Over half of the world’s forests have been destroyed in the last 10,000 or so years, the majority of this loss has occurred in the last 50 years, occurring simultaneously with a massive increase in the human population. The incredible scale of this loss has led to significant changes throughout many parts of the world, and in recent years these changes have been accelerating. These changes include: large scale extinction events, desertification, climatic changes, topsoil loss, flooding, famine, disease outbreaks, and insect ‘plagues’, among others.

Deforestation occurs primarily due to: agriculture, fuel use (firewood, charcoal, etc), timber, pasture for livestock animals, and expanding human settlements. And also, to a degree, due to large scale war, throughout history fire has often been used as a way to deprive enemy populations of necessary resources. These areas almost always inevitably end up as wastelands via the processes of soil erosion and desertification, if they aren’t reforested. Many of the areas of the world that were deforested thousands of years ago remain as severely degraded wastelands or deserts today.

Currently the world’s annual deforestation rate is estimated to be about 13.7 million hectares a year, that’s about the land area of Greece. Roughly half of this area gets reforested to a degree, though new growth forests don’t function in the same way, support the same biodiversity, nor do they provide the many benefits that old-growth forests do. In addition to these numbers, forests have been becoming more and more affected by climate change, with increasing drought, forest fires, increased and more powerful storms, diseases, and an explosion in insect numbers.

Deforestation Effects, Causes, and Examples: A Top 10 List

1. Agriculture

Agriculture is one of the primary drivers of deforestation, both in modern and ancient times. The vast old growth forests that once covered much of the world have largely been cut and burned down because of agriculture. Even when such agricultural land is reclaimed by nature it generally lacks the great biodiversity that was found there previously, being replaced largely by fast growing plants and ‘weeds’ that favor the depleted soil. Subsistence farming accounts for 48% of deforestation, and commercial agriculture for a further 32% of deforestation, according to United Nations Framework Convention on Climate Change.

Even the most efficient agricultural systems and practices inevitably lead to nutrient loss unless supplemented with fertilizer brought in from elsewhere. And this, along with the soil erosion that accompanies the loss of large vegetation, further contributes to the soil erosion and desertification that seems to almost inevitably follow deforestation in the long term.

2. Population Growth and Expansion

While agriculture is often the direct cause of deforestation, growing and expanding populations are often the driver. The world’s human population has exploded from an estimated max of 15 Million in prehistory to the 7 billion humans of today. Such large population numbers and densities makes people very dependent upon agriculture for survival, and also, importantly, upon expansion. With increased populations also comes increased urbanization, which brings with it further impetus for deforestation, and also negative influences on surrounding areas via pollution.

As large populations often quickly use up all of the resources located near them, they become dependent on expansion to continue fueling their infrastructure, until the distance and the reliance on far off resources becomes too inefficient and the civilization collapses or retracts.

As an example: Western Europe experienced significant deforestation from around 1100 to 1500 as a result of the then rapidly expanding human population. The large industries of the day; the building of wooden sailing ships by European naval powers, colonization and resource plunder dependent on ships, slave trade–and other sea-based trade, largely consumed the forest resources of Europe. This forced governments to seek out these resources further and further from their own seat of power, becoming dependent on these new regions or these resources, before eventually losing their power to these resource producing regions, and collapsing. The newly empowered resource producing region often then follows the same trajectory.

3. Desertification

Desertification is the process by which fertile land is transformed into desert, usually as a result of deforestation, drought, and agriculture use/practices. Desertification played a significant role in the collapse of many large empires and civilizations; such as the Roman Empire, Carthage, the Harappan civilization, and Greece. Most of the desertification that these civilizations experienced was as a result of agriculture, deforestation, and associated changes in aridity and the climate.

The process occurs primarily in dryland ecosystems, which are already very fragile, and simply can’t support the pressures that result from significant human populations. Drylands currently occupy about 40% of the world’s land area. As these lands are cultivated the limited nutrients that are available in them are quickly depleted. Often times the land is also improperly irrigated, leading to salty soils, and emptied aquifers. The limited natural vegetation that is present is also often overgrazed, leading to large-scale soil erosion and increased runoff/decreased rainfall retention.

As a side note, the Sahara is currently expanding south at a rate of up to 48 kilometers per year.

4. Easter Island

Easter Island is the name given to a Polynesian island located in the southeastern Pacific Ocean by the Dutch explorer Jacob Roggeveen in 1722. It’s often referred to as the most remote inhabited island in the world. And is well known for its large stone monuments, called moai. Throughout its history, Easter Island has experienced famine, civil war, slave raids, disease epidemics, colonialism, and nearly complete deforestation, as well as showing signs of agricultural failure and repeated population collapses.

Based on current evidence, the island was likely settled by its current Polynesian inhabitants around 1100 CE, give or take a few hundred years. Owing to the island’s limited land area and relative isolation, large ecological impacts began occurring soon after settlement.

Heavy soil erosion, nearly complete deforestation, wide spread extinctions, and subsequent agricultural failures and a loss of the ability to build seaworthy ships followed the settlement of the island. The final disappearance of the trees on the island seems to coincide exactly with the large-scale decline of its civilization sometime around the 17th or 18th century.

The archeological record clarifies that the current state of the island is vastly different from what it was like at the time of its settlement. Before settlement, the island was nearly entirely forest, with many species of trees that are now extinct there, several of which reached heights of over 50 feet. This includes what would likely be the largest palm tree species in the world if it weren’t extinct, Paschalococos. After the resources started to become more limited the population on the island plummeted to around 2,000–3,000, from a previous high of approximately 15,000. It was during this time that 21 different species of trees, and all of the species of land birds became extinct. This included at least two species of rails, two species of parrots and a heron species.

Researchers think that this was the result of large scale deforestation, overharvesting/overhunting, and the introduction of the rat. As a result of the loss of large trees, the islanders were no longer able to create seaworthy ships. This led to significant changes in their diet, from a previous diet where fish and dolphins provided abundant protein, to one that was almost completely reliant on farming and domesticated chickens.

Previously there had been abundant resources in the large land bird and sea bird populations on the island, these disappeared shortly after the loss of fishing ability, very likely from over exploitation.

As a result of the deforestation, rainfall levels also fell considerably, as there was now far less condensation without the trees there.

“A new style of art from this period shows people with exposed ribs and distended bellies, indicative of malnutrition, and it is around this time that many islanders moved to living in fortified caves and the first signs of warfare and cannibalism appear. Soil erosion because of lack of trees is apparent in some places. Sediment samples document that up to half of the native plants had become extinct and that the vegetation of the island drastically altered. Polynesians were primarily farmers, not fishermen, and their diet consisted mainly of cultivated staples such as taro root, sweet potato, yams, cassava, and bananas. With no trees to protect them, sea spray led to crop failures exacerbated by a sudden reduction in fresh water flows. There is evidence that the islanders took to planting crops in caves beneath collapsed ceilings and covered the soil with rocks to reduce evaporation. Cannibalism occurred on many Polynesian islands, sometimes in times of plenty as well as famine. Its presence on Easter Island (based on human remains associated with cooking sites, especially in caves) is supported by oral histories.”

5. Extinction and Biodiversity Loss

Deforestation has been the cause of a truly massive number of species extinctions in modern times and historical times. Even when the originally deforested area is over time reforested, it always lacks the large biodiversity of its previous state. With the disappearance of the original forest, many species go extinct, and many that don’t lose a great deal of their genetic diversity and variation. This has significant implications for the medical and agricultural industries. Many potential medicines, and disease and pest resistant varieties of agricultural plants, have been lost as a result of deforestation. Modern agriculture is almost entirely dependent on a very limited number of crop plants that are becoming increasingly lacking in genetic diversity, and susceptible to disease, pests, and climatic changes. With the loss of many related wild species, much genetic diversity is lost that could address potential future disease outbreaks and climatic changes.

It’s currently estimated that the world is losing around 137 plant, animal and insect species every day as a result of rainforest deforestation. That’s roughly 50,000 species going extinct every year.

6. Soil Erosion

In ‘undisturbed’ forests there is a very minimal rate of soil loss. Deforestation considerably increases the rate of soil erosion, through the actions of increased rainfall runoff and decreased ground debris. This is further compounded by the increasing aridity of the unprotected soils and the absence of vegetation and roots that work to hold the soil together.

“The decline of the Roman Empire is a story of deforestation, soil exhaustion and erosion,” wrote author Mr. G. V. Jacks. “From Spain to Palestine there are no forests left on the Mediterranean littoral, the region is pronouncedly arid instead of having the mild humid character of forest-clad land, and most of its former bounteously rich top-soil is lying at the bottom of the sea.”

As demand for food and resources increases with a growing population, the land and soil is gradually depleted of nutrients and increasingly experiences erosion. “Regular clearing and plowing exhausted existing soil, which eventually became infertile. Runoff from deforested hillsides increased the amount of silt and impeded the flow of water into agricultural areas. Eventually, due to the Mediterranean climate and the increased depletion of soil nutrients from hundreds of years of harvesting, yields diminished. Rainwater that had been locked into the soil through vegetation and forests was now running off too quickly, with each raindrop unprotected by plants or by a litter layer.”

And while deforestation wasn’t the sole cause the Roman Empire’s fall, when combined with its corollaries of near constant resource based war, declining agricultural productivity, increased disease and epidemics, rebellion, a large degree of urbanization and reliance on complex systems, it contributed very significantly.

7. Atmospheric Change/Greenhouse Effect

Deforestation is having a significant effect on the world’s climate and geography. It is one of the primary contributors to modern climate change. It’s estimated that deforestation currently contributes about 20% of the world’s greenhouse gas emissions directly. Indirectly it contributes significantly by causing carbon dioxide to stay in the atmosphere for longer, rather than being taken up by plants. An estimated 1.5 billion tons of carbon is released every year by tropical deforestation.

Deforestation also has a profound effect on the water cycle. The reduced vegetation cover leads to lower levels of soil and atmospheric moisture. And eventually to soil erosion and desertification. Research done on the deforested north and northwestern regions of China, found that the average annual precipitation there fell by 1/3 between the 1950 and 1980.

8. New Zealand

During the 800 years that New Zealand has been occupied by modern humans about 75% of the original forests have disappeared. At first this was caused by large-scale burning of the forests by Maori and Europeans, but eventually logging became the dominant cause of deforestation there.

As a result of the deforestation many animal species went extinct. Including all of the known species of Moa, a group of giant flightless birds that grew at least as tall as 12 feet and weighed over 500 lbs. The largest eagle known to have ever existed, the Haast’s Eagle, also went extinct. It was a truly massive bird, the largest eagles of today only grow to about half of the size that these birds reached. They were the primary predator of the Moa, and died out roughly when their food sources did. During attack they would have reached speeds of up to 50mph, and delivered the force equivalent of a cinder block falling from an eight story building. There are Maori stories that mention a bird that would occasionally kill humans and steal children.

9. Madagascar

Around 94% of Madagascar’s previously biologically productive lands have been severely degraded by deforestation, resulting in high levels of desertification, greatly decreased water supplies, and high levels of soil loss. Humans are thought to have first settled there about 2000 years ago, since then the island has lost more than 90% of its original forest. A large proportion of this loss has occurred in recent years, and is primarily due to slash-and-burn agriculture. Deforestation has greatly diminished the food resources, soil quality, and fresh water resources available there. Nearly all of Madagascar’s megafauna has gone extinct since human settlement. This includes eight species of giant elephant birds, two species of hippopotamus, a very large species of Fossa, a strange unique mammal named Plesiorycteropus, and seventeen species of lemurs. Lemurs are a type of primate that are exclusive to Madagascar. Many of the lemur species that have already gone extinct were much larger than the species still alive, some growing as large as a male gorilla, such as Archaeoindris fontoynontii. Nearly all remaining species of lemurs are threatened with extinction primarily as a result of deforestation.

10.The Dust Bowl

While recent large scale deforestation wasn’t the primary cause of the Dust Bowl (because there weren’t large scale forests in the region in recent times), it played a significant role.

The Dust Bowl was caused by a combination of poor agricultural practices, drought, and deforestation. Before being converted to farmland the region had been primarily grasslands with some larger vegetation. The limited tree cover that had been present before wide-scale settlement was mostly cut down with settlement. It had functioned to a degree as a natural windbreak and helped to hold together the soil and moisture, along with the deep rooted grasses native to the region. As a result of deep plowing, no use of cover crops, no crop rotation, and no tolerance for ‘weeds’, much of the grass cover that held the soil in place, and trapped moisture, was lost.

“During the drought of the 1930s, without natural anchors to keep the soil in place, it dried, turned to dust, and blew away with the prevailing winds. At times, the clouds blackened the sky, reaching all the way to East Coast cities such as New York and Washington, D.C. Much of the soil ended up deposited in the Atlantic Ocean, carried by prevailing winds. These immense dust storms—given names such as ‘black blizzards’ and ‘black rollers’—often reduced visibility to a few feet or less. The Dust Bowl affected 100,000,000 acres, centered on the panhandles of Texas and Oklahoma, and adjacent parts of New Mexico, Colorado, and Kansas.”