Friday, 15 August 2014

World Biome

Study of World Biome


The planet Earth
Biomes are climatically and geographically defined as similar climatic conditions on the Earth, such as communities of plants, animals, and soil organisms, and are often referred to as ecosystems. Some parts of the earth have more or less the same kind of abiotic and biotic factors spread over a large area creating a typical ecosystem over that area. Such major ecosystems are termed as biomes. Biomes are defined by factors such as plant structures (such as trees, shrubs, and grasses), leaf types (such as broadleaf and needleleaf), plant spacing (forest, woodland, savanna), and climate. Unlike ecozones, biomes are not defined by genetic, taxonomic, or historical similarities. Biomes are often identified with particular patterns of ecological succession and climax vegetation (quasi-equilibrium state of the local ecosystem). An ecosystem has many biotopes and a biome is a major habitat type. A major habitat type, however, is a compromise, as it has an intrinsic inhomogeneity.
The biodiversity characteristic of each extinction, especially the diversity of fauna and subdominant plant forms, is a function of abiotic factors and the biomass productivity of the dominant vegetation. In terrestrial biomes, species diversity tends to correlate positively with net primary productivity, moisture availability, and temperature.

Ecoregions are grouped into both biomes and ecozones.
A fundamental classification of biomes is:
  1. Terrestrial (land) biomes
  2. Aquatic biomes (including Freshwater biomes and Marine biomes)
Biomes are often known in English by local names. For example, a temperate grassland or shrubland biome is known commonly as steppe in central Asia, prairie in North America, and pampas in South America. Tropical grasslands are known as savanna in Australia, whereas in Southern Africa it is known as certain kinds of veld (from Afrikaans).
Sometimes an entire biome may be targeted for protection, especially under an individual nation's Biodiversity Action Plan.
Climate is a major factor determining the distribution of terrestrial biomes. Among the important climatic factors are:
  • latitude: Arctic, boreal, temperate, subtropical, tropical.
  • humidity: humid, semi-humid, semi-arid, and arid.
    • seasonal variation: Rainfall may be distributed evenly throughout the year or be marked by seasonal variations.
    • dry summer, wet winter: Most regions of the earth receive most of their rainfall during the summer months; Mediterranean climate regions receive their rainfall during the winter months.
  • elevation: Increasing elevation causes a distribution of habitat types similar to that of increasing latitude.
The most widely used systems of classifying biomes correspond to latitude (or temperature zoning) and humidity. Biodiversity generally increases away from the poles towards the equator and increases with humidity.

  •  

Biome Classification Schemes

Biome classification schemes seek to define biomes using climatic measurements. Particularly in the 1970s and 1980s there was a significant push to understand the relationships between these measurements and properties of ecosystem energetics because such discoveries would enable the prediction of rates of energy capture and transfer among components within ecosystems. Such a study was conducted by Sims et al. (1978) on North American grasslands. The study found a positive logistic correlation between evapotranspiration in mm/yr and above ground net primary production in g/m^2/yr. More general results from the study were that precipitation and water use lead to aboveground primary production, solar radiation and temperature lead to belowground primary production (roots), and temperature and water lead to cool and warm season growth habit.[3] These findings help explain the categories used in Holdridge’sbioclassification scheme, which were then later simplified in Whittaker’s. The number of classification schemes and the variety of determinants used in those schemes, however, should be taken as a strong indicator that biomes do not all fit perfectly into the classification schemes created.

Holdridge Scheme

The Holdridge classification scheme was developed by L. R. Holdridge, a botanist. It maps climates based on four categories:
  • Average total precipitation (cm) on a logarithmic scale
  • Potential evapotranspiration ratio: the potential evapotranspiration divided by the precipitation; the ratio increases from humid to arid regions.
  • Potential evapotranspiration
  • Mean annual biotemperature (°C): calculated from monthly mean temperatures after converting any mean temperature to 0°C, based on the assumption that temperatures at or below freezing all have the same effect on plants, and delineating between -10°C and -30°C would yield unrealistic results.
In this scheme, climates are classified based on the biological effects of temperature and rainfall on vegetation under the assumption that these two abiotic factors are the largest determinants of the type of vegetation found in an area. Holdridge uses the 4 axis to define 30 so called "humidity provinces," which are clearly visible in the Holdridge diagram. While the scheme largely ignores soil and sun exposure, Holdridge did acknowledge that these, too, were important factors in biome determination.

Whittaker's Biome-type Classification Scheme

Whittaker appreciated biome-types as a representation of the great diversity of the living world, and saw the need to establish a simple way to classify these biome-types. Whittaker based his classification scheme on two abiotic factors: Precipitation and Temperature. His scheme can be seen as a simplification of Holdridge's, one more readily accessible, but perhaps missing the greater specificity that Holdrige's provides.
Whittaker based his representation of global biomes on both previous theoretical assertions as well as an ever increasing empirical sampling of global ecosystems. Whittaker was in a unique position to make such a holistic assertion as he had previously compiled a review of biome classification.
The Whittaker Classification Scheme can be viewed at the following address:

Key definitions for understanding Whittaker's Scheme

  • physiognomy: The apparent characteristics, outward features, or appearance of ecological communities or species.
  • biome: a grouping of terrestrial ecosystems on a given continent that are similar in vegetation structure, physiognomy, features of the environment and characteristics of their animal communities
  • formation: a major kind of community of plants on a given continent
  • biome-type: grouping of convergent biomes or formations of different continents; defined by physiognomy
  • formation-type: grouping of convergent formations
Whittaker's distinction between biome and formation can be simplified: formation is used when applied to plant communities only, while biome is used when concerned with both plants and animals. Whittaker's convention of biome-type or formation-type is simply a broader method to categorize similar communities. The world biome-types, as displayed on a world map, can be viewed at the following link:

Whittaker's parameters for classifying biome-types

Whittaker, seeing the need for a simpler way to express the relationship of community structure to the environment, used what he called “gradient analysis” of ecocline patterns to relate communities to climate on a worldwide scale. Whittaker considered four main ecoclines in the terrestrial realm.
Intertidal levels: The wetness gradient of areas that are exposed to alternating water and dryness with intensities that vary by location from high to low tide
  1. climatic moisture gradient
  2. temperature gradient by altitude
  3. temperature gradient by latitude
Along these gradients, Whittaker noted several trends that allow him to qualitatively establish biome-types.
  • The gradient runs from favorable to extreme with corresponding changes in productivity.
  • Changes in physiognomic complexity vary with the favorability of the environment (decreasing community structure and reduction of stratal differentiation as the environment becomes less favorable).
  • Trends in diversity of structure follow trends in species diversity; alpha and beta species diversities decrease from favorable to extreme environments.
  • Each growth-form (i.e. grasses, shrubs, etc.) has its characteristic place of maximum importance along the ecoclines.
  • The same growth forms may be dominant in similar environments in widely different parts of the world.
Whittaker summed the effects of gradients (3) and (4), to get an overall temperature gradient and combined this with gradient (2), the moisture gradient, to express the above conclusions in what is known as the Whittaker Classification Scheme. The scheme graphs average annual precipitation (x-axis) versus average annual temperature (y-axis) to classify biome-types.

Walter System

The Heinrich Walter classification scheme was developed by Heinrich Walter, a German ecologist. It differs from both the Whittaker and Holdridge schemes because it takes into account the seasonality of temperature and precipitation. The system, also based on precipitation and temperature, finds 9 major biomes, with the important climate traits and vegetation types summarized in the accompanying table. The boundaries of each biome correlate to the conditions of moisture and cold stress that are strong determinants of plant form, and therefore the vegetation that defines the region. Extreme conditions, such as flooding in a swamp, can create different kinds of communities within the same biome.
  • I: Equatorial
    • Always moist and lacking temperature seasonality
    • Evergreen tropical rain forest
  • II: Tropical
    • Summer rainy season and cooler “winter” dry season
    • Seasonal forest, scrub, or savanna
  • III: Subtropical
    • Highly seasonal, arid climate
    • Desert vegetation with considerable exposed surface
  • IV: Mediterranean
    • Winter rainy season and summer drought
    • Sclerophyllous (drought-adapted), frost-sensitive shrublands and woodlands
  • V: Warm temperate
    • Occasional frost, often with summer rainfall maximum
    • Temperate evergreen forest, somewhat frost-sensitive
  • VI: Nemoral
    • Moderate climate with winter freezing
    • Frost-resistant, deciduous, temperate forest
  • VII: Continental
    • Arid, with warm or hot summers and cold winters
    • Grasslands and temperate deserts
  • VIII: Boreal
    • Cold temperate with cool summers and long winters
    • Evergreen, frost-hardy needle-leaved forest (taiga)
  • IX: Polar
    • Very short, cool summers and long, very cold winters
    • Low, evergreen vegetation, without trees, growing over permanently frozen soils

Bailey System

Robert G. Bailey almost developed a biogeographical classification system for the United States in a map published in 1976. Bailey subsequently expanded the system to include the rest of South America in 1981 and the world in 1989. The Bailey system is based on climate and is divided into seven domains (Polar, Humid Temperate, Dry, Human, and Humid Tropical), with further divisions based on other climate characteristics (subarctic, warm temperate, hot temperate, and subtropical; marine and continental; lowland and mountain).[7]
  • 100 Polar Domain
    • 120 Tundra Division
    • M120 Tundra Division - Mountain Provinces
    • 130 Subarctic Division
    • M130 Subarctic Division - Mountain Provinces
  • 200 Humid Temperate Domain
    • 210 Warm Continental Division
    • M210 Warm Continental Division - Mountain Provinces
    • 220 Hot Continental Division
    • M220 Hot Continental Division - Mountain Provinces
    • 230 Subtropical Division
    • M230 Subtropical Division - Mountain Provinces
    • 240 Marine Division
    • M240 Marine Division - Mountain Provinces
    • 250 Prairie Division
    • 260 Mediterranean Division
    • M260 Mediterranean Division - Mountain Provinces
  • 300 Dry Domain
    • 310 Tropical/Subtropical Steppe Division
    • M310 Tropical/Subtropical Steppe Division - Mountain Provinces

WWF system

A team of biologists convened by the World Wide Fund for Nature (WWF) developed an ecological land classification system that identified fourteen biomes,[8] called major habitat types, and further divided the world's land area into 867 terrestrial ecoregions. Each terrestrial Ecoregion has a specific EcoID, fomatXXnnNN (XX is the Ecozone, nn is the Biome number, NN is the individual number). This classification is used to define the Global 200 list of ecoregions identified by the WWF as priorities for conservation. The WWF major habitat types are:

Freshwater biomes

According to the World Wildlife Fund, the following are classified as freshwater biomes:[9]

Realms or Ecozones (terrestrial and freshwater, WWF)

Marine biomes

Marine biomes (H) (major habitat types), Global 200 (WWF)
Biomes of the coastal &continental shelf areas (Neritic zone - List of ecoregions (WWF))
Realms or Ecozones (marine, WWF)
  • North Temperate Atlantic
  • Eastern Tropical Atlantic
  • Western Tropical Atlantic
  • South Temperate Atlantic
  • North Temperate Indo-Pacific
  • Central Indo-Pacific
  • Eastern Indo-Pacific
  • Western Indo-Pacific
  • South Temperate Indo-Pacific
  • Southern Ocean
  • Antarctic
  • Arctic
  • Mediterranean
Other marine habitat types
Major Habitats, Non Global 200 (WWF)

Summary - Ecological taxonomy (WWF)

Example

Anthropogenic biomes

Humans have fundamentally altered global patterns of biodiversity and ecosystem processes. As a result, vegetation forms predicted by conventional biome systems are rarely observed across most of Earth's land surface. Anthropogenic biomes provide an alternative view of the terrestrial biosphere based on global patterns of sustained direct human interaction with ecosystems, including agriculture, human settlements, urbanization, forestry and other uses of land. Anthropogenic biomes offer a new way forward in ecology and conservation by recognizing the irreversible coupling of human and ecological systems at global scales and moving us toward an understanding how best to live in and manage our biosphere and the anthropogenic biosphere we live in. The main biomes in the world are freshwater, marine, coniferous, deciduous, ice, mountains, boreal, grasslands, tundra, and rainforests.

Major Anthropogenic Biomes

  • Dense Settlements
  • Villages
  • Croplands
  • Rangelands
  • Forested

Other biomes

The Endolithic biome, consisting entirely of microscopic life in rock pores and cracks, kilometers beneath the surface, has only recently been discovered and does not fit well into most classification schemes.

 

 

 

 

 

Map of Biomes

Description: magnify-clipDescription: 800px-Vegetation-no-legend

Freshwater Biomes

Description: Major continental divides, showing drainage into the major oceans and seas of the world. Grey areas are endorheic basins that do not drain to the ocean.
Drainage basins of the principal oceans and seas of the world. Grey areas are endorheic basins that do not drain to the ocean.
[hide]v·d·eBiomes and Ecozones


Terrestrial
biomes
Polar/montane
Tundra ·Taiga, Boreal forests ·Montane grasslands and shrublands


Temperate
Coniferous forests ·Broadleaf and mixed forests ·Grasslands, savannas, and shrublands


(Sub)tropical
Coniferous forests ·Moist broadleaf forests ·Dry broadleaf forests ·Grasslands, savannas, and shrublands


Dry
Mediterranean forests, woodlands, and scrub ·Deserts and xeric shrublands


Wet
Flooded grasslands and savannas ·Riparian ·Wetland


Aquatic
biomes
Pond ·Littoral ·Intertidal zone ·Mangrove forest ·Kelp forest ·Coral reef ·Neritic zone ·Continental shelf ·Pelagic zone ·Benthic zone ·Hydrothermal vents ·Cold seeps


Other biomes
Endolithic zone


Ecozones
Afrotropic ·Antarctic ·Australasia ·Indomalaya ·Nearctic ·Neotropic ·Oceania ·Palearctic



Terrestrial biome

Introduction

Description: Figure 1: Global distribution of the Earth's thirteen major terrestrial biomes. (Original Data Source for Map: Olson, D.M. et al. 2001. Terrestrial Ecoregions of the World: A New Map of Life on Earth. BioScience 51(11): 933-938).

Figure 1: Global distribution of the Earth's thirteen major terrestrial biomes. (Original Data Source for Map: Olson, D.M. et al. 2001. Terrestrial Ecoregions of the World: A New Map of Life on Earth. BioScience 51(11): 933-938).
Many places on Earth share similar climatic conditions despite being found in geographically different areas. As a result of natural selection, comparable ecosystems have developed in these separated areas. Scientists call these major ecosystem types biomes. The geographical distribution (and productivity) of the various biomes is controlled primarily by the climatic variables precipitation and temperature. The maps in Figures 1 and 2 describe the geographical locations of the thirteen major terrestrial biomes of the world. Because of their scale, these maps ignore the many community variations that are present within each biome category.
Description: Figure 2: Distribution of the Earth's thirteen major terrestrial biomes over North and Central America. (Original Data Source for Map: Olson, D.M. et al. 2001. Terrestrial Ecoregions of the World: A New Map of Life on Earth. BioScience 51(11): 933-938).

Figure 2: Distribution of the Earth's thirteen major terrestrial biomes over North and Central America. (Original Data Source for Map: Olson, D.M. et al. 2001. Terrestrial Ecoregions of the World: A New Map of Life on Earth. BioScience 51(11): 933-938).
Most of the classified biomes are identified by the dominant plants found in their communities. For example, the various types of grasslands are dominated by a variety of annual and perennial species of grass, while deserts are occupied by plant species that require very little water for survival or by plants that have specific adaptations to conserve or acquire water.
The diversity of animal life and subdominant plant forms characteristic of each biome is generally controlled by abiotic environmental conditions and the productivity of the dominant vegetation. In general, species diversity becomes higher with increases in net primary productivity, moisture availability, and temperature.
Adaptation and niche specialization are nicely demonstrated in the biome concept. Organisms that fill similar niches in geographically separated but similar ecosystems usually are different species that have undergone similar adaptation independently, in response to similar environmental pressures. The vegetation of California, Chile, South Africa, South Australia, Southern Italy and Greece display similar morphological and physiological characteristics because of convergent evolution. In these areas, the vegetation consists of drought-resistant, hard-leaved, low growing woody shrubs and trees like eucalyptus, olive, juniper, and mimosa.

 

Tundra

The geographical distribution of the tundra biome is roughly poleward of 65° North latitude. In the Southern Hemisphere, the tundra biome has a very limited distribution. Within the tundra biome, temperature, precipitation, and evaporation all tend to be at a minimum. In fact, the tundra is the coldest of all biomes and this environmental factor has played an important role in the evolution of adaptations for plant and animal survival. Most tundra locations, have summer months with an average temperature between 3 and 12° C (37 to 54° F). The average winter monthly temperature is around -34° C (-30° F). Precipitation in the wettest month is usually no greater than 2.5 centimeters (roughly 1 inch). Yet, despite the low levels of precipitation the ground surface of the tundra biome is often waterlogged because of low rates of evapotranspiration and poor drainage.
The tundra biome is characterized by the absence of trees and the presence of low-lying shrubs, mosses, and lichens. Lack of height allows the vegetation to be protected by the insolating properties of snow during the winter season. Perhaps the most characteristic arctic tundra plants are lichens like reindeer moss (Cladonia spp.). In the drier parts of the tundra, grasses are common (Figure 3). Sedges dominate sites that have more moisture. About 400 varieties of flowering plants occur in this biome. Total species diversity of plants in the tundra biome is relatively small numbering about 2000 species. Plants are generally small, are adapted to soil disturbance, and reproduce via budding or other forms of asexual reproduction rather than sexual means. Soils of this biome are usually permanently frozen (permafrost) starting at a depth of a few centimeters to meter or more. The permafrost line is a physical barrier to plant root growth. Thus, there are no deep rooting systems. The presence of permafrost also causes poor drainage and soils are often waterlogged and chemically reduced.
Figure 3: Tundra dominated by flowering arctic cotton grass, Northwest Territories, Canada. (Image Source).
The principal herbivores of the tundra biome include caribou, musk ox, arctic hare, voles, squirrels, and lemmings (Figure 4). Most of the bird species of the tundra have the ability to migrate and live in warmer locations during the cold winter months. The herbivore species support a small number of carnivore species like the arctic fox, snow owl, polar bear, and wolves. Reptiles and amphibians are few or completely absent because of the extremely cold temperatures.
Alpine tundra is quite comparable to arctic tundra but differs in the absence of permafrost, the presence of better drainage, and more extreme annual fluctuations of air temperature. Plants species in the alpine tundra are for the most part similar to the ones found on the arctic tundra. In contrast, alpine tundra animal species tend to be quit different from those individuals that live in the arctic tundra. This takes place because alpine tundra tends to adopt migrating species during the summer months from habitats located at lower elevations.

Boreal Forests/Taiga

This moist-cool, transcontinental boreal forests or taiga biome lies largely between 50 and 65° North latitude. The climate of this biome is cool to cold with more precipitation than the tundra. Precipitation here mainly occurs in the summer because this is the season when mid-latitude cyclones move in from the south. The growth season is limited to about 130 days.
The predominant vegetation of boreal forest biome is cone bearing needle-leaf evergreen variety tree species. Four tree genera are dominant in this biome: spruce (Picea), pine (Pinus), fir (Abies), and larch (Larix). In North America, some common species include: black spruce (Piceamariana), white spruce (Piceaglauca), jack pine (Pinusbanksiana), tamarack (Larixlaricina), and balsam fir (Abiesbalsamea); with red pine (Pinusresinosa), white pine (Pinusstrobus), and hemlock (Tsugacanadensis) limited to an area north and east of the Great Lakes Region. Broad-leaf species, like alder (Alnus), birch (Betula), and aspen (Populus), are common in all areas as an early successional species after disturbance.
Understory vegetation is relatively limited as a result of the low light penetration even during the spring and fall months. Common understory species include orchids, shrubs like rose, blueberry, and cranberry. Mammals common to the boreal forest include moose, bear, deer, wolverine, marten, lynx, wolf, snowshoe hare, vole, chipmunks, shrews, and bats. Reptiles are extremely rare, once again, because of cold temperatures.  
Deep litter layers are a common characteristic of boreal forest soils. These deep litter layers accumulate because of slow decomposition rates. Soils of this biome are also acidic and mineral deficient. Mineral deficiency occurs because large amounts of water move down though the profile causing leaching.
Boreal forest soils are characterized by a deep litter layer and slow decomposition. Soils of this biome are also acidic and mineral deficient because of the large movement of water vertically though the profile and subsequent leaching.

Temperate Coniferous Forests

In North America we can find two broad areas of temperate coniferous forests in the more temperate mid-latitudes. In these areas, average annual temperatures range from 20° to 5° C (68° to 41° F). Along the west side of North America and below the boreal forest is one such area. On the wetter sites (up to 400 centimeters or 160 inches annually) that have close proximity to the Pacific Ocean are stands of very tall and productive Douglas fir (Pseudotsugamenziesii), red cedar (Thujaplicata), sitka spruce (Piceasitchensis), and redwood (Sequoia sempervirens). Some of these trees can grow to over 120 meters (390 feet) in height. Beneath the canopy of these trees is a shrub layer that includes various types of berries (Vacciniumspp.), a few herbs, and various ferns. Further inland of this temperate “rain forest” zone precipitation declines significantly, winter temperatures become colder, and summer temperatures become much warmer. This change in climate makes more drought resistant trees like ponderosa pine (Pinuspondersoa), Engelmann spruce (Piceaengelmannii), and lodgepole pine (Pinuscontorta) dominant.
Another region of temperature coniferous forests occurs in southeastern United States. The species composition of this forest ecosystem does not resemble the coniferous forests found in western North America. Instead, these forests are dominated by pitch pine (Pinusrigida), longleaf pine (Pinuspalustris), and slash pine (Pinuselliotti). All of these tree species are adapted to growing on nutrient poor sandy soils and can withstand the effects of fire. Biomass productivity is typically low in this type of temperate coniferous forest.
Outside of North America, the various types of temperate coniferous forest can also be found in northern Japan, and parts of Europe and Asia. In these areas, the plant species are similar in form and ecological function to North American species but not closely related.

Temperate Broadleaf and Mixed Forests

The temperature broadleaf and mixed forests biome (also called temperate deciduous forest) is characterized by a moderate temperate climate and a dominance of broadleaf deciduous trees. This biome once occupied much of the eastern half of the United States, central Europe, Korea, and China. Over the last few centuries, this biome has been very extensively affected by human activity. Much of it has been converted into agricultural fields or urban land-use.
Tree species diversity is this biome is moderate with 5 to 25 dominant trees at a site. Dominant trees include maple (Acer spp.), beech (Fagus spp.), oak (Quercusspp.), hickory (Caryaspp.), basswood (Tilia spp.), magnolia (Magnolia spp.), cottonwood (Populus spp.), elm (Ulmus spp.), and willow (Salix spp.). The understory of shrubs, herbs, and ferns in a mature forest are typically well developed and richly diversified. Understory plants in this biome often take advantage of the leafless condition of trees during spring and fall to concentrate their growth.
Many different types of herbivores and carnivores live in the temperate broadleaf and mixed forest. Common fauna include squirrels, rabbits, skunks, birds, deer, mountain lion, bobcat, timber wolf, fox, and bears. Some reptiles and amphibians also exist here.
Nutrient rich brown forest soils characterize the temperate broadleaf and mixed forests biome. Tree cover promotes the accumulation of organic materials in a well-developed humus layer. Surface litter layer in these soils tends to be thin because of rapid decomposition.

 

Temperate Grasslands, Savannas and Shrublands

In central North America is the temperate grasslands, savannas and shrublands biome (also called prairie). The grassland biome is also found in the continental interior of Eurasia, Australia, and South America. Prior to the arrival of settlers in North America, much of this biome was dominated by species of tall grass known as bluestem (Andropogon spp.). This particular species covered much of the eastern side of this biome forming dense covers 1.5 to 2.0 meters (4 to 6 feet) tall. In the western end of the biome, where precipitation is lower, buffalo grass (Buchloedactyloides) and other grasses only a few inches above the soil surface are common. Flowering herbs, including many kinds of composites and legumes, are common but much less important than grass species. Trees are found scattered in moist low-lying areas and along a narrow zone adjacent to streams.
Climatically, the temperate grasslands, savannas and shrublands biome can be described as being temperate. Summers are hot to warm and winters are cool to cold. Annual precipitation is less than what is received by the adjacent temperate broadleaf and mixed forests biome. Seasonally, precipitation varies from being concentrated during a few months to spread evenly through the year. This biome generally does not receive enough precipitation to support tree growth. In the wetter parts of this biome nutrient rich black chernozemic soils are common. In many parts of the world, these extremely fertile soils now support crop growth. In drier parts of prairies, soils can be influenced by salinization.
Grassland mammals are dominated by smaller burrowing herbivores (prairie dogs, jack rabbits, ground squirrels, and gophers) and larger running herbivores such as bison, pronghorn antelope, and elk. Carnivores include badger, coyote, ferret, wolf, and cougar. The populations of many of these organisms have been drastically reduced because of the conversion of their natural habitat into cropland. Some of these species are on the edge of extinction.

 

Montane Grasslands and Shrublands

The montane grasslands and shrublands biome is found at high elevations in temperate, subtropical, and tropical climates. This biome is dominated by grass and shrub species and tends to have a high number of endemic plants and animals. Examples of this biome can be found at the Tibetan plateau, Central Range in New Guinea, eastern Andes Mountains in South America, southeastern Africa, and tropical East Africa. A unique feature of many tropical examples of this biome is the presence of giant rosette vegetation belonging to the plant families Lobelia (Africa), Puya (South America), Cyathea (New Guinea), and Argyroxiphium (Hawaii) (Figure 7k-16). All of these plants have unique adaptations that allow them to successfully grow at high elevations.

Deserts and Xeric Shrublands

In its most typical form, the xeric shrublands and desert biome consists of shrub-covered land where the plants are spatially quite dispersed. This biome is geographically found from 25 - 35° North and South latitude, primarily in the interiors of continents. The formation of precipitation in desert and xeric shrublands biome is limited by the subtropical high-pressure system. Many desert areas have less than 3 centimeters (about 1 inch) of precipitation during an average year.
Dominant plants include drought resistant shrubs like the creosote bush (Larreadivaricata) and sagebrush (Artemisia tridentata), water storing succulents like cactus, and many species of short lived annuals that complete their life cycles during infrequent and short rainy periods (Figure 7k-18). Lastly, desert habitats can be completely devoid of vegetation if precipitation is in very short supply. Most desert mammals tend to be nocturnal to avoid the high temperatures. Desert habitats have a rich lizard and snake fauna because high temperatures promote the success of cold-blooded life forms. Because biomass productivity is low, the litter layer is almost nonexistent and organic content of surface soil layers is very low. Finally, evaporation tends to concentrate salts at the soil surface.

 

 

Mediterranean Forests, Woodlands and Scrub

The Mediterranean forests, woodlands and scrub biome (also called chaparral) has a very specific spatial distribution. It is found in a narrow zone between 32 and 40° latitude North and South on the west coasts of the continents. This area has a dry climate because of the dominance of the subtropical high pressure zone during the fall, summer, and spring months. Precipitation falls mainly in the winter months because of the seasonal movement of the polar front and associated mid-latitude cyclones. Precipitation varies from about 30 to 75 centimeters (12 to 30 inches) annually and most of this rain falls in a period only 2 to 4 months long.
Despite the fact that this biome is very limited geographically, it contains a high diversity of animal and plant species that are adapted to the stressful conditions of long, hot summers with little rain. The vegetation of this biome consists of many different types of annuals and drought-resistant, evergreen, short woody shrubs and trees. Dominant tree species include olive (Oleaeuropaea), eucalyptus (Eucalyptus spp.), arbutus (Arbutus unedo), acacia (Acacia spp.), maritime pine (Pinuspinaster), and various species of oak (Quercus spp.). As a result of the climate, the vegetation of this biome exhibits a number of adaptations to withstand drought and fire. Plants tend not to drop their leaves during the dry season because of the expense of replacement. The dry climate slows the rate of leaf decomposition and soils tend to be poorly developed.

 

Tropical and Subtropical Grasslands, Savannas and Shrublands

Vegetation in the tropical and subtropical grasslands, savannas and shrublands biome (also called savanna) consists of a cover of perennial grass species 1 to 2 meters (3 to 6 feet) tall with scattered drought-resistant trees that generally do not exceed 10 meters (32 feet) in height. The savanna biome constitutes extensive areas in eastern Africa, South America, and Australia. Distinct wet and dry seasons and temperatures that are hot all year long characterize the climate of this biome. Annual rainfall varies between 90-150 centimeters (35 to 60 inches).
Tree and shrub species in the savanna usually drop their leaves during the dry season. This adaptation reduces water loss from the plants during the dry winter season. Diversity of plant and animal species tends to be high. Grazing on the grasses and trees are vast herds of hoofed mammals including buffalo, giraffes, eland, impalas, oryx, gazelles, gerenuk, wildebeest, zebra, rhinoceroses, elephants, and warthogs. These herbivores supply food for carnivores like lions, cheetahs, leopards, jackals, and hyenas.

 

 

Flooded Grasslands and Savannas

In the tropical and subtropical regions of our planet are large expanses of flooded grasslands and savannas. This biome is slightly different from the savanna biome just described. Because of common flooding, these areas support additional plant and animal species adapted to thrive under this condition. For instance, this biome is home to large numbers of migratory and resident water birds.
Some examples of flooded grasslands and savannas include in the Everglades in Florida, the Sahelian flooded savannas, and the Zambezian flooded savannas. Similar to other tropical biomes, this biome has high species diversity. For example, the Everglades are home to some 11,000 species of seed-bearing plants, 25 species of orchids, 300 bird species, and 150 species of fish.

Tropical and Subtropical Moist Broadleaf Forests

The tropical and subtropical moist broadleaf forests biome (also called moist tropical rain forest) occurs in a zone about 10° of latitude either side of the equator. Annual rainfall generally exceeds 250 centimeters (100 inches) and is evenly distributed throughout the year. Temperature and humidity are relatively high through the year. Flora is highly diverse: a typical hectare (2.5 acres) may contain as many as 300 different tree species as compared to 20 to 30 in the temperate zone. The various trees of the moist tropical rain forests are closely spaced together and form a thick continuous canopy some 25 to 35 meters (80 to 115 feet) tall. Every so often this canopy is interrupted by the presence of very tall emergent trees (up to 40 meters or 130 feet) that have wide buttressed bases for support. Epiphytic orchids and bromeliads, as well as vines (lianas), are very characteristic of the moist tropical rain forest biome. Some other common plant species include ferns and palms. Most plants are evergreen with large, dark green, leathery leaves.
The ground surface of the moist tropical rain forest tends to be dark with only about 1% of the light intensity found above the forest canopy. These light poor conditions cause the understory to be sparsely vegetated. The few plants that grow at ground level do so by being able to tolerate low light levels. The moist tropical rain forest is also home to a great variety of animals. Some scientists believe that 30 to 50% of all of the Earth's animal species may be found in this biome. Most of these organisms are insects.
Decomposition is rapid in the tropical rain forest because of high temperatures and abundant moisture. Because of the frequent and intense rains, tropical soils are subject to extreme chemical weathering and leaching. These environmental conditions make tropical soils acidic and nutrient poor.

Tropical and Subtropical Dry Broadleaf Forests

Tropical and subtropical dry forests (also called seasonal tropical forest or tropical dry forest) are found in southern Mexico, southeastern Africa, central India, Indochina, Madagascar, New Caledonia, eastern Bolivia, central Brazil, the Caribbean, and along the coasts of Peru and Ecuador.This biome exists as a zone that borders the tropical and subtropical moist broadleaf forests biome. Because of its geographical location, the tropical and subtropical dry forest experiences a dry season that lasts several months. This abiotic condition has a great effect on living things in this biome. Many of these species that live here have specific adaptations to help them survive the dry period. Consequently, deciduous trees like teak, mahogany, and mountain ebony dominate these forests. During the seasonal drought these trees loose their leaves to conserve water.The leafless condition also causes more sunlight to reach ground surface and this condition facilitates the growth of thick shrub layer. While less diverse than tropical rain forests, seasonal tropical forests still have a vast assortment of organisms.

Tropical and Subtropical Coniferous Forests

The tropical and subtropical coniferous forests biome is characterized by diverse species of conifer (needle-leaf) trees.This biome has a very limited distribution and is found mainly in Mexico, Central America, and on the islands of Cuba, Dominican Republic, and Haiti where low levels of precipitation and moderate temperature variability occurs. The needle-leaf form of these trees is an adaptation to drought. This biome shares some of the plant and animal species common to tropical and subtropical savanna, dry broadleaf forest, and moist broadleaf forest. Understory vegetation composed of shrubs and small trees is well developed and diverse. Finally, many species of migratory birds and butterflies spend their winter in this biome.

The Importance and
Conservation of Biomes
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 and aquatic, 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.
Aquatic 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.






SUMMARY
What is a biome?
A biome can be defined as a "major regional community of plants and animals with similar life forms and environmental conditions. It is the largest geographical biotic unit, and is named after the dominant type of life form, such as tropical rain forest, grassland, or coral reef."  The dominant life forms are usually conspicuous plants, or plant-like species such as corals. A single biome can be widely scattered about the planet. Due to similar pressures of natural selection, species in differ ent parts of a biome may converge in their appearance and behaviors, even when they do not share the same ancestors.
Terrestrial Biomes
Abiotic factors, such as climate, are important in determining where a particular biome is located. There are longtitudal patterns of climate over the Earth’s surface, and therefore, there are also longtitudal patterns of biome distribution over the Earth’s surface. 
Description: C:\Users\TMOT\Desktop\1HRT\1Hrt\biomes3_files\dot_clear.gif
Description: C:\Users\TMOT\Desktop\1HRT\1Hrt\biomes3_files\dot_clear.gif
Description: C:\Users\TMOT\Desktop\1HRT\1Hrt\biomes3_files\dot_clear.gif
Description: C:\Users\TMOT\Desktop\1HRT\1Hrt\biomes3_files\dot_clear.gif
Description: Tropical forest
Description: Savanna
Description: Desert
Description: Extreme Desert
Description: Chaparral
Description: Grassland
Description: Deciduous forest
Description: Taiga
Description: Tundra

Description: C:\Users\TMOT\Desktop\1HRT\1Hrt\biomes3_files\dot_clear.gif
 Biomes are often named for their predominant vegetation, and all have certain characteristics such as microorganisms, fungi, and animals which have adapted to their particular environment.  As well, biomes also grade into one another, and do not usually have sharp boundaries.  In fact, if the area of intergradation is large enough, it may itself be recognized as a separate biome. 
In biomes of the same type, but located in different areas, the species found there may vary.  For example, in the coniferous forests of North America, red spruce is common in the east, but is not found in other areas.  There, black spruce and white spruce are abundant.  Also, plants of different families are found in African and North American deserts, but the plants do resemble one another superficially.  This similarity can arise due to convergent evolution, “the independant development of similarity between species as a result of their having similar ecological roles and selection pressures. 
Several communities may be represented in patches within a biome.  For example, snowfall may break branches and small trees and cause openings in a coniferous forest, allowing deciduous species to grow.



                                                                                 












Posted by at

No comments:

Post a Comment

Subscribe to: Post Comments (Atom)