thumb|right|400px|Worldwide zones of Tropical savanna climate (Aw).Tropical savanna climate or tropical wet and dry climate is a type of climate that corresponds to the Köppen climate classification categories "Aw" and '"As."

Description

These climates have monthly mean temperature above 18°C in every month of the year and typically a pronounced dry season, with the driest month having precipitation less than 60 mm and also less than (100 − [total annual precipitation {mm}/25]). This latter fact is in direct contrast to a tropical monsoon climate, whose driest month sees less than 60 mm of precipitation but has ''more'' than (100 – [total annual precipitation {mm}/25]). In essence, a tropical savanna climate tends to either see less rainfall than a tropical monsoon climate or have more pronounced dry seasons than a tropical monsoon climate.

Distribution

Most places that have this climate are found at the outer margins of the tropical zone, but occasionally an inner-tropical location (e.g., San Marcos, Antioquia, Colombia) also qualifies. Similarly, the Caribbean coast, eastward from the Gulf of Urabá on the Colombia–Panamá border to the Orinoco river delta, on the Atlantic ocean (ca. 4,000 km), have long dry periods (the extreme is the BSh climate (see below), characterised by very low, unreliable precipitation, present, for instance, in extensive areas in the Guajira, and Coro, western Venezuela, the northernmost peninsulas in South America, which receive <300 mm total annual precipitation, practically all in two or three months). This condition extends to the Lesser Antilles and Greater Antilles forming the Circumcaribbean dry belt. The length and severity of the dry season diminishes inland (southward); at the latitude of the Amazon river — which flows eastward, just south of the equatorial line — the climate is Af. East from the Andes, between the dry, arid Caribbean and the ever-wet Amazon are the Orinoco river' llanos or savannas, from where this climate takes its name.

Sometimes ''As'' is used in place of ''Aw'' if the dry season occurs during the time of higher sun and longer days. This is the case in parts of Hawaii, East Africa (Mombasa, Kenya), Sri Lanka (Trincomalee) and coastal regions of Northeastern Brazil (from Natal to Maceió), for instance. In most places that have tropical wet and dry climates, however, the dry season occurs during the time of lower sun and shorter days because of rainshadow effects during the 'high-sun' part of the year.

Charts of selected cities

See also

Tropics

Köppen climate classification

Tropical marine climate

Category:Climate Category:Köppen climate classifications Category:Tropics

ar:سافانا bs:Savana bg:Савана ca:Sabana cv:Саванна cs:Savana da:Savanne de:Savanne et:Savann es:Clima tropical seco eo:Savano eu:Sabana fr:Climat tropical de savane fy:Savanne gl:Sabana ko:사바나 기후 hr:Savana io:Savano id:Sabana it:Clima della savana he:סוואנה ka:სავანა sw:Savana lv:Savanna lt:Savana hu:Szavanna ml:സവേന ms:Iklim savana tropika nl:Tropisch savanneklimaat ja:サバナ気候 no:Savanne nn:Tropisk savanneklima pl:Sawanna pt:Clima tropical com estação seca ro:Savană ru:Саванна sq:Savana simple:Savanna sk:Savana sl:Savansko podnebje sr:Савана sh:Tropska savanska klima fi:Savanni sv:Savann tr:Savan uk:Савана zh:熱帶乾濕季氣候

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. Some classification systems also recognize a grassland savanna from which trees are absent. 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 densities are higher and trees are more regularly spaced than in forest. Savannas are also characterized by seasonal water availability, with the majority of rainfall confined to one season. Savannas are associated with several types of biomes. Savannas are frequently in a transitional zone between forest and desert or prairie. Savanna covers approximately 20% of the Earth's land area. The largest area of savanna is in Africa.

Definitions and distributions

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

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

Many grassy landscapes and mixed communities of trees, shrubs, and grasses were described as savanna before the middle of the 19th century, when the concept of a tropical savanna climate became established. The Köppen climate classification system was strongly influenced by effects of temperature and precipitation upon tree growth, and his over-simplified assumptions resulted in a tropical savanna classification concept which resulted in it being considered as a "climatic climax" formation. The common usage meaning to describe vegetation now conflicts with a simplified yet widespread climatic concept meaning. The divergence has sometimes caused areas such as extensive savannas north and south of the Congo and Amazon Rivers to be excluded from mapped savanna categories.

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

Two factors common to all savanna environments are rainfall variations from year to year, and dry season wildfires. Savannas around the world are also dominated by tropical grasses which use the C4 type of photosynthesis. In the Americas, e.g. in Belize, Central America, savanna vegetation is similar from Mexico to South America and to the Caribbean. In North America nearby trees are of subtropical types, ranging from southwestern Pinyon pine to southeastern Longleaf Pine and northern chestnut oak.

Threats

Changes in fire management

Savannas are subject to regular wildfires and the ecosystem appears to be the result of human use of fire. For example, Native Americans created the Pre-Columbian savannas of North America by periodically burning where fire-resistant plants were the dominant species. Pine barrens in scattered locations from New Jersey to coastal New England are remnants of these savannas. Aboriginal burning appears to have been responsible for the widespread occurrence of savanna in tropical Australia and New Guinea, and savannas in India are a result of human fire use. The maquis shrub savannas of the Mediterranean region were likewise created and maintained by anthropogenic fire.

These fires are usually confined to the herbaceous layer and do little long term damage to mature trees. However, these fires either kill or suppress tree seedlings, thus preventing the establishment of a continuous tree canopy which would prevent further grass growth. Prior to European settlement aboriginal land use practices, including fire, influenced vegetation and may have maintained and modified savanna flora. It has been suggested by many authors that aboriginal burning created a structurally more open savanna landscape. Aboriginal burning certainly created a habitat mosaic that probably increased biodiversity and changed the structure of woodlands and geographic range of numerous woodland species. It has been suggested by many authors that with the removal or alteration of traditional burning regimes many savannas are being replaced by forest and shrub thickets with little herbaceous layer.

The consumption of herbage by introduced grazers in savanna woodlands has led to a reduction in the amount of fuel available for burning and resulted in fewer and cooler fires. The introduction of exotic pasture legumes has also led to a reduction in the need to burn to produce a flush of green growth because legumes retain high nutrient levels throughout the year, and because fires can have a negative impact on legume populations which causes a reluctance to burn.

Grazing and browsing animals

The closed forests types such as broadleaf forests and rainforests are usually not grazed owing to the closed structure precluding grass growth, and hence offering little opportunity for grazing. In contrast the open structure of savannas allows the growth of a herbaceous layer and are commonly used for grazing domestic livestock. As a result much of the world'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.

The removal of grass by grazing affects the woody plant component of woodland systems in two major ways. Grasses compete with woody plants for water in the topsoil and removal by grazing reduces this competitive effect, potentially boosting tree growth. In addition to this effect the removal of fuel reduces both the intensity and the frequency of fires which may control woody plant species. Grazing animals can have a more direct effect on woody plants by the browsing of palatable woody species. There is evidence that unpalatable woody plants have increased under grazing in savannas. Grazing also promotes the spread of weeds in savannas by the removal or reduction of the plants which would normally compete with potential weeds and hinder establishment. In addition to this, cattle and horses are implicated in the spread of the seeds of weed species such as Prickly Acacia (''Acacia nilotica'') and Stylo (''Stylosanthes'' spp.). Alterations in savanna species composition brought about 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 physical compaction and break-up of the soil caused by the hooves of animals and through the erosion effects caused by the removal of protective plant cover. Such effects are most likely to occur on land subjected to repeated and heavy grazing. The effects of overstocking are often worst on soils of low fertility and in low rainfall areas below 500 mm, as most soil nutrients in these areas tend to be concentrated in the surface so any movement of soils can lead to severe degradation. Alteration in soil structure and nutrient levels affects the establishment, growth and survival of plant species and in turn can lead to a change in woodland structure and composition.

Tree clearing

Large areas of savanna have been cleared of trees, and this clearing is continuing today. For example until recently 480,000 ha of savanna were cleared annually in Australia alone primarily to improve pasture production. Substantial savanna areas have been cleared of woody vegetation and much of the area that remains today is vegetation that has been disturbed by either clearing or thinning at some point in the past.

Clearing is carried out by the grazing industry in an attempt to increase the quality and quantity of feed available for stock and to improve the management of livestock. The removal of trees from savanna land removes the competition for water from the grasses present, and can lead to a two to fourfold increase in pasture production, as well as improving the quality of the feed available. Since stock carrying capacity is strongly correlated with herbage yield there can be major financial benefits from the removal of trees. The removal of trees also assists grazing management. For example in sheep grazing regions of dense tree and shrub cover harbours predators, leading to increased stock losses while woody plant cover hinders mustering in both sheep and cattle areas.

A number of techniques have been employed to clear or kill woody plants in savannas. Early pastoralists used felling and girdling, the removal of a ring of bark and sapwood, as a means of clearing land. In the 1950s arboricides suitable for stem injection were developed. War-surplus heavy machinery 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 and widespread adoption of several new pasture grasses and legumes promoted a resurgence in tree clearing. The 1980s also saw the release of soil-applied arboricides, notably tebuthiuron, that could be utilised without cutting and injecting each individual tree.

In many ways "artificial" clearing, particularly pulling, mimics the effects of fire and, in savannas adapted to regeneration after fire as most Queensland savannas are, there is a similar response to that after fire. Tree clearing in many savanna communities, although causing a dramatic reduction in basal area and canopy cover, often leaves a high percentage of woody plants alive either as seedlings too small to be affected or as plants capable of re-sprouting from lignotubers and broken stumps. A population of woody plants equal to half or more of the original number often remains following pulling of eucalypt communities, even if all the trees over 5 metres are uprooted completely.

Exotic plant species

A number of exotic plants species have been introduced to the savannas around the world. Amongst the woody plant species are serious environmental weeds such as Prickly Acacia (''Acacia nilotica''), Rubbervine (''Cryptostegia grandiflora''), Mesquite (''Prosopis'' spp.), Lantana (''Lantana camara'' and ''L. montevidensis'') and Prickly Pear (''Opuntia'' spp.) A range of herbaceous species have also been introduced to these woodlands, either deliberately or accidentally including Rhodes grass and other ''Chloris'' species, Buffel grass (''Cenchrus ciliaris''), Giant rat's tail grass (''Sporobolus pyramidalis'') parthenium (''Parthenium hysteropherus'') and stylos (''Stylosanthes'' spp.) and other legumes. These introductions have the potential to significantly alter the structure and composition of savannas worldwide, and have already done so in many areas through a number of processes including altering the fire regime, increasing grazing pressure, competing with native vegetation and occupying previously vacant ecological niches. Other plant species include: white sage, spotted cactus, cotton seed, rosemary.

Climate change

There exists the possibility that human induced climate change in the form of the greenhouse effect may result in an alteration of the structure and function of savannas. Some authors have suggested that savannas and grasslands may become even more susceptible to woody plant encroachment as a result of greenhouse induced climate change. However, a recent case described a savanna increasing its range at the expense of forest in response to climate variation, and potential exists for similar rapid, dramatic shifts in vegetation distribution as a result of global climate change, particularly at ecotones such as savannas so often represent.

Savanna ecoregions

Savanna ecoregions are of several different types:

Tropical and subtropical savannas are classified with tropical and subtropical grasslands and shrublands as the tropical and subtropical grasslands, savannas, and shrublands biome. The savannas of Africa, including the Serengeti, famous for its wildlife, are typical of this type.

Temperate savannas are mid-latitude savannas with wetter summers and drier winters. They are classified with temperate savannas and shrublands as the temperate grasslands, savannas, and shrublands biome, that for example cover much of the Great Plains of the United States. (See areas such as the Central forest-grasslands transition).

Mediterranean savannas are mid-latitude savannas in Mediterranean climate regions, with mild, rainy winters and hot, dry summers, part of the Mediterranean forests, woodlands, and scrub biome. The oak tree savannas of California, part of the California chaparral and woodlands ecoregion, fall into this category.

Flooded savannas are savannas that are flooded seasonally or year-round. They are classified with flooded savannas as the flooded grasslands and savannas biome, which occurs mostly in the tropics and subtropics.

Montane savannas are high-altitude savannas, located in a few spots around the world's high mountain regions, part of the montane grasslands and shrublands biome. The highland savannas of the Angolan Scarp savanna and woodlands ecoregion are an example.

See also

Cerrado‎

Coastal plain

Coastal prairie

Field

Flood-meadow

Flooded grasslands and savannas

Grassland

Meadow

Oak savanna

Pampas

Pasture

Plain

Prairie

Rangeland

Steppe

Veld

Water-meadow

Wet meadow

References

External links

The Savanna

Category:Grasslands Category:Ecosystems Category:Temperate grasslands, savannas, and shrublands Category:Tropical and subtropical grasslands, savannas, and shrublands

ar:سافانا az:Savannalar be:Саванна be-x-old:Савана bs:Savana bg:Савана ca:Sabana cv:Саванна cs:Savana da:Savanne de:Savanne et:Savann es:Sabana eo:Savano eu:Sabana fa:ساوانا fr:Savane fy:Savanne gl:Sabana ko:사바나 기후 hi:सवाना hr:Savana io:Savano id:Sabana it:Savana he:סוואנה ka:სავანა kk:Саванна sw:Savana la:Savanna lv:Savanna lt:Savana ln:Esóbé hu:Szavanna ml:സവേന my:ဆာဗားနားမြက်ခင်းပြင် nl:Savanne (landschap) ja:サバナ (地理) no:Savanne nn:Savanne oc:Savana pnb:سوانا pl:Sawanna pt:Savana ro:Savană ru:Саванна sq:Savana si:සවානා simple:Savanna sk:Savana sl:Savana sr:Савана sh:Savana fi:Savanni sv:Savann ta:புல்நிலம் tr:Savan uk:Савана vi:Xavan bat-smg:Savana zh:熱帶乾濕季氣候

Tropical and subtropical grasslands, savannas, and shrublands are a grassland terrestrial biome located in semi-arid to semi-humid climate regions of subtropical and tropical latitudes. Grasslands are dominated by grass and other herbaceous plants. Savannas are grasslands with scattered trees. Shrublands are dominated by woody or herbaceous shrubs.

Rainfall in tropical and subtropical grasslands, savannas, and shrublands is between 450 and 1500 millimeters (18 to 60 inches) a year, and can be highly seasonal, with the entire year's rainfall sometimes occurring within a couple of weeks.

Tropical and subtropical grasslands, savannas, and shrublands occur on all continents but Antarctica. They are widespread on Africa, and are also found all throughout South Asia, the northern parts of South America and Australia, and the southern United States.

African Savannas occur between forest or woodland regions and grassland regions. The climate varies, with an average temperature of 27 °C with peaks of 30 °C in April and October, and between 300 and 1500 millimetres of rain per year. Flora includes:

Acacia (Tree)

*Loses leaves in dry season to conserve moisture

*Leafy canopy in rainy season (flattened by winds)

Baobab (Tree)

*Stores water in trunk

*Thick bark to protect it from fires in dry season

*Long tap roots to reach underground moisture

*Few leaves to reduce water loss through transpiration

Grass

*Grow quickly to 3 or 4 meters in clumps

*Shoots die in dry season leaving only roots

Low shrubs

*Drought resistant

*Small

*Thorns not leaves

Tropical and subtropical grasslands, savannas, and shrublands ecoregions

See also

External links

(World Wildlife Fund)

Category:Terrestrial biomes Category:Habitats *

ca:Praderies, sabanes i matollars tropicals i subtropicals eo:Tropikaj kaj subtropikaj herbejoj, savanoj kaj arbedaroj

country	England
fullname	Andrew Nicholas Edwards
living	true
dayofbirth	12
monthofbirth	11
yearofbirth	1978
placeofbirth	Delft, South Holland
countryofbirth	Netherlands
batting	Right-handed
bowling	Right-arm off break
family	Gordon Edwards (father)
club1	Gloucestershire Cricket Board
year1	1999-2000
club2	Herefordshire
year2	1999-2001
deliveries	balls
columns	1
column1	LA
matches1	6
runs1	96
bat avg1	24.00
100s/50s1	–/–
top score1	38
deliveries1	216
wickets1	5
bowl avg1	25.80
fivefor1	–
tenfor1	–
best bowling1	3/38
catches/stumpings1	2/–
date	9 November
year	2010
source	http://www.cricinfo.com/ci/content/player/12495.html Cricinfo }}

Andrew Nicholas Edwards (born 12 November 1978) is a former English cricketer. Edwards was a right-handed batsman who bowled right-arm off break. He was born in Delft, South Holland in the Netherlands.

Edwards made his debut in List A cricket for the Gloucestershire Cricket Board against the Yorkshire Cricket Board in the 1999 NatWest Trophy. From 1999 to 2001, he represented the Board in 2 further List A matches. These came against the Nottinghamshire Cricket Board and the Yorkshire Cricket Board, both in the 2000 NatWest Trophy.

In 1999, Edwards also made his debut for Herefordshire in the Minor Counties Championship against Devon. In 2001, he played 3 further Championship matches for the county, the last of which came against Berkshire. In 2001, he played a single MCCA Knockout Trophy match for Herefordshire against the Warwickshire Cricket Board. Edwards also represented the county in List A cricket, making his debut for the county in that format against the Gloucestershire Cricket Board in the 2001 Cheltenham & Gloucester Trophy. He played 2 further matches in that seasons competition against Middlesex, who they famously defeated by 3 wickets, and Worcestershire.

In his career total of 6 List A matches, he scored 96 runs at a batting average of 24.00, with a high score of 38. In the field he took 2 catches. With the ball he took 5 wickets at a bowling average of 25.80, with best figures of 3/38.

Father

His father, Gordon, played first-class and List A cricket for Nottinghamshire in 1973.

References

External links

Andrew Edwards at Cricinfo

Andrew Edwards at CricketArchive

Category:1978 births Category:Living people Category:People from Delft Category:English cricketers Category:Herefordshire cricketers Category:Gloucestershire Cricket Board cricketers