domingo, 5 de octubre de 2008

The tundra biome


Tundra is the coldest of all the biomes. Tundra comes from the Finnish word tunturi, meaning treeless plain. It is noted for its frost-molded landscapes, extremely low temperatures, little precipitation, poor nutrients, and short growing seasons. Dead organic material functions as a nutrient pool. The two major nutrients are nitrogen and phosphorus. Nitrogen is created by biological fixation, and phosphorus is created by precipitation.
Characteristics of tundra include:
Extremely cold climate
Low biotic diversity
Simple vegetation structure
Limitation of drainage
Short season of growth and reproduction
Energy and nutrients in the form of dead organic material
Large population oscillations
Tundra is separated into two types:
Arctic tundra
Alpine tundra

The grassland biome


Grasslands are characterized as lands dominated by grasses rather than large shrubs or trees. In the Miocene and Pliocene Epochs, which spanned a period of about 25 million years, mountains rose in western North America and created a continental climate favorable to grasslands. Ancient forests declined and grasslands became widespread. Following the Pleistocene Ice Ages, grasslands expanded in range as hotter and drier climates prevailed worldwide. There are two main divisions of grasslands:
Tropical grasslands or savannas
Temperate grasslands

The forest biome


About 420 million years ago, during the Silurian Period, ancient plants and arthropods began to occupy the land. Over the millions of years that followed, these land colonizers developed and adapted to their new habitat. The first forests were dominated by giant horsetails, club mosses, and ferns that stood up to 40 feet tall.
Life on Earth continued to evolve, and in the late Paleozoic, gymnosperms appeared. By the Triassic Period (245-208 mya), gymnosperms dominated the Earth's forests. In the Cretaceous Period (144-65m mya), the first flowering plants (angiosperms) appeared. They evolved together with insects, birds, and mammals and radiated rapidly, dominating the landscape by the end of the Period. The landscape changed again during the Pleistocene Ice Ages — the surface of the planet that had been dominated by tropical forests for millions of years changed, and temperate forests spread in the Northern Hemisphere.
Today, forests occupy approximately one-third of Earth's land area, account for over two-thirds of the leaf area of land plants, and contain about 70% of carbon present in living things. They have been held in reverence in folklore and worshipped in ancient religions. However, forests are becoming major casualties of civilization as human populations have increased over the past several thousand years, bringing deforestation, pollution, and industrial usage problems to this important biome.
Present-day forest biomes, biological communities that are dominated by trees and other woody vegetation, can be classified according to numerous characteristics, with seasonality being the most widely used. Distinct forest types also occur within each of these broad groups.
There are three major types of forests, classed according to latitude:
Tropical
Temperate
Boreal forests (taiga)

The desert biome


Deserts cover about one fifth of the Earth's surface and occur where rainfall is less than 50 cm/year. Although most deserts, such as the Sahara of North Africa and the deserts of the southwestern U.S., Mexico, and Australia, occur at low latitudes, another kind of desert, cold deserts, occur in the basin and range area of Utah and Nevada and in parts of western Asia. Most deserts have a considerable amount of specialized vegetation, as well as specialized vertebrate and invertebrate animals. Soils often have abundant nutrients because they need only water to become very productive and have little or no organic matter. Disturbances are common in the form of occasional fires or cold weather, and sudden, infrequent, but intense rains that cause flooding.
There are relatively few large mammals in deserts because most are not capable of storing sufficient water and withstanding the heat. Deserts often provide little shelter from the sun for large animals. The dominant animals of warm deserts are nonmammalian vertebrates, such as reptiles. Mammals are usually small, like the kangaroo mice of North American deserts.
Desert biomes can be classified according to several characteristics.There are four major types of deserts:
Hot and dry
Semiarid
Coastal
Cold

The marine biome


Marine regions cover about three-fourths of the Earth's surface and include oceans, coral reefs, and estuaries. Marine algae supply much of the world's oxygen supply and take in a huge amount of atmospheric carbon dioxide. The evaporation of the seawater provides rainwater for the land.
Oceans
Coral reefs
Estuaries

The freshwater biome


Freshwater is defined as having a low salt concentration — usually less than 1%. Plants and animals in freshwater regions are adjusted to the low salt content and would not be able to survive in areas of high salt concentration (i.e., ocean). There are different types of freshwater regions:
Ponds and lakes
Streams and rivers
Wetlands


4 biomes..!!


Conservation and preservation of biomes

A coral reef surrounds an island in French Polynesia. Because we share the world with many other species of plants and animals, we must consider the consequences of our actions. Over the past several decades, increasing human activity has rapidly destroyed or polluted many ecological habitats throughout the world. It is important to preserve all types of biomes as each houses many unique forms of life. However, the continued heavy exploitation of certain biomes, such as the forest, freshwater, and marine, may have more severe implications. Forests are important as they are home to the most diverse biotic communties in the world. Hidden within these biomes are potential medicines and many thousands of unseen and undiscovered species. Also, forests have a global climate-buffering capacity, so their destruction may cause large-scale changes in global climate. Logging has depleted many old-growth temperate forests. The increased demand for homes, paper, and other wood products have not allowed for much conservation. More recently, people have begun to realize that logging has cleared much of these forests. Wiser use of the forests and efforts to replant trees have helped to slow down the depletion of these communities. Tropical forests have fallen victim to timber exploitation, slash and burn farming, and clearfelling for industrial use or cattle ranching, particularly in Latin America. Our increasing demand for meat products has spurred these events. For years, this destruction was occuring at a rapid rate. Over half of the world's original tropical forests are already gone. Public attention to this exploitation have helped to alleviate the problem somewhat, though many challenges are still to be faced. The freshwater and marine biomes are probably the most important of all the biomes. Their medium, water, is a major natural resource. Water is the basis of life, it supports life, and countless species live in it for all or part of their lives. Freshwater biomes supply us with our drinking water and water for crop irrigation. The world's oceans have an even greater effect on global climate than forests do. Water has a high capacity for heat, and because the Earth is mostly covered with water, the temperature of the atmosphere is kept fairly constant and able to support life. In addition to this climate-buffering capacity, the oceans contain several billion photosynthetic plankton which account for most of the photosynthesis occuring on Earth. Without these, there might not be enough oxygen to support such a large world population and complex animal life. Freshwater biomes have suffered mainly from pollution. Runoff containing fertilizer and other wastes and industrial dumpings enter into rivers, ponds, and lakes and tend to promote abnormally rapid algae growth. When these algae die, dead organic matter accumulates in the water. This makes the water unusable and it kills many of the organisms living in the habitat. Stricter laws have helped to slow down this thoughtless pollution. Overfishing and pollution have threatened to make oceans into ecological disaster areas. Industrial pollutants that are dumped upstream of estuaries have rendered many marine habitats unsuitable for life. Again, tighter regulations have been used to prevent further destruction of the ocean biomes. By educating people about the consequences of our actions, we can all gain a better understanding of how to preserve the Earth's natural biomes. The areas that have been destroyed the most will never regain their original forms, but conservation will help to keep them from getting worse.

BiOoomes

The world's biomes
Biomes are defined as "the world's major communities, classified according to the predominant vegetation and characterized by adaptations of organisms to that particular environment". The importance of biomes cannot be overestimated. Biomes have changed and moved many times during the history of life on Earth. More recently, human activities have drastically altered these communities. Thus, conservation and preservation of biomes should be a major concern to all. Here we group biomes into six major types:
Freshwater
Marine
Desert
Forest
Grassland
Tundra