Главная > Реферат >Остальные работы
The Taiga Biome Essay, Research Paper
Between the tundra to the north and the deciduous forest to the south lies the vast expanse of the taiga, also known as the coniferous or boreal forest; the largest biome in the world and the second largest forest in the world, with only the great Siberian forest exceeding it in size. This cold-climate biome supports a dense belt of coniferous, or cone-bearing, trees extending all across North America, Europe and Asia at high altitudes. In North America, the taiga is located mainly in Canada and Alaska. In Europe, it lies in Sweden, Finland, Norway, and extends from Russia into Asia and down to Mongolia and China. Special adaptations by the plants and animals allow this biome to flourish despite the sub-zero temperatures in winter and wildfires in summer.
Rainfall is moderately high and spread throughout the year, and snow blankets the ground during the winter. With low temperatures normal throughout most of the year, little water is evaporated by the sun. Lakes, ponds, and bogs are highly abundant, especially in glacially carved areas where water is allowed to pool. The average temperature in the taiga is below freezing for six months of the year. The temperatures in the taiga can dip to a low of 54.C below zero (-65.F) during these months, but the average summer temperature rises to 15.C (60.F), warm enough to support the growth of trees.
Trees in this area use lots of energy to grow leaves in the spring. Some trees would not have enough energy to survive after growing their leaves. The coniferous trees have adapted by keeping their needles, which are modified leaves, year-round. That way, when the sun returns in the spring, the trees are already collecting vital sunlight instead of growing new leaves. The trees that grow there must face long periods of cold and drought, winds, and very poor soils. The soil is not only thin in depth, scraped away by the movements of glaciers, but also very acidic. This acidity comes from the pine needles themselves as they decompose on the forest floor. The trees fill their needles with chemicals to repel grazing animals such as deer and moose. The chemicals in the decomposing leaves form black humus and seep down through the layers of soil leaching valuable minerals and nutrients to below the root zone. The absence of earth churning invertebrates, like earthworms, means the soil becomes hard and compacted. The conifers do have an ally however: certain kinds of fungi live among the root hairs of the trees. The fungi are able to decompose the leaf litter and make the nutrients available to the trees, and the trees contribute carbohydrates in return.
Conifers have several adaptations that make them well suited to their northern environment. Their needles are thin and waxy protecting them from becoming dried out, and the deep green color helps them absorb the maximum warmth from the sun. Their branches are flexible and down drooping to prevent breakage by heavy snowfalls, and because they retain their needles year-round they are ready for food-production (photosynthesizing) as soon as the sunlight is adequate.
The most common evergreens in the taiga are the spruce, balsam fir, and pine. Other types include hemlock, cedar, redwood, and juniper, which can be found at varying latitudes. Just as latitude influences species, so also does altitude. In the northern Rocky Mountains the lower slopes may be dominated by ponderosa and sugar pine. At about 4,000 feet Douglas fir and white fir appear, and above 9,000 feet alpine fir and whitebark pine can be found. In the southern Rockies a most unusual pine is found, the bristlecone pine. Some of these gnarled and stunted trees are as much as 4,000 years old and they are generally found above the 10,000 foot mark, where the soil and the climate are very inhospitable to all but the toughest survivors.
Evergreens can survive in areas that are far too cold or dry for deciduous trees due to their effective conservation of moisture. However, in some places there is sufficient rainfall for deciduous growth, conifers are able to take over because of another set of adaptations that allow them to not only survive but also benefit from the occurrence of fire. Pines have a pulpy bark that does not easily burn and protects the inner layers of the tree from heat. The buds are protected by a cloak of long needles that burn, but not nearly as fast as other leaves, and with less heat-generation. Other adaptations to fire include cones that only release their seeds when dried and split open by the heat. The needles that the pines shed decay very slowly but are very flammable, so wildfire spreads over the ground quickly killing competing plants, harmful insects and fungi, and releasing the nutrients tied up in the fallen needles to the pine-tree roots.
Fire in a forest is not necessarily a bad thing. Fire has been used by nature to clear away shrubby growth, return nutrients to the soil, open clearings in dense forests to allow new growth that can provide wildlife with new food sources, and allow heat-sensitive cones and seeds to germinate. In forests that have been allowed to burn periodically the large healthy trees have little damage done to them and most wildlife is able to outrun or burrow in long enough to make it. It is when human intervention attempts to protect a forest from fire that a great deal of deadwood and low shrub material has accumulates, fueling a forest fire harmful to the ecosystem. However, even a hot devastating fire merely opens up new opportunities for a whole new set of plants and animals to move into.
The vegetative offerings in the coniferous forest are not very edible to most animals. Pine needles are eaten by very few of the forest s inhabitants with the exception of certain caterpillars and grubs. The seeds in the cones are more desirable but not easy to extract. One kind of bird, the crossbill, has a specialized beak that allows it to pry the cone open and a type of nutcracker bird has a bill that is large and powerful enough to break the cones open. There are several small mammals, like squirrels, voles, and lemmings, which feed on the pine seeds also. These mammals are the mainstay of the taiga food web. Their amazing birthrate keeps their numbers up even as they are heavily preyed upon as long as sufficient food is available to them. Predators that will feed on the small mammals include owls, wolves, fishers, weasels, and wolverines. The largest predators, grizzlies, lynx, and mountain lions, will feed on the smaller mammals as well as moose or elk when they can pick out a young or weakened individual.
Many animals migrate to the taiga seasonally, while resident animals have learned to adapt to the cold. For the species that reside in the taiga during the winter months, adaptations to conserve heat are important. Some animals have adapted by going into long-term hibernation (sleeping through the winter in a den or burrow). Other animals, such as the Canadian lynx, grow a dense insulating layer of fur or feathers. This fur is often camouflaged (usually white) to blend in with the snow for those that do not hibernate. Some taiga animals, like the Alaskan brown bear, tend to gain large body sizes (lots of fat) in winter to maintain a high core temperature , and are rounded in shape with short arms and legs to minimize heat loss from skin surfaces and long limbs.
Part of America s history is tied to the animal inhabitants of the coniferous forest. Early trappers traveled throughout this area hunting for the valuable furred animals like martens, fishers, weasels, mink, otters, and wolverines. Trappers would also take beaver, wolves, and bears. The early settlers depended on moose, elk, and bears for their hides and for the quantity of food they provided for the winter. But the biggest threat to the animals of the coniferous forest has been the increased human population and habitat reduction due to deforestation that resulted as civilizations grew and expanded northward in search of land and resources.
Ever since agriculture began around 11,000 years ago, humans have been clearing land for farms. Forest fires, industrial pollution, and paper use have demolished most of the population of trees in our world. This state of decreasing population of trees and forests is called deforestation. It is a very big problem in the taiga biome. The taiga in Russia accounts for approximately one-fifth of the world’s total forested land (more than two million square miles) and contains about one-half of the world’s evergreen forest. Since the collapse of the Soviet Union, the Russian government, desperate for investment, has invited outside timber companies to log the taiga forest. Russia has loosened its control over the timber and wood-products industries in the economy, which had been state-run monopolies under the old Soviet Union. This has raised concern among scientists and environmentalists about the impact of taiga deforestation on global warming. Russian forests are disappearing at a rate of 12 million hectares a year.
If carbon dioxide and other heat trapping gases continue to build up in the atmosphere at the present rate, the earth’s average temperature will rise by 3 to 8 degrees Fahrenheit in the next century. Since the forest continuously removes carbon gases from the atmosphere and replaces them with oxygen, preserving the taiga may be important to controlling the greenhouse effect. Destruction of the forests can and will accelerate global warming. The Weyerhaeuser Company, a large American wood products company, is contemplating a logging, processing, and replanting operation in a proposed wilderness area that contains pristine forests of spruce, fir, and lurch trees. Although opposed by many environmental groups, so far it has been one of the only logical plans to preserve the forests but also allow humans to meet their needs of paper and paper products.
Andrews, W.A. “The Coniferous Forest.” Terrestrial Ecology, p.62-69. Ontario:
Prentice-Hall Of Canada Ltd., 1974.
Biome-Taiga. Online. 1 October 2000.
Platt, Rutherford. The Great American Forest. New Jersey: Prentice-Hall, 1965.
Taiga. The Animals! 2.0. Version 2.0. CD-ROM. Mindscape, Inc., 1994. IBM-PC
Taiga Biome. Online. 25 September 2000.
Taiga Deforestation. Online. 1 October 2000.
The Taiga Biome. Online. 27 September 2000.
- The Greenhouse Effect Essay, Research Paper Introduction The Earth’s climate is the result of extremely complex ... or heat, emitted by the earth, thus keeping the earth warmer than it ... and famine.Regions of transition between biomes are very vulnerable to small ...
- Desert Biome Essay, Research Paper DESERT BIOME Any barren region that supports ... supply. Desert shrubs in the hollows between the dunes signal its presence. Desert ... usually drop off as the plant matures. The cactus thus avoids a huge loss ...
- ... Essay, Research Paper In the original Greek "oikos" means, "house". So ecology is "the ... between members of the same species and interspecific competition is between different species. The ... those of animals, not only usually identify biomes more because the ...
- ... , The Amazon Essay, Research Paper Rainforest Destruction: The Amazon “We as humans have the capability ... will affect the unique biome itself, lives of the natives, an ... killings has happened between these two. Destruction of the Rainforest Effects Habitat ...
- Temperate Deciduous Forests Essay, Research Paper A Deciduous forest is one in ... , Europe and China. These areas each have a growing season between 140- 300 days ... this, the temperate forest?s biome is one of the most altered biomes on the planet ...