This week we look at ground level to consider deforestation and next week the effect on the seas
Forests play a vital role in maintaining the balance of the Earth’s ecosystems. They provide habitat for more than half of all terrestrial species, help filter pollutants out of the air and water, and prevent soil erosion. Rainforests also provide essential hydrological (water-related) services. For example, they tend to result in higher dry season streamflow and river levels, since forests slow down the rate of water or rain run-off, and help it enter into the aquifer.
Without a tree cover, the water tends to run off quickly into the streams and rivers, often taking a lot of topsoil with it. Forests also help the regional climate as they cycle water to the interior of a continent. The shrinking of the Amazon Rainforest reduces regional rainfall, which in turn threatens the health of the remaining forest and of the agricultural land in Southern Brazil. This also results in an increased fire risk.
Forests and their soils also play a critical role in the global carbon cycle. The level of CO2 in the atmosphere depends on the distribution or exchange of carbon between different “carbon pools” as part of the carbon cycle. Forests and their soils are major carbon pools, as are oceans, agricultural soils, other vegetation, and wood products: the carbon stored in the woody part of trees and shrubs (known as “biomass”) and soils is about 50% more than that stored in the atmosphere.
Trees continuously exchange CO2 with the atmosphere. The release of CO2 into the air is due both to natural processes (respiration of trees at night and the decomposition of organic matter) and human processes (removal or destruction of trees). Similarly, CO2 is removed from the atmosphere by the action of photosynthesis, which results in carbon being integrated into the organic molecules used by plants, including the woody biomass of trees. Thus forests play a major role in regulating global temperatures by absorbing heat-trapping carbon dioxide from the atmosphere, and storing it in the form of wood and vegetation – a process referred to as “carbon sequestration”.
Unfortunately, the global benefits provided by trees are being threatened by deforestation and forest degradation. ‘Deforestation’ as a shorthand for tree loss. Forest ‘degradation’ happens when the forest gets degraded, for example due to unsustainable logging practices which remove the most valuable species, or artesanal charcoal production in which only a few trees are harvested. The Earth loses more than 18 million acres of forestland every year—an area larger than Ireland—according to the United Nations Environment Programme (UNEP).
Deforestation is a major cause of global warming. When trees are burned, their stored carbon is released back into the atmosphere. As a result, tropical deforestation (including forest degradation) is responsible for about 12-15 percent of total annual global warming emissions according to estimates released for the climate change meeting in Copenhagen.
The reasons for deforestation are complex – they are a mixture of interacting and interdependent social, economic, political, demographic (or population) and governance factors. The most important factors are clearance for agriculture (including cattle ranching), poor governance (illegal logging, corruption, and ineffective law and order), insecurity of land tenure, the system of international trade, poor planning (e.g.building of major trunk roads in forest areas), and unsustainable logging.
“The tropical deforestation in Asia is driven primarily by the fast-growing demand for timber. In Latin America, by contrast, the growing demand for soybeans and beef is deforesting the Amazon. In Africa, it is mostly the gathering of fuelwood and the clearing of new land for agriculture as existing cropland is degraded and abandoned. Two countries, Indonesia and Brazil, account for more than half of all deforestation.”
Agricultural clearance is overall the most important cause of deforestation – it is estimated to be responsible for up to three quarters of deforestation and degradation. While some of this is for commercial biofuel crops like oil palm and soybean, which grow very well in tropical forest areas, much of it is also due to the basic problem of how to feed a burgeoning world population. Also many of the ‘agents of deforestation’ are among the poorest people in the world, often without land, who are forced to clear forest areas to feed their families.
At the same time, forests that have so far escaped deforestation are now threatened by climate change: In many regions of the world, more trees will die because of increasing insect infestations and forest fires. (More insects are surviving milder winters.) “Wildfires have been on the rise worldwide for half a century. Every decade since the 1950s has seen an increase in major wildfires in the United States and around the world.”
In addition to the environmental devastation, forest fires directly affect the lives of people. In the 2007 wildfires in Southern California, 900,000 people were displaced. “The total area affected by forest fires in the western US has increased by more than a factor of six in the past two decades.” Tropical rainforests, rich in biodiversity, are suffering from warmer temperatures and less rainfall, both caused by climate change. In the past, rainforests were a sink for CO2. Now with hotter temperatures, their growth is impeded, and some are actually emitting CO2.
If climate change is not mitigated, rainforests will not be able to survive. Much of the Amazon rainforest could be transformed into savannah.