Rainforests around the world still continue to fall. Does it really make a difference? Why should anyone care if some plants, animals, mushrooms, and microorganisms perish? Rainforests are often hot and humid, difficult to reach, insect-ridden, and have elusive wildlife.
Actually the concern should not be about losing a few plants and animals; mankind stands to lose much more. By destroying the tropical forests, we risk our own quality of life, gamble with the stability of climate and local weather, threaten the existence of other species, and undermine the valuable services provided by biological diversity.
While in most areas environmental degradation has yet to reach a crisis level where entire systems are collapsing, it is important to examine some of the effects of existing environmental impoverishment and to forecast some of the potential repercussions of forest loss. Continuing loss of natural systems could make human activities increasingly vulnerable to ecological surprises in the future.
The most immediate impact of deforestation occurs at the local level with the loss of ecological services provided by tropical rainforests and related ecosystems. Such habitats afford humans valuable services such as erosion prevention, flood control, water filtration, fisheries protection, and pollination—functions that are particularly important to the world's poorest people, who rely on natural resources for their everyday survival. Forest loss also reduces the availability of renewable resources like timber, medicinal plants, nuts and fruit, and game.
Over the longer term, deforestation of tropical rainforests can have a broader impact, affecting global climate and biodiversity. These changes are more challenging to observe and forecast from local effects, since they take place over a longer time scale and can be difficult to measure.
Deforestation for rubber in Laos. Click image for more pictures. (Photo by R. Butler)
Deforestation for rubber in Laos. Click image for more pictures. (Photo by R. Butler)
Local and regional consequences of deforestation
The local level is where deforestation has the most immediate effect. With forest loss, the local community loses the system that performed valuable but often under-appreciated services like ensuring the regular flow of clean water and protecting the community from flood and drought. The forest acts as a sort of sponge, soaking up rainfall brought by tropical storms while anchoring soils and releasing water at regular intervals. This regulating feature of tropical rainforests can help moderate destructive flood and drought cycles that can occur when forests are cleared.
When forest cover is lost, runoff rapidly flows into streams, elevating river levels and subjecting downstream villages, cities, and agricultural fields to flooding, especially during the rainy season. During the dry season, such areas downstream of deforestation can be prone to months-long droughts which interrupt river navigation, wreak havoc on crops, and disrupt industrial operations.
Situated on steep slopes, montane and watershed forests are especially important in ensuring water flow and inhibiting erosion, yet during the 1980s, montane forests suffered the highest deforestation rate of tropical forests. (That trend changed in the late 1990s and 2000s, when upland forests recovered, while lowland areas bore the brunt of deforestation, largely due to agricultural expansion).
A satellite image showing a heart-shaped island of forest in Indonesian Borneo.
Additionally, the forest adds to local humidity through transpiration (the process by which plants release water through their leaves), and thus adds to local rainfall. For example, 50-80 percent of the moisture in the central and western Amazon remains in the ecosystem water cycle. In the water cycle, moisture is transpired and evaporated into the atmosphere, forming rain clouds before being precipitated as rain back onto the forest. When the forests are cut down, less moisture is evapotranspired into the atmosphere resulting in the formation of fewer rain clouds. Subsequently there is a decline in rainfall, subjecting the area to drought. If rains stop falling, within a few years the area can become arid with the strong tropical sun baking down on the scrub-land. Today Madagascar is largely a red, treeless desert from generations of forest clearing with fire. River flows decline and smaller amounts of quality water reach cities and agricultural lands. The declining rainfall in interior West African countries has in part been attributed to excessive clearing of the coastal rainforests. Similarly, new research in Australia suggests that if it were not for human influences—specifically widespread agricultural fires—the dry outback might be a wetter, more hospitable place than it is today. The effect of vegetation change from forests that favor rainfall to grassland and bush can impact precipitation patterns. Colombia, once second in the world with freshwater reserves, has fallen to 24th due to its extensive deforestation over the past 30 years. Excessive deforestation around the Malaysian capital of Kuala Lumpur, combined with the dry conditions created by el Niño, triggered strict water rationing in 1998, and for the first time the city had to import water.
There is serious concern that widespread deforestation could lead to a significant decline in rainfall and trigger a positive-feedback process of increasing desiccation for neighboring forest cover; reducing its moisture stocks and its vegetation would then further the desiccation effect for the region. Eventually the effect could extend outside the region, affecting important agricultural zones and other watersheds. At the 1998 global climate treaty conference in Buenos Aires, Britain, citing a disturbing study at the Institute of Ecology in Edinburgh, suggested the Amazon rainforest could be lost in 50 years due to shifts in rainfall patterns induced by global warming and land conversion.
The newly desiccated forest becomes prone to devastating fires. Such fires materialized in 1997 and 1998 in conjunction with the dry conditions created by el Niño. Millions of acres burned as fires swept through Indonesia, Brazil, Colombia, Central America, Florida, and other places. The Woods Hole Research Center warned that more than 400,000 square kilometers of Brazilian Amazon were highly vulnerable to fire in 1998. That extent grew in 2005 and 2010 when the Amazon was hit by even worse droughts.
River in the Peruvian Amazon. (Photo by R. Butler)
Erosion in Madagascar. (Photo by R. Butler)
Soil erosion and its effects
The loss of trees, which anchor the soil with their roots, causes widespread erosion throughout the tropics. Only a minority of areas have good soils, which after clearing are quickly washed away by the heavy rains. Thus crop yields decline and the people must spend income to import foreign fertilizers or clear additional forest. Costa Rica loses about 860 million tons of valuable topsoil every year, while the Great Red Island, Madagascar, loses so much soil to erosion (400 tons/ha) that its rivers run blood-red, staining the surrounding Indian Ocean. Astronauts have remarked that it looks like Madagascar is bleeding to death, an apt description of a country with grave environmental degradation and an agriculture-reliant economy that depends on its soils. The rate of increase for soil loss after forest clearing is astonishing; a study in Ivory Coast (Cote d'Ivoire) found that forested slope areas lost 0.03 tons of soil per year per hectare; cultivated slopes annually lost 90 tons per hectare, while bare slopes lost 138 tons per hectare.
After heavy tropical rains fall on cleared forest lands, the run-off carries soil into local creeks and rivers. The rivers carry the eroded soils downstream, causing significant problems. Hydroelectric projects and irrigation infrastructure lose productivity from siltation, while industrial installations suspend operations due to lack of water. Siltation also raises river beds, increasing the severity of floods, and creates shoals and sandbars that make river navigation far more troublesome. The increased sediment load of rivers smothers fish eggs, causing lower hatch rates. As the suspended particles reach the ocean, the water becomes cloudy, causing regional declines in coral reefs, and affecting coastal fisheries. The loss of coral reefs worldwide, often labeled the rainforests of the sea, is especially dist
