There are many reasons to be thankful for trees. Besides being beautiful and giving shade, they provide habitats for birds, insects and other animals, and they are essential for the production of oxygen, which is vital for life on Earth. 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 trees than there were in the relatively recent past. Since around 10,000 years ago, the planet has lost 2 billion hectares (4.94 billion acres)—from 6 billion hectares (14.83 billion acres) to 4 billion hectares (9.89 billion acres)—of forests. Agriculture, which came about around 12,000 years ago, is the primary reason why one third of Earth’s forests have been lost.

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 area 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, sufficient nutrients, sunlight and adequate rainfall are all important for tree growth. In places where the soil is of poor quality or lacking in nutrients, 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 adequate sunlight or rainfall may be largely devoid of trees. Temperature also matters—most types of trees do not do well in extremely hot areas like deserts or perpetually frozen landscapes. Trees want conditions that are just right.

Even when trees do have the necessary climatic 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), a black insect roughly the size of a grain of rice. This insect has ravaged more than 260,000 square kilometers (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.

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 occurrence in the western United States, the Amazon region of Brazil, Canada and Bolivia. However, these fires are often started by people—sometimes even intentionally by arsonists or farmers clearing land for agriculture. Forestry 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 phenomena affecting forests include landslides, earthquakes and volcanic eruptions. In May of 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 that ripped trees from the ground and scattered them across the landscape.

Human activities take a serious toll on forests. Some forests are clear-cut—completely 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 they grow rapidly and because their resources—wood or fruit, for example—can be harvested and sold. In other cases, clear-cutting is done to make room for grazing livestock. Clear-cutting is occurring in many regions, from the northwestern United States to South America to Africa, and it can be devastating for forest ecosystems in many ways. In addition to being an eyesore, swaths of razed forest are more susceptible to erosion because tree roots are no longer holding the soil in place. Furthermore, clear-cutting reduces the diversity of animals because a large portion of their habitat has been destroyed and they must 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 and palm oil plantations are largely responsible for deforestation in Brazil and Indonesia, respectively.

Clear-cutting is also harmful to the millions of Indigenous people around the globe who live in or near forests, and many of these people rely on forests for their food, shelter and even their livelihoods. Indigenous communities have an outsized effect on forests since they inhabit 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 a mystical connection or an innate sensitivity to the land, but an understanding that their home’s health is tied to their existence. Though Indigenous peoples inhabit these lands, they often lack legal standing or ownership of them. Indigenous communities only have legal rights on about 10% of these lands.

Some of the forests within Indigenous communities are considered sacred by them. These sacred designations lead their respective Indigenous communities to 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.

There is a long history of resistance to deforestation by Indigenous communities. Examples date back hundreds of years. One example is the Asubpeeschoseewagong Anishinabek of Ontario, Canada. Frustrated by government inaction against logging on their lands, the First Nation (also known as Grassy Narrows First Nation) started an ongoing, successful blockade in late 2002.

Another act of Indigenous resistance has happened in Costa Rica. Activists from the Bribri and Bröan communities have occupied settler properties. These were lands promised to them by Costa Rican law. These acts of defiance sometimes resulted in violence against the Indigenous activists and little legal action against the offending settlers.

These Indigenous communities are not alone in trying to limit deforestation. Organizations like Rainforest Alliance, African Wildlife Foundation, Asian Forest Cooperation Organization and Rainforest Trust promote more sustainable land management strategies.

Because trees are not distributed equally around the planet, some regions possess 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 for financial gain. People in those areas also miss out on secondary financial benefits such as 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. It’s also important to 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.