APJ Abdul Kalam Essay Example for Free

APJ Abdul Kalam EssayIntroductionA savannahhh, or savannah, is a grass footing ecosystem characterized by the shoetrees being sufficiently 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 grasses.123 The oak savanna is a crude type of savanna in the Northern Hemisphere. Some classification systemswhich? also recognize a grassland savanna from which trees be absent.4 This article deals only with savanna chthonian the common definition of a grassy woodland with a significant cedarn kit and caboodle component. It is often believed that savannas feature widely spaced, baffled trees. However, in more savannas, tree densities are higher and trees are more regularly spaced than in forest. savannahs are also characterized by seasonal water availability, with the majority of rain confined to one season. Savannas are associated with several(prenominal) t ypes of biomes. Savannas are frequently in a transitional zone between forest and desert or grassland. Savanna covers approximately 20% of the Earths land area.EtymologyCerrado savanna, Brazil.Although the term savanna is believed to have accreditedly come from an Arawak word describing land which is without trees but with overmuch grass both lofty or short (Oviedo y Valdes, 1535), by the late 1800s it was make use ofd 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 telephone exchange Plateau.DistributionMany grassy landscapes and mixed communities of trees, shrubs, and grasses were described as savanna before the pump of the 19th century, when the conc ept of a tropical savanna climate became established. The Kppen climate classification system was strongly influenced by outlets of temperature and precipitation upon tree growth, and his oversimplified assumptions subjected in a tropical savanna classification concept which resulted in it being considered as a climatic climax formation. The common usage importation to describe vegetation now conflicts with a simplified yet wide riddle climatic concept meaning.The divergence has sometimes caused areas such(prenominal) as extensive savannas trades union and south of the Congo and Amazon Rivers to be excluded from mapped savanna categories.5 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 510% and upper limits surf as 2580% of an area.6 Two factors common to all savanna environments are rain fall variations from year to year, and change season wildfires. In the Americas, e.g. in Belize, Central America, savanna vegetation is similar from Mexico to South America and to the Caribbean.ThreatsChanges in fire managementSavannas 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.8 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,9 and savannas in India are a result of human fire use.10 The maquis shrub savannas of the Mediterranean region were likewise created and maintained by anthropogenic fire.11Prescribed burn Wisconsin bur oak savannaThese fires are usually confined to the herbaceou s layer and do little long term damage to mature trees. However, these fires either kill or jamtree 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 vegetation12 and may have maintained and modified savanna flora.39 It has been suggested by galore(postnominal) authors1213 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 divagate of numerous woodland species.912 It has been suggested by many another(prenominal) authors1314 that with the remotion or transformation of traditional burning regimes many savannas are being replaced by forest and shrub thickets with little herbaceous layer.The consumption of pasturage by introduced grazers in savanna woodlands has l ed to a reduction in the amount of fuel available for burning and resulted in fewer and cooler fires.15 The debut of exotic pasture legumes has also led to a reduction in the need to burn to produce a flush of green growth because legumes refrain high nutrient levels throughout the year, and because fires can have a negative impact on legume populations which causes a reluctance to burn.16Grazing and browsing animalsoak tree savanna, United StatesThe closed forest types such as broadleaf forests and rainforests are usually not grazed owing to the closed structure precluding grass growth, and indeed offering little opportunity for eat.17 In contrast the open structure of savannas allows the growth of a herbaceous layer and are commonly used for grazing domestic livestock.18 As a result much of the worlds savannas have undergone change as a result of grazing by sheep, goats and cattle, ranging from changes in pasture firearm to woody weed encroachment.19 The removal of grass by g razing affects the woody plant component of woodland systems in two major ways. Grasses compete with woody plants for water in the top dirty word and removal by grazing reduces this competitive effect, potentially boosting tree growth.In addition to this effect, the removal of fuel reduces both the rapture and the frequency of fires whichmay control woody plant species.21 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.22 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.12 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.).15 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.23 The effects of overstocking are often worst on soils of low fertility and in low rainfall areas below calciferol mm, as most soil nutrients in these areas tend to be concentrated in the surface so any movement of soils can lead to utter(a) 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 clearingLarge areas of Australian and South American savannas have been cleared of trees, and this clearing is continuing today. For example until rec ently 480,000 ha of savanna were cleared annually in Australia alone primarily to improve pasture production.12 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. unclutter 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.24Since stock carrying capacity is strongly correlatedwith herbage yield, there can be major financial benefits from the removal of trees,25 such as assisting with grazing management regions of dense tree and shrub cover harbors predators, leading to increased stock losses, for example,26 wh ile woody plant cover hinders mustering in both sheep and cattle areas.27 A frame 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.28 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 presentment 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 utilized 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(prenominal) fire as most Queensland savannas are, there is a similar response to that after fire.29 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 to a fault 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 speciesAcacia savanna, Taita Hills Wildlife Sanctuary, Kenya.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 tree (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 rats dark grass (Sporobolus pyramidalis)parthenium (Parthenium hysterophorus) 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.2930 Other plant species acknowledge white sage, spotted cactus, cotton seed, rosemary.Climate changeThere 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 authors31 have suggested that savannas and grasslands may become even more su sceptible 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.32Savanna ecoregionsMediterranean savanna in Alentejo region, Portugal.Savanna ecoregions are of several different typesTropical 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. The Brazilian savanna (Cerrado) is also included in this category, known for its exotic and varied flora. Temperate savannas are mid-latitude savannas with wetter summers and drier winters. They are clas sified with clement 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 theMediterranean 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 spot around the worlds high mountain regions, part of the montane grasslands and shrublands biome. The lowland savannas of the Angolan Scarp savanna and woodlands ecoregion are an example.