There are many reasons to be thankful for trees. Besides being beautiful and giving shade, they provide habitats for animals, and they are essential for the production of oxygen, which is vital for life on Earth. Trees, and other plants, take carbon dioxide from the air and use it for biomass through the process of photosynthesis. By taking carbon dioxide out of the atmosphere, trees lower temperatures. Additionally, they supply important products like wood, paper, fruit and nuts. The livelihoods of more than 1.5 billion people worldwide—about 20% of the global population—depend on trees.

Unfortunately, trees are not present everywhere—only about one-third of Earth's surface is forested. And there are far fewer than in the relatively recent past. Since about 10,000 years ago the planet has lost one-third of its forests. Agriculture, which came about around 12,000 years ago, is the primary cause of this loss.

Forests tend to fall into one of three types based on their location: boreal, temperate and tropical. Boreal forests are located the farthest north, temperate forests grow in the midlatitudes and tropical forests are found closer to the Equator. Countries with the largest forested areas include Russia, Canada, Brazil, China and the United States.

Forests are concentrated in particular places because trees, like other plants, require specific conditions to thrive. Fertile soil, nutrients, sunlight and rainfall are all important for tree growth. In places where the soil is poor, tree growth may be stunted or not occur at all. For instance, trees atop mountains are typically much smaller than those at lower elevations, because soils tend to be poorer on steep slopes. Likewise, places that do not receive much sunlight or rainfall typically have few trees. Temperature also matters—most types of trees do not do well in extremely hot areas like deserts or in frozen landscapes. Trees want conditions that are just right.

Even when trees do have the necessary conditions, they can be hurt by natural processes such as pest infestations. One serious pest, for instance, is the mountain pine beetle (Dendroctonus ponderosae Hopkins). This insect has destroyed more than 100,000 square miles of forest in the western United States and Canada. The mountain pine beetle kills trees by clogging the trees' connective tissues.

Trees Face a Number of Threats

Another threat to forests is fire. Lightning strikes from thunderstorms can set entire forests ablaze, and heavy winds can quickly spread a fire. Forest fires have become an increasingly frequent problem in the western United States, the Amazon region of Brazil, Canada and Bolivia. They are often started by people—sometimes even intentionally. Experts point out that fires have always been part of the natural cycle in forests. However, as drought and high temperatures have become more common, forest fires are becoming larger and more dangerous.

Less common problems affecting forests include landslides, earthquakes and volcanic eruptions. In May 1980, the explosive eruption of Mount St. Helens in the U.S. state of Washington sent out a shockwave that toppled thousands of trees and stripped others of their branches. The eruption also triggered a series of volcanic mudflows. They ripped trees from the ground and scattered them across the landscape.

Human activities take a serious toll on forests. Some forests are cut down for timber, to make room for new trees, or to simply clear the land for another purpose. When new trees are planted, they are often selected because their resources—wood or fruit, for example—can be harvested and sold. In other cases, forests are cut down to make room for livestock. Clear-cutting happens when an entire area of forest is cut down. It is occurring in many regions, and it can be devastating for forest ecosystems. Swaths of razed forest are more likely to experience erosion because tree roots are no longer holding the soil in place. Furthermore, clear-cutting reduces the diversity of animals by destroying habitat and forcing animals to flee to find new shelter.

An especially devastating type of clear-cutting is deforestation, during which trees are not replanted. Deforestation occurs mostly to make land available for agriculture. About half of all tropical deforestation happens in just two nations: Indonesia and Brazil. Cattle ranching is largely responsible for deforestation in Brazil, while palm oil plantations are largely responsible for deforestation in Indonesia.

Clear-cutting is also harmful to the millions of Indigenous people around the globe who live in or near forests. Many of these people rely on forests for their food, shelter and even their livelihoods. Indigenous communities have an especially large effect on forests since they live in about 40% of Earth’s remaining forests. Studies have shown they protect these lands more effectively than non-Indigenous peoples. The reasons for this are not magic, but an understanding that their home’s health is tied to their well-being. Though Indigenous peoples inhabit these lands, they often lack legal standing or ownership of those lands.

Some forests within Indigenous communities are considered holy by them. Because of this, Indigenous peoples act as caretakers for these forest landscapes. Examples include Ethiopia’s church forests, Thailand’s De Paw Thoo (umbilical) forest to the Karen people and the Greek groves of Zagori and Konitsa.

Trees are not distributed equally around the planet. Some regions have more forest resources than others, and this inequality has important economic and social effects. To begin with, in areas that lack forests, there are no forest products to be harvested and sold. People in those areas also miss out on secondary benefits. They miss out on revenue from tourism and fees from hunters going after large game animals like deer and moose. Aside from financial considerations, forests serve as cool and calming refuges for people as well as animals.

Earth’s forests need all the help they can get. One way to help is by reducing paper use and other single-use products. Learn what companies use sustainable methods and buy from them, not companies with careless or harmful environmental policies. Finally, speak up for the rights of Indigenous communities.