Yet we often treat trees as disposable: as something to be harvested for economic gain or as an inconvenience in the way of human development. Since our species began practicing agriculture around 12,000 years ago, we’ve cleared nearly half of the world’s estimated 5.8 trillion trees, according to a 2015 study published in the journal Nature.
Much of the deforestation has happened in recent years. Since the onset of the industrial era, forests have declined by 32%. Especially in the tropics, many of the world’s remaining three trillion trees are falling fast, with about 15 billion cut each year, the Nature study states. In many places, tree loss is accelerating. In August, the National Institute for Space Research showed an 84% increase in fires in the Brazilian Amazon rainforest compared to the same period in 2018. Slash-and-burn is also especially on the rise in Indonesia and Madagascar.
For starters, if trees disappeared overnight, so would much of the planet’s biodiversity. Habitat loss is already the primary driver of extinction worldwide, so the destruction of all remaining forests would be “catastrophic” for plants, animals, fungi and more, says Jayme Prevedello, an ecologist at Rio de Janeiro State University in Brazil. “There would be massive extinctions of all groups of organisms, both locally and globally.”
The wave of extinctions would extend beyond forests, depleting wildlife that depends on single trees and small stands of trees as well. In 2018, Prevedello and his colleagues found, for example, that overall species richness was 50 to 100% higher in areas with scattered trees than in open areas. “Even a single, isolated tree in an open area can act as a biodiversity ‘magnet,’ attracting and providing resources for many animals and plants,” Prevedello says. “Therefore, losing even individual trees can severely impact biodiversity locally.”
The planet’s climate would also be drastically altered in the short and long term. Trees mediate the water cycle by acting as biological pumps: they suck water from the soil and deposit it into the atmosphere by transforming it from liquid to vapour. By doing this, forests contribute to cloud formation and precipitation. Trees also prevent flooding by trapping water rather than letting it rush into lakes and rivers, and by buffering coastal communities from storm surges. They keep soil in place that would otherwise wash away in rain, and their root structures help microbial communities thrive.
Without trees, formerly forested areas would become drier and more prone to extreme droughts. When rain did come, flooding would be disastrous. Massive erosion would impact oceans, smothering coral reefs and other marine habitats. Islands stripped of trees would lose their barriers to the ocean, and many would be washed away. “Removing trees means losing huge amounts of land to the ocean,” says Thomas Crowther, a global systems ecologist at ETH Zurich in Switzerland and lead author of the 2015 Nature study.
In addition to mediating the water cycle, trees have a localised cooling effect. They provide shade that maintains soil temperatures and, as the darkest thing in the landscape, they absorb heat rather than reflect it. In the process of evapotranspiration, they also channel energy from solar radiation into converting liquid water into vapour. With all of those cooling services lost, most places where trees formerly stood would immediately become warmer. In another study, Prevedello and his colleagues found that complete removal of a 25 sq km patch of forest caused local annual temperatures to increase by at least 2C in tropical areas and 1C in temperate areas. Researchers have also found similar temperature differences when comparing forested and open areas.
On a global scale, trees combat warming caused by climate change by storing carbon in their trunks and removing carbon dioxide from the atmosphere. Deforestation already accounts for 13% of total global carbon emissions, according to an IPCC report published in August, while land use change in general accounts for 23% of emissions. With all trees on the planet wiped out, previously forested ecosystems “would become only a source of emission of carbon dioxide into the atmosphere, rather than a sink,” says Paolo D'Odorico, a professor of environmental science at the University of California, Berkeley.
Large amounts of carbon would run into the oceans, causing extreme acidification and killing possibly everything but jellyfish.
Humanity’s suffering would begin well before catastrophic global warming took place, however. The increased heat, disruption to the water cycle and loss of shade would take a deadly toll on billions of people and livestock. Poverty and death would also descend on many of the 1.6 billion people who currently rely directly on forests for their livelihoods, including for harvesting food and medicine. More people still would find themselves unable to cook or heat their homes, given the lack of firewood. Around the world, those whose work revolves around trees – whether as loggers or paper-makers, fruit growers or carpenters – would suddenly be jobless, devastating the global economy. The timber sector alone provides employment to 13.2 million people and generates $600bn (£500bn) each year, according to the World Bank.
All told, human beings would struggle to survive in a world without trees. Urbanised, Western lifestyles would quickly become a thing of the past and many of us would die from starvation, heat, drought and floods. Surviving communities, Lowman believes, would likely be those that have retained traditional knowledge about how to live in treeless environments, such as Australia’s Aboriginals. Crowther, on the other hand, suspects that life would only persist in a Mars-like colony, enabled by technology and entirely divorced from the existence we have always known.
