickory, elm, and beech. Each fall, these trees change color and then lose their leaves as they fall to the ground. New leaves grow in the spring. Temperate deciduous forests have rich, fertile soils, receive abundant rainfall, and provide a home for many species of forest animals including squirrels, deer, bears, foxes, raccoons, rabbits, skunks, and many birds and insects. Other temperate forests are composed of evergreens, such as spruce, pine, and fir. Temperate evergreens are coniferous trees, with needles instead of leaves. They do not lose their needles, which have a special waxy coating to protect them in winter. In all temperate forests, wildlife must be able to adapt to changing seasons.

Expansive deciduous forests once covered most of the eastern half of what is now the United States, from northern New England to central Florida, and west to the Mississippi River. Much of this temperate forest was cut down long ago to clear land for crops and cities. In the western United States, temperate coniferous forests are found in mountain regions. Coniferous forests are usually cooler and drier than deciduous forests.

Learn more about temperate forests at Ask A Biologist or NASA.

Boreal forests, also known as taiga, occur between 50° and 60° north latitudes. Boreal forests can be found across northern Asia, northern Europe, Canada, and Alaska. Taiga is the Earth's largest land habitat, covering about 17% of our planet's land and about 27% of all forested areas. Summers are short, moist, and moderately warm. Winters are long, cold, and snowy. The average temperature is below freezing for six to eight months of the year.

There are fewer species of plants and animals in boreal forests due to the harsh winter conditions. The soils tend to be poor in nutrients because the rate of decomposition is so slow. Boreal forests are filled with evergreen trees such as hemlock, fir, pine, and spruce. The trees tend to be thin and to grow close together to provide protection from the wind and cold. The waxy needles help reduce water loss, and the trees' upside-down cone shape allows heavy snow to slide off and prevents branches from breaking.

Typical animals of the taiga include lynx, otters, hawks, mink, weasels, wolves, and snowshoe hares. Many species of birds migrate to the taiga in the summer to nest and feed on the abundant insects but leave before winter comes.

Learn more about boreal forests at Ask a Biologist or Biomes of the World.

Idaho has 21.5 million acres of forest land, covering 40% of the state's total area. Idaho's forests are a treasured natural resource with many uses. 86% of Idaho forests are owned and managed by government agencies: the United States Forest Service (76%), the Bureau of Land Management (4%), and the State of Idaho (6%). Idaho has a greater percentage of land dedicated to national forests than any other state. Learn more about each of the eleven national forests in Idaho.

Idaho's forests are primarily found in mountain regions. These forests are largely characterized as temperate coniferous forests. Idaho's state tree, the Western White Pine, is found in the forests of northern Idaho. A few deciduous trees, such as aspen or birch, can also be found in Idaho's forests. Forests are found at altitudes where snowpack and rain feed the roots sufficient moisture to sustain these giant life forms. A 100-foot-tall tree requires more than 11,000 gallons of water in one growing season. This water is recycled back into the environment when the tree releases oxygen and water vapor.

Learn more about Idaho's forests.

Forestry is the science of forest management. Most countries have forest management agencies to help monitor and protect their natural forests. In the United States, the top priority of the United States Forest Service is to “maintain and improve the health, diversity, and productivity of forests.” Some of the tasks of forestry include collecting forest data, restoring ecosystems, reducing hazards, and managing forests for all types of uses — from recreation to timber harvesting.

In the past, forests were viewed by many people as primarily timber to be cut down to use as fuel or building material, or as obstacles to be burned or cleared away so that the land could be farmed. But today, forests are managed to balance environmental and human needs, both now and in the future. Sustainable forestry means that as trees are harvested for wood products, they are replaced by seedlings that will grow into mature trees. A well-managed forest will contain trees of different ages and often different species. In sustainable forestry, care is taken to conserve wildlife habitat, protect water quality, and ensure ecosystem health. The goal is for forests to be continually renewed for the future.

People who work in forestry are called foresters. They are scientists and technicians who work to keep forests healthy and productive. Foresters plan and carry out forestry projects, such as planting new trees, conserving wildlife habitat, assessing timber plots for harvesting, monitoring trees for disease, and supervising reforesting efforts. Meet some foresters and find out about their careers in forestry.

Forests face many challenges. One of the most well-known threats is wildfire. Fire can destroy the lives and homes of forest plants and animals and cause billions of dollars in damage. Natural fires have always been part of forest ecosystems, and in some cases ground fires clear out the forest floor to allow for more sunlight and growth. However, in recent years climate change has led to hotter, drier conditions that have resulted in larger and more destructive wildfires. It can take a very long time for a forest to recover from a fire. Learn more at the Science Trek Wildfire site.

Another threat to forests is harmful insects and diseases. Just like animals and people, trees can get sick, and the disease can spread from tree to tree in forests. Many forest diseases are caused by fungi that weaken and kill trees. Insect pests like gypsy moths and bark beetles destroy millions of trees every year. Trees that are weakened from drought or fire damage are more prone to insects and disease. A large part of modern forest management deals with efforts to protect trees from such threats.

Other threats to forests include acid rain, which results when pollutants from industrial smoke mix with rainfall, and non-native invasive species, which can endanger forests when species that do not belong there are introduced and take over natural species.

Deforestation, where forests are destroyed and not replanted, is a major, human-caused problem in many areas of the world. While forests once covered about half of Earth's surface, today they cover less than one-third. Just in the last 30 years, our planet has lost about a billion acres of forest. Up to half of the world's rainforest has been lost. Much of this rainforest land has been cleared away to make room for ranching, farming, and mining or for unsustainable logging operations. Boreal forests are also currently threatened by overlogging. Deforestation not only destroys wildlife habitat but also increases the risk of soil erosion and flooding and contributes to global warming.

More people and governments are realizing how important it is to conserve forest land through sustainable forest management, where trees are harvested in a way that protects the future of the forest. Many regions are engaged in large reforestation projects and in increasing the amount of protected forest area. The need to balance the needs of the environment, wildlife, and humans will continue.

• Forests produce oxygen that we need to breathe. Forests are sometimes called the “lungs of the planet.” Through photosynthesis, trees release oxygen through their leaves and needles. One large tree can provide a day's oxygen for four people!
• Forests absorb carbon from the atmosphere. Carbon dioxide is a “greenhouse gas” that contributes to global climate change. As trees grow, they take in carbon dioxide and store it as carbon in their trunks, roots, and branches. Scientists estimate that forests absorb nearly 40% of fossil-fuel emissions. Learn more about how carbon capture by forests benefits the Earth.
• Forests help clean the air of pollution by filtering and absorbing chemicals and particles in the air.
• Forests play an important part in the water cycle. They help store, cleanse, and filter the water that flows through them. More than one-third of Earth's largest cities get much of their drinking water from protected forests.
• Forests cool our planet by providing shade. They are like natural air conditioners as they cool the air and ground around them. Close to cities, urban forests can cool the air by up to 8 degrees, reducing energy usage.
• Forests help to moderate rainfall, which also keeps temperatures cooler. Trees absorb water and release it into the atmosphere. Water then collects into clouds and is released again as rain. In some places, more than 50% of rainfall originates from the trees of the forest.
• Forests prevent soil erosion by anchoring the soil with their roots. This prevents soil loss during heavy rainstorms and windstorms. The root systems also break up the soil, allowing for better water drainage and storage. Forests keep soil from drying out and help make it more fertile by adding decaying organic matter and large numbers of microbes to the soil.
• Forests provide homes for 80% of land animals and plants. Many species of animals depend on forest habitats for shelter, food, safety, and space. Some kinds of plants and animals live in only a certain part of the forest and cannot survive elsewhere. Forests support biodiversity – a great variety of different forms of life.
• Forests provide many types of foods that humans eat, including berries, nuts, fruits, mushrooms, spices, herbs, and maple syrup.
• Forests provide wood that is processed into lumber for constructing buildings, furniture, fences, and much more. Wood pulp is used to make paper, books, cardboard boxes, tissues, and paper towels.
• Forests produce a renewable energy source. People burn wood as fuel for warming homes, cooking food, and producing steam.
• Forests produce life-saving medicines. More than 25% of medications we use come from forests. These include medicines to treat cancer, malaria, and heart disease. Scientists have only studied a small number of forest plants for possible medical uses.
• Forests provide opportunities for recreation. People come to forests to camp, hike, hunt, fish, watch wildlife and explore nature.
• Forests are good for people's mental health. They block noise, reduce stress, and create a peaceful, relaxing environment that makes people feel happier.

Forests provide so many benefits to keep our planet healthy. A healthy forest is a natural resource that provides habitat, products, and ecosystem services to a wide variety of life forms, including human beings. It is important to take care of forests so that they will be around for future generations of people and wildlife to enjoy and use.

Learn more about the trees that make up forests at Science Trek's website on Trees.