Deforestation: The conversion of forest to another land use or the long-term reduction of the tree canopy cover below a 10 percent threshold. Deforestation implies the long-term or permanent loss of forest cover and its transformation into another land use.
People have been deforesting the Earth for thousands of years, primarily to clear land for crops or livestock.
Annual change in forest area by region in millions of hectares per year, 1990-2010. There is a continued trend towards expansion in Europe, while large-scale afforestation in China of between 2 and 3 million hectares per year is contributing to net gains in Asia. The rate of deforestation is decreasing in some countries, such as Brazil and Indonesia. However, net losses remain significant in South America and Africa despite this reduction. Severe drought and forest fires have exacerbated forest losses in Australia since 2000. Source: FAO (2010)
Direct causes of deforestation are agricultural expansion, wood extraction (e.g., logging or wood harvest for domestic fuel or charcoal), and infrastructure expansion such as road building and urbanization. Rarely is there a single direct cause for deforestation. Most often, multiple processes work simultaneously or sequentially to cause deforestation.
The world’s total forest area is just over 4 billion hectares, corresponding to 31 percent of the total land area or an average of 0.6 ha per capita. The five most forest-rich countries (the Russian Federation, Brazil, Canada, the United States of America and China) accounted for more than half of the total forest area. Ten countries or areas had no forest at all and an additional 54 had forest on less than 10 percent of their total land area.
At present the rate of deforestation and loss of forest from natural causes is still alarmingly high, but is slowing down. At the global level, it decreased from an estimated 16 million hectares per year in the 1990s to around 13 million hectares per year in the last decade.
At the same time,
afforestation and natural expansion of forests in some countries and areas
reduced the net loss of forest area significantly at the global level. The
net change in forest area in the period 2000–2010 was estimated at -5.2
million hectares per year (an area about the size of Costa Rica), down
from -8.3 million hectares per year in the period 1990–2000. However, most
of the loss of forest continued to take place in countries and areas in
the tropical regions, while most of the gain took place in the temperate
and boreal zones, and in some emerging economies.
Impacts of Deforestation: Biodiversity Impacts
Although tropical forests
cover only about 7 percent of the Earth’s dry land, they probably harbor
about half of all species on Earth. Many species are so specialized to
microhabitats within the forest that they can only be found in small
areas. Their specialization makes them vulnerable to extinction. In
addition to the species lost when an area is totally deforested, the
plants and animals in the fragments of forest that remain also become
increasingly vulnerable, sometimes even committed, to extinction. The
edges of the fragments dry out and are buffeted by hot winds; mature
rainforest trees often die standing at the margins. Cascading changes in
the types of trees, plants, and insects that can survive in the fragments
rapidly reduces biodiversity in the forest that remains. People may
disagree about whether the extinction of other species through human
action is an ethical issue, but there is little doubt about the practical
problems that extinction poses.
First, global markets consume rainforest products that depend on sustainable harvesting: latex, cork, fruit, nuts, timber, fibers, spices, natural oils and resins, and medicines. In addition, the genetic diversity of tropical forests is basically the deepest end of the planetary gene pool. Hidden in the genes of plants, animals, fungi, and bacteria that have not even been discovered yet may be cures for cancer and other diseases or the key to improving the yield and nutritional quality of foods—which the U.N. Food and Agriculture Organization says will be crucial for feeding the nearly ten billion people the Earth will likely need to support in coming decades. Finally, genetic diversity in the planetary gene pool is crucial for the resilience of all life on Earth to rare but catastrophic environmental events, such as meteor impacts or massive, sustained volcanism.
With all the lushness and productivity that exist in tropical forests, it can be surprising to learn that tropical soils are actually very thin and poor in nutrients. The underlying “parent” rock weathers rapidly in the tropics’ high temperatures and heavy rains, and over time, most of the minerals have washed from the soil. Nearly all the nutrient content of a tropical forest is in the living plants and the decomposing litter on the forest floor.
Importance of Forests
Forests and air
Forests and water
Forests and biodiversity
Forests build resilience to natural disasters
Forests and land
Forests are a key part of the climate change solution
Healthy forests, healthy people
Forests are our livelihoods/wealth
DEFORESTATION IN BRAZIL: 60-70 percent of deforestation in the Amazon results from cattle ranches while the rest mostly results from small-scale subsistence agriculture. Despite the widespread press attention, large-scale farming (i.e. soybeans) currently contributes relatively little to total deforestation in the Amazon. Most soybean cultivation takes place outside the rainforest in the neighboring cerrado grassland ecosystem and in areas that have already been cleared. Logging results in forest degradation but rarely direct deforestation. However, studies have showed a close correlation between logging and future clearing for settlement and farming
In the Brazilian state of Mato Grosso, verdant green Amazon Rainforest is broken up by broad tracts of pale green and tan deforested land. In 2005, the government of Brazil said that 48 percent of Amazon deforestation that took place in 2003 and 2004 occurred in Mato Grosso.
The transformation from forest to farm is evident in the photo-like images, taken by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite. The top image was taken on June 28, 2006, while the middle image is from June 17, 2002. The bottom map shows the difference in deforested areas over the time period, with some of the largest cleared areas marked in red. On this map, areas that were non-forested (either naturally or already deforested) in 2002 are light gray, while areas that remained forested in 2006 are darker gray.
Although some deforestation is part of the country’s plans to develop its agriculture and timber industries, other deforestation is the result of illegal logging and squatters. The Brazilian government uses MODIS images such as these to detect illegal deforestation. Because the forest is so large and is difficult to access or patrol, the satellite images can provide an initial alert that tells officials where to look for illegal logging.
These images were produced by the MODIS Rapid Response Team, which provides both the 2006 and 2002 images in a variety of resolutions, including MODIS’maximum resolution of 250 meters per pixel.
NASA images courtesy the
MODIS Rapid Response Team at Goddard Space Flight Center. Map by Robert
July 30, 2000
The state of Rondônia in western Brazil — once home to 208,000 square kilometers of forest (about 51.4 million acres), an area slightly smaller than the state of Kansas — has become one of the most deforested parts of the Amazon. In the past three decades, clearing and degradation of the state’s forests have been rapid: 4,200 square kilometers cleared by 1978; 30,000 by 1988; and 53,300 by 1998. By 2003, an estimated 67,764 square kilometers of rainforest—an area larger than the state of West Virginia—had been cleared.
August 2, 2010
By the start of this satellite time series from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite, the frontier had reached the remote northwest corner of Rondônia. Intact forest is deep green, while cleared areas are tan (bare ground) or light green (crops, pasture, or occasionally, second-growth forest). Over the span of eight years, roads and clearings pushed west-northwest from Buritis toward the Jaciparaná River. The deforested area along the road into Nova Mamoré expanded north-northeast all the way to the BR-346 highway.
Deforestation follows a fairly predictable pattern in these images. The first clearings that appear in the forest are in a fishbone pattern, arrayed along the edges of roads. Over time, the fishbones collapse into a mixture of forest remnants, cleared areas, and settlements. This pattern follows one of the most common deforestation trajectories in the Amazon. Legal and illegal roads penetrate a remote part of the forest, and small farmers migrate to the area. They claim land along the road and clear some of it for crops. Within a few years, heavy rains and erosion deplete the soil, and crop yields fall. Farmers then convert the degraded land to cattle pasture, and clear more forest for crops. Eventually the small land holders, having cleared much of their land, sell it or abandon it to large cattle holders, who consolidate the plots into large areas of pasture.
Some areas of Rondonia, Brazil, have been almost completely deforested in just 6 years. This pair of images uses a scale, or index, of vegetation to compare forest area in 2000 to 2006 at the full resolution (15 meters per pixel) of the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument. Cleared areas (tan) spread from roads cut through the forest (green), a pattern of deforestation typical in Rondonia. (Maps by Robert Simmon, based on ASTER data.)
This map shows percent forest cover in eastern Democratic Republic of the Congo. Red areas, expanding outward from the town of Mambasa, show deforestation between 1990 and 2000. (Map by Robert Simmon, based on data from the Decadal Forest Change Mapping Project.)
Rondônia is part of the Brazilian Amazon, on the border with Bolivia. It is one of the peripheral areas undergoing expansion within Amazonia, growing from about half a million inhabitants in 1980 to more than 1.5 million in 2009. Within the Brazilian Amazon, Rondônia has the highest deforestation rate. It reached more than 34 percent in 2008, a drastic increase from 1978 when less than 2 percent had been cut. The principal causes of deforestation in the Amazon as a whole — and especially in Rondônia — are population growth due to government-promoted immigration, the growth of the wood-products industry in conjunction with the expansion of the road network, and burning for management of pastureland and agricultural fields.
Credit:NASA,Mongabay,USGS, Woods Hole Research Center,UNEP