Are rainforests still worth saving?
A look at why rainforests are important
Rhett Butler, mongabay.com
April 20, 2005
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 levels 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.
Local people most affected
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 with valuable services such as erosion prevention, flood control, water treatment, 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. Finally, deforestation negates any possibility of ecotourism in the area. Ecotoursists are uninterested and unwilling to visit denuded landscapes devoid of wildlife.
- Conflicts with wildlife: As their habitat dwindles, many animals are forced to forage outside their traditional forest range and move into areas populated by humans and conflicts arise. Crop damage and death by wildlife are increasingly a problem in some areas in the tropics.
- Emergence of disease: The emergence of tropical diseases and outbreaks of new diseases including nasty hemorrhagic fevers like Ebola and Lassa Fever is a subtle but serious impact of deforestation. With increased human presence in the rainforest, and exploiters pushing into deeper areas, man is encountering "new" microorganisms with behaviors unlike those previously known. As the primary hosts of these pathogens are eliminated or reduced through forest disturbance and degradation, disease can break out among humans.
- Erosion: The loss of trees, which anchor the soil with their roots, causes widespread erosion throughout the tropics. The rate of increase for soil loss after forest clearing is astonishing; a study in Ivory Coast 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.
Is the weather changing?
Rainforests play a critical role in regional weather by contributing moisture to local humidity through transpiration -- the process by which plants release water through their leaves. It is estimated that Amazon forest creates 50-80% of its own rainfall through this process. Thus, as forest is felled, degraded, and cleared there is less heat absorption by vegetation and less moisture is evapotranspired into the atmosphere. The result: fewer rain clouds are formed and less precipitation falls on the forest -- NASA researchers confirmed this with their finding that during the Amazon dry season there was a distinct pattern of lower rainfall and warmer temperatures over deforested regions. The forest becomes drier contributing to a positive feedback loop where rainforest is replaced with savanna which transpires less and less moisture and is more susceptible to fires, which in themselves may alter regional climate by inhibiting cloud formation.
The buildup of carbon dioxide and other gases in the atmosphere is known as the "greenhouse effect." The buildup of these gases is believed to have altered the earth's radiative balance meaning more of the sun's heat is absorbed and trapped inside the earth's atmosphere, producing global warming.
Some carbon emissions can be mititgated by the planting of trees which absorb carbon into their vegetation through photosynthesis. Tropical forests have the best potential for the mitigation of greenhouse gases since have the greatest capacity to store carbon in their tissues as they grow. Reforestation of 3.9 million square miles (10 million square km) could sequester 100-150 billion metric tons of carbon dioxide over the next 50-100 years.
Tropical rainforests also are responsible for adding oxygen to the atmosphere as a by-product of photosynthesis. It is estimated that 20% of the the planet's oxygen is produced by the world's rainforests. Cutting the rainforest diminishes the capacity of the global system to supply oxygen reserves.
The last goodbye; a more crowded but lonelier planet
Perhaps the greatest loss from the continuing destruction of tropical forests is the extinction of species contribute to the planet's biodiversity. Species extinction is not a new process -- it has happened since the dawn of life -- but the nature of the current extinction wave is unlike any to have occurred before. The extinction rate of today may be 1,000 to 10,000 times the biological normal, or background extinction rate, of 1-10 species extinctions per year. This loss of species, unlike some of the other consequences of deforestation, is largely irrevesibble in our time since we probably only know of a small fraction of the species disappearing. Bioengineering and cloning is not possible if we don't know what we've lost.
Photo by Jen Caldwell
Extinction scientists and ecologists typically use some form of the species-area curve to determine rates of species loss. Essentially the species-area curve predicts that a 90 percent reduction in an area of habitat will result in the loss of 50 percent of its species.
While so far there is no evidence for the massive species extinctions predicted by the species-area curve, some leading ecologists believe that species extinction, like global warming, has a time lag, and the loss of forest species due to forest clearing in the past, may not be apparent yet today. In his The Call of Distant Mammoths Peter Ward uses the term "extinction debt" to describe such extinction of species and populations long after habitat alteration. An example can be seen in a study of West African primates that found an extinction debt of over 30% of the total primate fauna as a result of historic deforestation. This suggests that protection of remaining forests in these areas might not be enough to prevent extinctions caused by past habitat loss. While we may be able to predict the effects of the loss of some species, we know too little about the vast majority of species to make reasonable projections. The unanticipated loss of unknown species will have a magnified effect over time.
Besides losing unique species that add character to the planet and have instrinsic value of their own right, we are losing an incredible pool of genetic diversity which we could harness to help our own kind. As each species is lost, a unique combination of genes which has been produced over the course of millions of years, is lost and will not be replaced during our time. We head toward a future impoverished of the magnificent that we remember learning about as children: ferocious tigers; armored rhinos; brilliant macaws; colorful frogs and toads. As these species vanish from the globe, the world is truly a poorer place. Biodiversity will recover after humanity is gone, but in the meantime, the continuing loss of our fellow species will make Earth an awfully crowded, but lonely place.
Past extinctions have shown it takes at least 5 million years to restore biodiversity to the level equal to that prior of the extinction event event. Our actions today will determine whether Earth will be biologically impoverished for the 500 trillion or more humans that will inhabit the earth during that future period.
The extinction event that is occurring as you read these words rivals the extinctions caused by natural disasters of global ice ages, planetary collisions, atmospheric poisoning, and variations in solar radiation. The difference is that this extinction was conceived by humans and subject to human decisions. We are the last, best hope for life as we prefer it on this planet.
The value of rainforests
Considering their economic, recreational, and social value, there is little doubt that humanity is better off making its best effort to conserve the world's remaining rainforests. A lot can still be done. Using our intelligence and ingenuity, the human species can preserve biodiversity and unique places for future generations, without compromising the quality of life for present populations. Anything less reduces our options in the future and leaves the planet a poorer place.