Half Of The Earth's Plant Species example essay topic

The tropical rainforests are falling at human hands. The world's oldest living ecosystem is under threat in our conquest for farmland, timber, minerals, and other resources (Grainger 17). These forests cover 2% of the Earth's surface, or 6% of its landmass, yet they house over half the plant and animal species on Earth ("Rainforests"). Rainforests originally covered twice that area. Deforestation is occurring on such a scale that if it were to continue "at present rates the forests could disappear within the next one to two hundred years" (Grainger 17).

Why should we be concerned? Deforestation poses a threat to the rich biological diversity of tropical rainforests, hinders the advancement of medicinal discoveries, and contributes largely to the greenhouse effect. Because if the forests go, then so will many of the species that they support. This greatly reduces the biological diversity of the whole planet. Secondly, deforestation curtails "our future options to exploit other plants for medicines", (Grainger 17). Finally, it will contribute to the impending global climate change through the greenhouse effect (Grainger 18).

For these reasons it is imperative to control deforestation so that a large area of tropical rainforest will remain. Tropical rainforests are defined by two primary factors: location (in the tropics) and amount of rainfall they receive ("Rainforests"). Rainforests receive from 4 to 8 meters of rain a year ("Rainforests"). Most of the rainfall is blocked by the heavy vegetation, and water reaches the forest floor by rolling down branches and trunks. Another distinctive characteristic is that the rainforests have no "seasonality"- no dry or cold season of slower growth ("Rainforests"). In addition, they are the Earth's oldest living ecosystems.

The Rainforests are a "priceless part of our natural heritage" and their removal through deforestation would mean the loss of one of the planet's most valuable ecosystems (Grainger 146). Rainforests are being destroyed at an astounding rate. According to the National Academy of Science, at least 50 million acres a year are lost, "an area the size of England, Wales, and Scotland combined", ("Rainforests"). "All the primary rainforests in India, Bangladesh, Sri Lanka and Haiti have been destroyed already" ("Rainforests"). In addition, the rainforests of the Ivory Coast have almost been completely logged. Areas such as the Philippines and Thailand lost over 50% of their rainforests by 1985 ("Rainforests").

These statistics prove that there is no more powerful reason for wanting to preserve the tropical rainforests. Biological diversity, often shortened to "biodiversity", has three main components: ecosystem diversity, species diversity, and genetic diversity. So the biodiversity of a given area is characterized by the presence of different kinds of ecosystems; its species diversity; and its contribution to the genetic diversity of particular species (Grainger 147). According to the National Academy of Sciences, a typical four square mile patch of rainforest contains as many as 1500 species of flowering plants, 750 species of trees, 125 mammal species, 400 species of birds, 100 of reptiles, 60 of amphibians, and 150 species of butterflies ("Rainforests").

In particular, deforestation threatens to reduce these numbers of species, degrade the genetic diversity of individual species, and hinder the survival rate of species already exploited in their wild form in the forests. Major consequences arise for plant and animal species as a result of deforestation. All forms of disturbance displace animals from part or all of their territories. The more extensive the disturbance, the more likely animals in an area will become overcrowded and their populations will decline due to social pressures, limitations on food, and impaired reproductive activity (Grainger 150). Even by just removing a few plants, the complex annual calendars of food sources could be disrupted. These annual food source schedules enable many rainforest animals, like the orangutan, to cope with the "low density and irregular flowering and fruiting regimes of the plants they eat" (Grainger 150).

Moreover, other plants may be affected "if animals on which they rely for pollination or dispersal leave to search for food elsewhere" (150). Furthermore, genetic diversity of individual species is also being degraded. This is a concern to plant breeders because several of these species are commercially valuable crops (Grainger 147). Their degradation will "threaten our ability to continue breeding new varieties to keep ahead of pests and diseases that threaten products". Several key economic crops that originate in the humid tropics and still grow there today are brazil nut, cashew nut, cocoa, passion fruit, pineapple, rubber, papaya, bamboo, banana, ginger, rice and yam (Grainger 152).

Crops that grow on the outskirts of the forests have been bred from wild plants to give the best yields under particular environmental conditions. Extracts from the wild plants have been taken in order to make use of specific genetic characteristics from the entire population. "It is vital to retain a wide genetic diversity of wild plants so that plant breeders can counter threats to crop productivity caused by new pests and diseases and changing climate". For example, in the Amazon huge sums of money are spent in breeding new groundnut varieties resistant to diseases such as leaf spot (Caufield).

Also, some high yielding rice varieties last only two years before being attacked by a new insect pest and needing replacement (Grainger 152). Deforestation is increasing the rate of species extinction so that the plants we are using will disappear along with many animals also. "Extinction is an irreversible change and once a species is gone it is lost for good" (Grainger 150). It occurs naturally at a rate of about one species every two years (150). Species are put at much risk early on when their numbers drop so low that they could be eliminated by drought, disease or other random events. There are many endangered species found in the tropical rainforests that risk extinction if the present conditions continue.

Some examples are the kou pray or wild cow of Southeast Asia, of which only 100 individuals remain, the broad-nosed lemur from Madagascar, which is down to just two colonies, and the southern bearded saki, a monkey living in the forests of the northeast Amazonia (150). Many medical advances have come from the abundant botanical resources of the tropical rainforests. Half of the Earth's plant species live there and only 1% have been thoroughly examined for medicinal potentials ("Rainforests"). Extracts from organisms are used directly as drugs for many maladies ranging from headaches to lethal diseases such as malaria. An aid in the cure of malaria, quinine, is an alkaloid extracted from the bark of the cinchona tree found in Latin America and Africa ("Rainforests"). Also, the alkaloid d-turbocuarine found in the "deadly poisonous bark of curare lianas is used to treat diseases such as multiple sclerosis, Parkinson's disease, and other muscular disorders".

Lastly, two important anti-tumor agents are found in periwinkle from Madagascar. "One provides for a 99% chance of remission in cases of lymphatic leukemia. The other offers a life remission in 58% of Hodgkin's Disease sufferers". In addition, chemical structures from organisms serve as templates for which scientists can chemically synthesize drug compounds. Approximately 7,000 medical compounds prescribed by Western doctors are derived from plants that reside in the rainforests ("Rainforests"). The blueprint for aspirin is found in extracts from willow trees in the rainforest for example.

And ninety percent of prescription drugs that are based on higher plants from the rainforest include direct extractions from those plants ("Rainforests"). Finally, the plants of the rainforest provide aids for research. Some plants provide testing agents for potentially harmful food or drug products while other plant compounds allow scientists to understand how cancer cells grow ("Rainforests"). Also, tropical forests "offer hope to safer contraceptives."Approximately 4,000 plant species have been shown to offer contraceptive possibilities".

This is a notable fact since the exponential growth of the world's population is in need of more effective birth control methods. Deforestation also contributes significantly to the greenhouse effect and global warming. The greenhouse effect describes how Earth's atmosphere functions. To begin, the sun emits short wave radiation through the atmosphere to the Earth. In return, the Earth radiates some of the sun's energy back into the atmosphere in the form of long-wave infrared radiation. Certain trace gases such as carbon dioxide, methane, ozone, and nitrous oxide retain heat by trapping some of the infrared radiation.

Without these "greenhouse gases" the Earth would be 33 C cooler than it is now ("Rainforests"). Clearing and burning rainforests releases considerable amounts of greenhouse gases into the atmosphere. "Each year, deforestation contributes 23-30 percent of all carbon dioxide in the atmosphere" ("Rainforests"). Deforestation is also responsible for destroying our means of absorbing and storing the substance. This leads to global warming because the Earth has lost one of its only ways to absorb excess atmospheric carbon.

Through photosynthesis the rainforests absorb the carbon dioxide and emit oxygen. Yet, with deforestation there is "more and more carbon released into the atmosphere" due to the burning of the plants, and "less and less forests to remove the carbon from the atmosphere" ("Rainforests"). Rapid warming of the atmosphere can have tremendous consequences. First, many species will not be able to survive the climate change or may not be able to continue life in another habitat. Secondly, the sea level will rise approximately 1.5 meters which will cause coastal flooding ("Rainforests"). Also, an impact can occur on agriculture in food exporting nations such as the United States, Canada and France as a result of drought and drier soil conditions ("Rainforests").

And lastly, there will be increases in severe storms such as hurricanes, cyclones, and typhoons ("Rainforests"). Tropical deforestation has many significant environmental impacts. It threatens the biodiversity of our planet, deters medicinal discoveries plant species may offer and contributes to potential global warming resulting from the greenhouse effect. In conclusion, conservation of the tropical rainforests is imperative in order to preserve one of the Earth's oldest, most rich and valuable ecosystems

Bibliography

Caufield, C. In the Rainforest. New York: Alfred Knopf, 1984.
Grainger, Alan. Controlling Tropical Deforestation. London: Earths can Publications Ltd, 1993.
Rainforests: Lungs of the Planet" Rainforest Action Network. 24 Feb. 2003.