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A savanna, or savannah, is a grassland ecosystem characterized by the

trees being sufficiently small or widely spaced so that the canopy does not

close. The open canopy allows sufficient light to reach the ground to

support an unbroken herbaceous layer consisting primarily of C4 grasses.

[1] Some classification systems[which?] also recognize a grasslandsavanna from which trees are absent.[2] This article deals only with

savanna under the common definition of a grassy woodland with a

significant woody plant component.

It is often believed that savannas feature widely spaced,scattered trees. However, in many savannas, tree densitiesare higher and trees are more regularly spaced than inforest. Savannas are also characterized by seasonal wateravailability, with the majority of rainfall confined to oneseason. Savannas are associated with several types ofbiomes. Savannas are frequently in a transitional zonebetween forest and desert or prairie. Savanna coversapproximately 20% of the Earth's land area. The largest areaof savanna is in Africa.

Etymology

San Rafae Gran Sabana, Venezuela.

Although the term savanna is believed to have originally come froman Arawak word describing "land which is without trees but withmuchgrass either tall or short" (Oviedo y Valdes, 1535), by the late 1800sit was used to mean "land with both grass and trees". It now refers to landwith grass and either scattered trees or an open canopy of trees.

Spanish explorers familiar with the term "sabana" called the grasslandsthey found around the Orinoco River "llanos", as well as callingVenezuelan and Colombian grasslands by that specific term. "Cerrado"was used on the higher savannas of the Brazilian Central Plateau.[3]

Distribution

Many grassy landscapes and mixed communities of trees, shrubs, andgrasses were described as savanna before the middle of the 19th century,

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when the concept of a tropical savanna climate became established.The Kppen climate classification system was strongly influenced byeffects of temperature and precipitation upon tree growth, and his over-simplified assumptions resulted in a tropical savanna classificationconcept which resulted in it being considered as a "climatic climax"

formation. The common usage meaning to describe vegetation nowconflicts with a simplified yet widespread climatic concept meaning. Thedivergence has sometimes caused areas such as extensive savannasnorth and south of theCongo and Amazon Rivers to be excluded frommapped savanna categories.[3]

"Barrens" has been used almost interchangeably with savanna in differentparts of North America. Sometimes midwestern savanna were describedas "grassland with trees". Different authors have defined the lower limitsof savanna tree coverage as 5-10% and upper limits range from 25-80%of an area.[4]

Two factors common to all savanna environments are rainfall variationsfrom year to year, and dry season wildfires. Savannas around the worldare also dominated by tropical grasses which use the C4 typeof photosynthesis.[3] In the Americas, e.g. in Belize, Central America,savanna vegetation is similar from Mexico to South America and tothe Caribbean.[5] InNorth America nearby trees are of subtropical types,ranging from southwestern Pinyon pine to southeastern Longleaf Pine andnorthern chestnut oak.[4]

Threats

Changes in fire management

Savannas are subject to regular wildfires and the ecosystem appears tobe the result of human use of fire. For example, Native Americans createdthe Pre-Columbian savannas of North America by periodically burningwhere fire-resistant plants were the dominant species. [6] Pine barrens inscattered locations from New Jersey to coastal New England are remnantsof these savannas. Aboriginal burning appears to have been responsiblefor the widespread occurrence of savanna in tropical Australia and NewGuinea,[7] and savannas in India are a result of human fire use.[8] The maquis shrub savannas of the Mediterranean region were likewise

created and maintained by anthropogenic fire.[9]

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Prescribed burn; Wisconsin bur oak savanna

These fires are usually confined to the herbaceous layer and do little longterm damage to mature trees. However, these fires either kill or suppress

tree seedlings, thus preventing the establishment of a continuous treecanopy which would prevent further grass growth. Prior to Europeansettlement aboriginal land use practices, including fire, influencedvegetation[10] and may have maintained and modified savanna flora.[1][7] Ithas been suggested by many authors[10][11] that aboriginal burning createda structurally more open savanna landscape. Aboriginal burning certainlycreated a habitat mosaic that probably increased biodiversity andchanged the structure of woodlands and geographic range of numerouswoodland species.[7][10] It has been suggested by many authors[11][12] thatwith the removal or alteration of traditional burning regimes many

savannas are being replaced by forest and shrub thickets with littleherbaceous layer.

The consumption of herbage by introduced grazers in savanna woodlandshas led to a reduction in the amount of fuel available for burning andresulted in fewer and cooler fires.[13] The introduction of exoticpasture legumes has also led to a reduction in the need to burn toproduce a flush of green growth because legumes retain high nutrientlevels throughout the year, and because fires can have a negative impacton legume populations which causes a reluctance to burn.[14]

Grazing and browsing animals

Oak savanna, United States

The closed forests types such as broadleaf forests and rainforests areusually not grazed owing to the closed structure precluding grass growth,and hence offering little opportunity for grazing.[15] In contrast the openstructure of savannas allows the growth of a herbaceous layer and arecommonly used for grazing domestic livestock.[16] As a result much of theworld's savannas have undergone change as a result of grazing by sheep,goats and cattle, ranging from changes in pasture composition to woody

weed encroachment.[17]

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The removal of grass by grazing affects the woody plant component ofwoodland systems in two major ways. Grasses compete with woody plantsfor water in the topsoil and removal by grazing reduces this competitiveeffect, potentially boosting tree growth.[18] In addition to this effect theremoval of fuel reduces both the intensity and the frequency of fires which

may control woody plant species.[19]Grazing animals can have a moredirect effect on woody plants by the browsing of palatable woody species.

There is evidence that unpalatable woody plants have increased undergrazing in savannas.[20] Grazing also promotes the spread of weeds insavannas by the removal or reduction of the plants which would normallycompete with potential weeds and hinder establishment.[10] In addition tothis, cattle and horses are implicated in the spread of the seeds of weedspecies such as Prickly Acacia (Acacia nilotica) and Stylo(Stylosanthes spp.).[21] Alterations in savanna species composition broughtabout by grazing can alter ecosystem function, and are exacerbated by

overgrazing and poor land management practices.Introduced grazing animals can also affect soil condition through physicalcompaction and break-up of the soil caused by the hooves of animals andthrough the erosion effects caused by the removal of protective plantcover. Such effects are most likely to occur on land subjected to repeatedand heavy grazing.[22] The effects of overstocking are often worst on soilsof low fertility and in low rainfall areas below 500 mm, as most soilnutrients in these areas tend to be concentrated in the surface so anymovement of soils can lead to severe degradation. Alteration in soilstructure and nutrient levels affects the establishment, growth and

survival of plant species and in turn can lead to a change in woodlandstructure and composition.

Tree clearing

Large areas of savanna have been cleared of trees, and this clearing iscontinuing today. For example until recently 480,000 ha of savanna werecleared annually in Australia alone primarily to improve pastureproduction.[10] Substantial savanna areas have been cleared of woodyvegetation and much of the area that remains today is vegetation thathas been disturbed by either clearing or thinning at some point in thepast.

Clearing is carried out by the grazing industry in an attempt to increasethe quality and quantity of feed available for stock and to improve themanagement of livestock. The removal of trees from savanna landremoves the competition for water from the grasses present, and can leadto a two to fourfold increase in pasture production, as well as improvingthe quality of the feed available.[23] Since stock carrying capacity isstrongly correlated with herbage yield there can be major financialbenefits from the removal of trees.[24] The removal of trees also assistsgrazing management. For example in sheep grazing regions of dense treeand shrub cover harbours predators, leading to increased stock

losses[25] while woody plant cover hinders mustering in both sheep andcattle areas.[26]

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A number of techniques have been employed to clear or kill woody plantsin savannas. Early pastoralists used felling and girdling, the removal of aring of bark and sapwood, as a means of clearing land. [27] In the 1950sarboricides suitable for stem injection were developed. War-surplus heavymachinery was made available, and these were used for either pushing

timber, or for pulling using a chain and ball strung between two machines.These two new methods of timber control, along with the introduction andwidespread adoption of several new pasture grasses and legumespromoted a resurgence in tree clearing. The 1980s also saw the release ofsoil-applied arboricides, notably tebuthiuron, that could be utilised withoutcutting and injecting each individual tree.

In many ways "artificial" clearing, particularly pulling, mimics the effectsof fire and, in savannas adapted to regeneration after fire as mostQueensland savannas are, there is a similar response to that after fire.[28] Tree clearing in many savanna communities, although causing a

dramatic reduction in basal area and canopy cover, often leaves a highpercentage of woody plants alive either as seedlings too small to beaffected or as plants capable of re-sprouting from lignotubers and brokenstumps. A population of woody plants equal to half or more of the originalnumber often remains following pulling of eucalypt communities, even ifall the trees over 5 metres are uprooted completely.

Exotic plant species

A number of exotic plants species have been introduced to the savannasaround the world. Amongst the woody plant species are seriousenvironmental weeds such as Prickly Acacia (Acacia nilotica), Rubbervine(Cryptostegia grandiflora), Mesquite (Prosopis spp.), Lantana (Lantanacamara and L. montevidensis) and Prickly Pear (Opuntia spp.) A range ofherbaceous species have also been introduced to these woodlands, eitherdeliberately or accidentally including Rhodes grass andother Chloris species, Buffel grass (Cenchrus ciliaris), Giant rat's tail grass(Sporobolus pyramidalis) parthenium (Parthenium hysteropherus) andstylos (Stylosanthes spp.) and other legumes. These introductions havethe potential to significantly alter the structure and composition ofsavannas worldwide, and have already done so in many areas through anumber of processes including altering the fire regime, increasing grazing

pressure, competing with native vegetation and occupying previouslyvacant ecological niches. Other plant species include: white sage, spottedcactus, cotton seed, rosemary.

Climate change

There exists the possibility that human induced climate change in theform of the greenhouse effect may result in an alteration of the structureand function of savannas. Some autho]have suggested that savannas andgrasslands may become even more susceptible to woody plantencroachment as a result of greenhouse induced climate change.However, a recent case described a savanna increasing its range at theexpense of forest in response to climate variation, and potential exists for

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similar rapid, dramatic shifts in vegetation distribution as a result of globalclimate change, particularly at ecotones such as savannas so oftenrepresent]

THE EQUATORIAL REGION

DISTRIBUTION

The equatorial, hot, wet climate is found between 5 o north and 10 o

south of the equator. Its greatest extent is found in the lowlands of the

Amazon, the Congo, Malaysia and the East Indies. Further away from the

equator, the influence of the on-shore trade winds gives rise to a modified

type of equatorial climate with monsoonal influences. Within the tropics,

the equatorial highlands have a distinctly cooler climate, modified by

altitude, examples Jos in Nigeria, Cameroun Highlands in Malaysia, etc.

CLIMATE

Temperature: the most significant feature of the equatorial climate is its

great uniformity of temperature round the year. The mean monthly

temperatures are around 27oC (80 oF) with very little variation. There is

no winter, cloudiness and heavy rainfall help to moderate the daily

temperature, so that even the equator itself cannot be unbearable. Also

regular land and sea breezes help in keeping a truly equable climate. The

temperature range within the equatorial region are around 2 C (4 F) or

less for example Warri (Nigeria) has its hottest Month around 28 C (82F) and its collest month around 26 C (78 F), therefore having its annual

range around 2 C (4 F)

Precipitation: precipitation in the equatorial region is heavy, between 60

inches and 106 inches and is well distributed throughout the year. There

is no month without rain and there are two periods of maximum rainfall,

July and September, which occur shortly after the equinoxes. Least rain

falls at the January and December solstices. But this simple pattern may

be altered or changed by local conditions.

Below is a chart showing the annual precipitation of Ukpo town (Nigeria).

Due to the great heat in the equatorial belt, mornings are bright and

sunny and there is much evaporation and conventional air currents are

set up, followed by heavy downpours of Convectional rain in the

afternoons from the towering Cumulonbus cloud. Thunders and lightening

often accompany the torrential showers. The amount of rainfall recorded

in one afternoon may be as much as the deserts receive for the entire

year.

NATURAL VEGETATION

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Equatorial regions support a luxuriant type of dense vegetation (the

tropical rain forest) because of the very heavy rainfall (over 80 inches)

and uniformly high temperature (27 C / 80 F). In the Amazon lowlands,

the forest is so dense and so complete in its vegetation extravagance. The

growing season in equatorial region is not restricted by either drought orcold, planting is down throughout the year.

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Temperate Grasslands

Introduction. Temperate grasslands are composed of a rich mix ofgrasses and forbs and underlain by some of the world's most fertile soils.Since the development of the steel plow most have been converted toagricultural lands.

Climate: Semiarid, continental climates of the middle latitudes(Koeppen's BSk climate type) typically have between 10 and 20 inches ofprecipitation a year. Much of this falls as snow, serving as reservoir ofmoisture for the beginning of the growing season. Warm to hot summersare experienced, depending on latitude.

Vegetation. Perennial grasses and perennial forbs [especiallyCompositae (or Asteraceae, depending on the taxonomic system used)and Leguminosae--the sunflower and pea families, respectively] aredominant growthforms. Two or more strata of grasses (erect grasses andrecumbent species) are recognized in the more humid expressions of thebiome.

Grasses. Perennial grasses, with their growth buds at or just below

the surface, are well-adapted to drought, fire, and cold. The tiller or

narrow, upright stem reduces heat-gain in the hot summers; theintricate root systems trap moisture and nutrients. Two basic types

are:

o Turf- or sod-forming grasses, with rhizomes or undergroundstems from which new plants spring forth; associated with themore humid grasslands

o Bunch grasses, without rhizomes, that reproduce by seed;associated with the drier parts of the biome.

Major regional expressions.

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North America: the prairies of the Central Lowlands and High Plainsof the US and Canada. The Palouse Prairie of eastern Washingtonstate, the California grasslands, and the desert grasslands of theSouthwest are also temperate grasslands.

Eurasia: the steppes from Ukraine eastward through Russia and

Mongolia. South America: the pampas of Argentina and Uruguay Africa: the veld in the Republic of South Africa.

Soils. Calcification is the dominant soil-forming process in semiaridregions. Mild leaching, high organic content, and concentration of calciumcarbonate in the B horizon typifies the dark brown mollisols developedunder the temperate grasslands. When this process works on a loess thatitself is rich in calcium, the world's most fertile soils are created, the

chernozems (A Russian term meaning black soil). Loess and hencechernozem underlie the eastern prairies of the US, the pampas of SouthAmerica, and the steppes of Ukraine and Russia.

Fauna. The temperate grassland fauna is very low in diversity, especiallyin comparison with the tropical grasslands or savannas of Africa. In NorthAmerica the dominant herbivores are bison Bison bison) and pronghorn(the sole member of the Nearctic endemic family, Antilocapridae). Rodentherbivores include the pocket gopher (another Nearctic endemic), groundsquirrels, and the prairie dog. Carnivores include coyote (actually an

omnivore), badger, and the federally endangered black-footed ferret, thelast two members of the weasel family.

On the Russian steppes the fauna formerly included wisent (Bisonbonasus), tarpan or wild horse, and saiga antelope, among others. Molerats, fossorial members of one of the two mammal families endemic to thePalearctic, are conspicuous by virtue their many mounds. Polecats andother members of the weasel family are among the larger, extantcarnivores.

Temperate coniferous forest is a terrestrial biome found

in temperate regions of the world with warm summers andcool winters and adequate rainfallto sustain a forest. In most temperate

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coniferous forests, evergreen conifers predominate, while some are a mixof conifers and broadleaf evergreentrees and/orbroadleaf deciduous trees. Temperate evergreen forests are common inthe coastal areas of regions that have mild winters and heavy rainfall, orinland in drier climates or mountain areas. Many species of trees inhabit

these forests including cedar, cypress, douglas-fir, fir, juniper, kauri,pine, podocarpus, spruce, redwood and yew. Theunderstory also contains a wide variety of herbaceous and shrub species.

A pine forest is an example of a temperate coniferous forest

Structurally, these forests are rather simple, generally consisting of two

layers: an overstory and understory. Some forests may support anintermediate layer of shrubs. Pine forests support an herbaceousunderstory that is generally dominated by grasses and herbaceousperennials, and are often subject to ecologically important wildfires.

Carpathian montane conifer forest,Slovakia

Temperate rain forests occur only in seven regions around the world:the Pacific temperate rain forests of thePacific Northwest, the Valdiviantemperate rain forests of southwestern South America, the rain forestsofNew Zealand and Tasmania, northwest Europe (small pockets

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in Ireland, Scotland, Wales, Iceland and a somewhat larger areain Norway), southern Japan, and the eastern Black Sea-Caspian Sea regionof Turkeyand Georgia to northern Iran. The moist conditions of temperaterain forests generally support an understory of mosses, ferns and someshrubs. Temperate rain forests can be temperate coniferous forests

or temperate broadleaf and mixed forests.

The temperate coniferous rain forests sustain the highest levels ofbiomass in any terrestrial ecosystem and are notable for trees of massiveproportions, including Giant Sequoia (Sequoiadendron gigantea), CoastRedwood (Sequoia sempervirens), Douglas-fir (Pseudotsugamenziesii), Sitka Spruce (Picea sitchensis), Alerce (Fitzroya cupressoides)and Kauri (Agathis australis). These forests are quite rare, occurring insmall areas of North America, southwestern South America and northernNew Zealand. TheKlamath-Siskiyou forests of northwestern California andsouthwestern Oregon is known for its rich variety of plant and animal

species, including many endemic species

The Coniferous Forest is a forest of

Conifers (too much to handle, isn't it?). A Conifer is a tree that produces

its seeds in cones. The Pine tree is the most common example. Conifer

leaves conserve water with the thick, waxy layer that covers their leaves,

also known as needles. The vegitation in the Coniferous forest is small in

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size, but large enough to feed the vast herbivore population. Most of

these animals survive the brutal winters by migrating or hibernating.

Average Annual Rainfall- 14-29.5 in.

Average Temperatures in the Summer- 57.2FAverage Temperatures in the Winter- 14FPLANTSMany softwood trees such as fir, pine, spruce, and hemlock.ANIMALSMost animals are herbivores, however some carnivores and omnivores arethrown in. Animals in Coniferous Forests include the red fox, moose,snowshoe hare, great horned owl, and the crossbill.

FUN FACTSThe largest Carniferous forest exists in a ring in Alaska, Canada, northernEurope, and northern Asia, in a ring in the Northern Hemisphere. Thisforest is called the "Taiga".Most of the world's commercial softwood timber, used for paper, comesfrom the Taiga.Coniferous Forests are the largest land Biome of the World.

THUNDRA REGION

In physical geography, tundra is a biome where the tree growth ishindered by low temperatures and short growing seasons. Theterm tundra comes through Russian from the KildinSami word t ndr "uplands," "treeless mountain tract."[1] There are threetypes of tundra: Arctic tundra,[2]alpine tundra,[2] and Antarctictundra.[3] In tundra, the vegetation is composed of dwarf shrubs, sedges and grasses, mosses, and lichens. Scattered treesgrow in some tundra. The ecotone (or ecological boundary region)

between the tundra and the forest is known as the tree line or timberline.

Arctic

Arctic tundra occurs in the far Northern Hemisphere, north ofthe taiga belt. The word "tundra" usually refers only to the areas wherethe subsoil is permafrost, or permanently frozen soil. (It may also refer tothe treeless plain in general, so that northernSpmi would be included.)Permafrost tundra includes vast areas of northern Russia and Canada.[2] The polar tundra is home to several peoples who aremostly nomadic reindeer herders, such as the Nganasan and Nenets in

the permafrost area (and theSami in Spmi).

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Arctic tundra contains areas of stark landscape and is frozen for much ofthe year. The soil there is frozen from 2590 cm (9.835.4 inches) down,and it is impossible for trees to grow. Instead, bare and sometimes rockyland can only support low growing plants such as moss, heath(Ericaceae varieties such as crowberry and black bearberry), and lichen.

There are two main seasons, winter and summer, in the polar tundraareas. During the winter it is very cold and dark, with the averagetemperature around 28 C (18 F), sometimes dipping as low as 50C (58 F). However, extreme cold temperatures on the tundra do notdrop as low as those experienced in taiga areas further south (forexample, Russia's and Canada's lowest temperatures were recorded inlocations south of the tree line). During the summer, temperatures risesomewhat, and the top layer of the permafrost melts, leaving the groundvery soggy. The tundra is covered in marshes, lakes, bogs and streamsduring the warm months. Generally daytime temperatures during the

summer rise to about 12 C (54 F) but can often drop to 3 C (37 F) oreven below freezing. Arctic tundras are sometimes the subjectof habitat conservation programs. In Canada and Russia, many of theseareas are protected through a national Biodiversity Action Plan.

Tundra in Alaska

The tundra is a very windy area, with winds often blowing upwards of 4897 km/h (3060 miles an hour). However, in terms of precipitation, it isdesert-like, with only about 1525 cm (610 inches) falling per year (the

summer is typically the season of maximum precipitation). Althoughprecipitation is light, evaporation is also relatively minimal. During thesummer, the permafrost thaws just enough to let plants grow andreproduce, but because the ground below this is frozen, the water cannotsink any lower, and so the water forms the lakes and marshes foundduring the summer months. There is a natural pattern of accumulation offuel and wildfire which varies depending on the nature of vegetation andterrain. Research in Alaska has shown fire-event return intervals, (FRIs)that typically vary from 150 to 200 years with dryer lowland areas burningmore frequently than wetter highland areas.[4]

The biodiversity of the tundras is low: 1,700 species of vascular plants andonly 48 land mammals can be found, although millions of birds migrate

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there each year for the marshes.[5] There are also a few fish species suchas the flatfish. There are few species with large populations. Notableanimals in the Arctic tundra include caribou (reindeer), musk ox, arctichare, arctic fox, snowy owl, lemmings, and polar bears (only the extremenorth).[6] Tundra is largely devoid of poikilotherms such as frogs or lizards.

Due to the harsh climate of the Arctic tundra, regions of this kind haveseen little human activity, even though they are sometimes rich in naturalresources such as oil and uranium. In recent times this has begun tochange in Alaska, Russia, and some other parts of the world.

Relationship with global warming

A severe threat to the tundras, specifically to the permafrost, is globalwarming. The melting of the permafrost in a given area on human timescales (decades or centuries) could radically change which species cansurvive there.[7]

Another concern is that about one third of the world's soil-bound carbon isin taiga and tundra areas. When the permafrost melts, it releases carbonin the form of carbon dioxide andmethane,[8] both of whichare greenhouse gases. The effect has been observed in Alaska. In the1970s the tundra was a carbon sink, but today, it is a carbon source.[9] Methane is produced when vegetation decays in lakes and wetlands.[10]

The amount of greenhouse gases which will be released under projectedscenarios for global warming have not been reliably quantified byscientific studies, although a few studies were reported to be underway in2011. It is uncertain whether the impact of increased greenhouse gases

from this source will be minimal or massive.[10]

In locations where dead vegetation and peat has accumulated there is arisk of wildfire such as the 1,039 square kilometres (401 sq mi) of tundrawhich burned in 2007 on the north slope of the Brooks range. [10] Suchevents may both result from and contribute to global warming.[11]

Antarctic

Tundra on the Pninsule Rallier du Baty, Kerguelen Islands.

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Antarctic tundra occurs on Antarctica and on several Antarctic andsubantarctic islands, including South Georgia and the South SandwichIslands and the Kerguelen Islands. Most of Antarctica is too cold and dry tosupport vegetation, and most of the continent is covered by ice fields.However, some portions of the continent, particularly the Antarctic

Peninsula, have areas of rocky soil that support plant life. The florapresently consists of around 300400 lichens, 100 mosses, 25 liverworts,and around 700 terrestrial and aquatic algae species, which live on theareas of exposed rock and soil around the shore of the continent.Antarctica's two flowering plant species, the Antarctic hairgrass(Deschampsia antarctica) and Antarctic pearlwort (Colobanthusquitensis), are found on the northern and western parts of the AntarcticPeninsula.[12]

In contrast with the Arctic tundra, the Antarctic tundra lacks a largemammal fauna, mostly due to its physical isolation from the other

continents. Sea mammals and sea birds, including seals and penguins,inhabit areas near the shore, and some small mammals,like rabbitsand cats, have been introduced by humans to some of thesubantarctic islands. The Antipodes Subantarctic Islandstundra ecoregion includes the Bounty Islands, Auckland Islands, AntipodesIslands, the Campbell Island group, and Macquarie Island.[13] Speciesendemic to this ecoregion include Nematocerasdienemum and Nematoceras sulcatum, the only Subantarctic orchids;the royal penguin; and the Antipodean albatross.[13]

The flora and fauna of Antarctica and the Antarctic Islands (south of 60

south latitude) are protected by the Antarctic Treaty.[14]

Alpine

Hikers traversing the Franconia Ridge in the White Mountains, New

Hampshire, United States, much of which is in the alpine zone.

Main article: Alpine tundra

Alpine tundra does not contain trees because it is at high altitude. Alpinetundra is distinguished from arctic tundra in that alpine tundra typically

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does not have permafrost, and alpine soils are generally better drainedthan arctic soils. Alpine tundra transitions to subalpine forests belowthe tree line; stunted forests occurring at the forest-tundra ecotone areknown as Krummholz.

Alpine tundra occurs in mountains worldwide. The flora of the alpinetundra is characterized by dwarf shrubs close to the ground. The coldclimate of the alpine tundra is caused by the low air pressure, and issimilar to polar climate.

Climatic classification

Tundra region with fjords, glaciers and mountains.

Kongsfjorden, Spitsbergen.

Tundra climates ordinarily fit the Kppen climate classification ET,signifying a local climate in which at least one month has an averagetemperature high enough to melt snow (0C or 32F), but no month withan average temperature in excess of (10C/50F). The cold limit generallymeets theEF climates of permanent ice and snows; the warm-summerlimit generally corresponds with the poleward or altitudinal limit of trees,where they grade into the subarcticclimates designated Dfd and Dwd (extreme winters as in partsof Siberia), Dfc typical in Alaska, Canada,European Russia, and Western

Siberia (cold winters with months of freezing), or even Cfc (no monthcolder than -3C as in parts of Iceland and southernmost South America).

Tundra climates as a rule are hostile to woody vegetation even where thewinters are comparatively mild by polar standards, as in Iceland.

Despite the potential diversity of climates in the ET category involvingprecipitation, extreme temperatures, and relative wet and dry seasons,this category is rarely subdivided. Rainfall and snowfall are generallyslight due to the low vapor pressure of water in the chilly atmosphere, butas a rule potential evapotranspiration is extremely low, allowing soggyterrain of swamps and bogs even in places that get precipitation typical

of deserts of lower and middle latitudes. The amount of native tundra

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biomass depends more on the local temperature than the amount ofprecipitation.

Economy

Human economic activity has been scarce on tundras. Hunting, trapping

and reindeer have provided food and hides to the local population.Occasional mineral resources, such as fossil fuel and ores occasionallyappear in tundras. Difficultues of prospecting, mining and transportationhave held back exploitation of these resources until modern tim

DROUGHT

Drought is a feature of climate that is defined as a period of below-average rainfall sufficiently long and intense to result in seriousenvironmental and socioeconomic stresses, such as crop failures and

water shortages, in the affected area. Droughts can occur in any climaticregion, but their characteristics vary considerably among regions. Whatdroughts in all climatic regions have in common is their gradual onset,whichin contrast to other natural hazardsmakes their beginning andend difficult to identify. Defined primarily as natural phenomena, droughtshave not received much attention in the social sciences. Only since the1990s, with the increasing appreciation of the linkages between theenvironment and society, have droughts begun to be viewed as an issueof interest also for the social sciences.

Drought is caused by the sinking motion of air in a high-pressure cell,

which results in decreasing relative humidity of the air and little or noprecipitation. Most climatic regions are temporarily under the influence ofhigh pressure; droughts occur only when atmospheric circulation patternsthat cause the high pressure persist or recur persistently over anunusually long period of time. Because of the global nature of atmosphericcirculation, explanations for anomalous circulation patterns extend farbeyond the drought-affected area. Thus global patterns of atmosphericpressure systems and sea surface temperatures have been invoked toexplain the occurrence of periodically recurring drought events in someparts of the globe. Most prominent among those global patterns is the ElNio Southern Oscillation (ENSO), a coupled ocean-atmosphere anomalythat originates in the Pacific basin but has repercussions on the climaticconditions in areas as far apart as southern Africa, India, and Brazil.Anthropogenic processes that lead to changes in land cover, such asdeforestation and overgrazing, affect local-scale moisture recycling andcan induce local reductions in rainfall. Although simulation models haveshown the possibility of substantial reductions in rainfall resulting fromland-cover change, anthropogenic disturbances large enough to explainmore than local-scale reductions in rainfall have not been observed.

TYPES OF DROUGHT

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The effects of drought on environment, economy, and society aremanifold. In order of the increasing severity and scope of their impacts,four types of drought are commonly distinguished: A meteorologicaldroughtmanifests itself in a shortfall of precipitation or changes inprecipitation intensity and timing, possibly aggravated by other climatic

factors, such as high temperatures and winds. Risks associated with thistype of drought include wildfire hazard and reduced water infiltration intothe soil. If the drought persists long enough to result in significant soilwater deficits and plant water stress, it crosses the threshold intoanagricultural drought. Lower crop yields and quality, as well as increasedsoil erosion and dust emission, are possible impacts expected from thistype of drought.

Because various crops differ in their water demand, a farmers choice ofcrop type can either buffer or exacerbate the effects of an agriculturaldrought. A drought is classified as a hydrological drought once the

precipitation shortfall affects surface and subsurface water supplies.Hydrological droughts usually lag behind the occurrence of meteorologicaldroughts because of the time needed for precipitation deficits to reach thesurface and groundwater levels of the water cycle. Their impacts, whichconsequently are also out of phase with those of a meteorological andagricultural drought, include reduced stream flow, below-normal reservoirand lake levels, loss of wetlands, and declining water quality. Althoughclimate is the primary factor of a hydrological drought, humans contributeto its effects by changes in land and water use, such as urbanization andthe construction of dams. Finally, a socioeconomic drought occurs when

the supply of economic goods and services, including water, forage, food,and hydroelectric power, can no longer be met for drought-related causes.Farmers and ranchers, who depend on agricultural and pastureproductivity, are the first to suffer losses. Then follow industriesdepending on agricultural production. As a result, consumers may have topay more for their food and other weather-sensitive products andservices.

The socioeconomic effects of a drought vary not only in proportion to theseverity of the climatological event but also depending on thevulnerability of the affected population. Monetary costs arise for any

economy hit by drought, such as to cover for lost crops, crop insurancepayouts, and fire damage; but only in the most vulnerable populations ofthe developing world are drought effectsfood insecurity, famine, healthproblems, and loss of life and livelihoodsoften paired with economic,social, and political difficulties. Subsistence farmers and pastoralists inparticular suffer from crop and livestock losses, as well as from increasedfood prices. Droughts force many of them to migrate from rural to urbanareas, increasing pressure on resources there.

COPING WITH DROUGHT

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Scientists and decision-makers have devised a number of ways to dealwith drought, which can be grouped into drought monitoring, forecasting,and mitigation. Meteorologists around the world carefully monitormeteorological and hydrological variables (precipitation patterns, soilmoisture, stream flow) over time to determine the onset and end of a

drought. Satellite remote sensing technology has contributed immenselyto quantitative monitoring over large geographic areas. Understanding thecomplex physical aspects leading to droughts is a prerequisite for makingincreasingly reliable and credible drought predictions. Empirical studieshave shown that drought results from a complex interplay of differentclimatological factors, which makes forecasting difficult. In the tropics,where scientists have made significant advances in understanding theclimate system, the potential for seasonal drought predictions ispromising, particularly with respect to droughts related to ENSO. Multiyeardroughts as well as droughts outside the tropics still cannot be predicted

with a level of accuracy that is without risk for the users of thosepredictions. Knowing the frequency, duration, and spatial extent of pastdroughts, however, helps in determining the likelihood and potentialseverity of future droughts.

In addition to the assessment of meteorological processes, droughtmitigation also requires an understanding of the vulnerabilities of differentpopulation groups to drought. Mitigation tools range from early warningsystems, which monitor both meteorological conditions and vulnerablepopulations (e.g., the Famine Early Warning Systems Network, operatingin Africa, Central America, and Afghanistan), to various forms of weather-

related crop insurance schemes (e.g., in the United States and Australiaamong others), emergency water supply augmentation (e.g., tapping newwater resources), and water demand reduction (e.g., by means ofeconomic incentives for water conservation, improvement of water useefficiencies, breeding for drought tolerance, diversification to lessweather-dependent economic activities, and public water conservationawareness programs). As droughts are expected to become morefrequent and more extreme with global warming, it is imperative toimprove drought mitigation efforts and increase future droughtpreparedness.

FLOODA flood is an overflow of an expanse of water that submerges land.[1] The European Union (EU) Floods Directive defines a flood as a coveringby water of land not normally covered by water.[2] In the sense of "flowingwater", the word may also be applied to the inflow of the tide. Floodingmay result from the volume of water within a body of water, such asa river or lake, which overflows or breaks levees, with the result that someof the water escapes its usual boundaries.[3]

While the size of a lake or other body of water will vary with seasonalchanges in precipitation and snow melt, it is not a significant flood unless

such escapes of water endanger land areas used by man like a village,city or other inhabited area.

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Floods can also occur in rivers, when flow exceeds the capacity of theriver channel, particularly at bends or meanders. Floods often causedamage to homes and businesses if they are placed in natural flood plainsof rivers. While flood damage can be virtually eliminated by moving awayfrom rivers and other bodies of water, since time out of mind, people have

lived and worked by the water to seek sustenance and capitalize on thegains of cheap and easy travel and commerce by being near water. Thathumans continue to inhabit areas threatened by flood damage is evidencethat the perceived value of living near the water exceeds the cost ofrepeated periodic flooding.

The word "flood" comes from the Old English flod, a word common toGermanic languages (compare German Flut, Dutch vloed from the sameroot as is seen in flow, float; also compare withLatin fluctus, flumen). Deluge myths are mythical stories of a great floodsent by a deity or deities to destroy civilization as an act of divine

retribution, and are featured in the mythology of many cultures.

Below is a list of the deadliest floods worldwide, showing events with

death tolls at or above 100,000 individuals.

Death toll Event Location Date

2,500,0003,700,000[21]

1931 China floods China 1931

900,0002,000,000

1887 Yellow River (HuangHe) flood

China 1887

500,000700,000

1938 Yellow River (HuangHe) flood

China 1938

231,000

Banqiao Dam failure, resultof Typhoon Nina.Approximately 86,000people died from floodingand another 145,000 diedduring subsequent disease.

China 1975

230,000 Indian Ocean tsunami Indonesia 2004

145,000 1935 Yangtze river flood China 1935100,000+ St. Felix's Flood, storm surge Netherlands 1530

100,000Hanoi and Red RiverDelta flood

North Vietnam1971

100,000 1911 Yangtze river flood China1911

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How does Shakespeare present the two different worlds of Court life and

the rural idyll of the 'Golden Age' in As You Like It? As You Like It is a

pastoral piece of literature and this form of literature thrives on the

contrast between life in the city and life in the country. Typically, it

suggests that the oppression from the Court can be remedied by a tripinto the country's therapeutic woods which in this case refers to the

Forest of Arden and that a person's sense of balance and rightness can be

restored by the uncorrupted shepherds and shepherdesses. This restored

rightness enables one to return to the Court a better person. In this play

the character of whom this affects is Oliver de Boys Although Shakespeare

tests the bounds of these conventions, the shepherdess Audrey as an

example, is neither articulate nor pure. He begins As You Like It by

establishing the city/country dichotomy on which the pastoral mood

depends. The play ends with Shakespeare reminding us that life in the

country is solely a temporary affair. I have gathered this because as the

characters prepare to return to life at court, they do not rank the country

over Court or vice versa, but instead they suggest a delicate balance

between the two as too much of one thing is seen as being negative. They

give the impression that the simplicity of the forest provides shelter from

the strains of Court life, but they also display the need for Court and the

sophistication it brings. Life in the Court, and life in the country. These

were two very different things during the 'Golden Age.' The 'Golden Age' is

represented by the world of the country, but not the Court. It is the

classical time of pastoral perfection where there was no natural decay, nopassing of seasons, the world seemed timeless and was peopled by

shepherds and shepherdesses along with their sheep. It has also been

compared to The Garden of Eden in the Bible, hence, showing its idyllic

qualities before 'Man' sinned. Life in the Court however was completely

different in contrast. Life in the Court was a place of corruption and,

sometimes anarchy as shown by the usurption of Duke Seniors throne by

his younger brother Duke Frederick. Usurption of a throne shows a total

disregard for all laws and therefore, can make people feel as though they

one of the major themes of As You Like It is the contrast between country

and court life with debates focussing on different points of view.

the first of these comes when duke senior describes how, at Arden, he

could see 'toungues in trees", "sermons in stones" and had no enemy

except the harshness of the elements of nature- "churlish chiding of the

winter's wind". the pastoral existence was devoid of the "painted pomp"back at court which shows the carefree, pleasurable lifestyle that the duke

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was enjoying in Arden in contrast to the constant public haunt that he

had to go through prior to his banishment. the words are romanticized and

the mood is set for the rest of the play. Despite some natural perils, there

was 'good in everything'. this tilts the argument in favor of pastoral

existence. Shakespeare highlights the educational, edifying andenlightening nature of this foray into the woods.

The argument between Touchstone and corin is also crucial in this regard

and although touchstone wins over and Corin chooses to back out, it is

obvious that Touchstone's points of argument are merely farcical and

domineering whereas Corin's simple but logical rationale leaves more of

an impact. Even Corin's admission of defeat does not mean that courtly

manners are superior in fact it only showcases Corins sensibility inacknowledging that both of these co-exist and there are some acceptable

norms at court which may seem ridiculous in the forest while some forest

customs could prove to be inappropriate for the city.

Shakespeare also balances his showcasing of the advantages of pastoralverve by presenting some of its negative aspects and its ignorance forinstance, the hauteur of the shepherdess Pheobe, Silvius blind and stupidaffections and his unrealistic speech in verse.