Misplaced Pages

#441558

50-421: It is located in the state of Pará, Brazil. It presents muddy and turbid waters, rich in sediments originating from its source rivers. Runs for approximately 64 kilometres (40 mi), around the west and south of the island of Marajó . Belém , the state capital of Pará , is located near the south bank of the river. Previously academic research has come to consider this watercourse as a distributary channel of

100-438: 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

150-491: 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. A number of exotic plants species have been introduced to savannas around

200-1013: A light canopy, tree savanna with scattered trees and shrubs, shrub savanna with distributed shrubs, and grass savanna where trees and shrubs are mostly nonexistent. Savannas maintain an open canopy despite a high tree density. 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 forests. The South American savanna types cerrado sensu stricto and cerrado dense typically have densities of trees similar to or higher than that found in South American tropical forests, with savanna ranging from 800 to 3300 trees per hectare (trees/ha) and adjacent forests with 800–2000 trees/ha. Similarly Guinean savanna has 129 trees/ha, compared to 103 for riparian forest , while Eastern Australian sclerophyll forests have average tree densities of approximately 100 per hectare , comparable to savannas in

250-402: 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

300-444: 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. The closed forest 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

350-469: 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

400-586: A river in Pará , Brazil is a stub . You can help Misplaced Pages by expanding it . Maraj%C3%B3 Marajó ( Portuguese pronunciation: [maɾaˈʒɔ] ) is a large coastal island in the state of Pará , Brazil. It is the main and largest of the islands in the Marajó Archipelago . Marajó Island is separated from the mainland by Marajó Bay , Pará River , smaller rivers (especially Macacos and Tajapuru), Companhia River, Jacaré Grande River, Vieira Grande Bay and

450-455: A simplified yet widespread climatic concept. 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. In different parts of North America, the word "savanna" has been used interchangeably with " barrens ", " prairie ", " glade ", "grassland" and " oak opening ". Different authors have defined

500-423: Is contained in the 59,985 square kilometres (23,160 sq mi) Marajó Archipelago Environmental Protection Area , a sustainable-use conservation unit established in 1989 to protect the environment of the region. Large parts of the islands are flooded during the rainy season because of higher water levels of the rivers along the coast and heavy rainfall in the interior. Marajó is almost entirely flat. During

550-477: Is not prominent but that rivers in savanna landscapes erode more by lateral migration . Flooding and associated sheet wash have been proposed as dominant erosion processes in savanna plains. The savannas of tropical America comprise broadleaved trees such as Curatella , Byrsonima , and Bowdichia , with grasses such as Leersia and Paspalum . Bean relative Prosopis is common in the Argentinian savannas. In

SECTION 10

#1733085453442

600-473: Is possible for there to be multiple stable biomes. The annual rainfall ranges from 500 mm (19.69 in) to 1,270 mm (50.00 in) per year, with the precipitation being more common in six or eight months of the year, followed by a period of drought. Savannas may at times be classified as forests. In climatic geomorphology it has been noted that many savannas occur in areas of pediplains and inselbergs . It has been posited that river incision

650-419: Is vague and therefore the two can be combined into a single biome as both woodlands and savannas feature open-canopied trees with crowns not usually interlinking (mostly forming 25-60% cover). Over many large tropical areas, the dominant biome (forest, savanna or grassland) can not be predicted only by the climate, as historical events plays also a key role, for example, fire activity. In some areas, indeed, it

700-526: The Atlantic Ocean . From approximately 400 BC to 1600 AD, Marajó was the site of an advanced Pre-Columbian society called the Marajoara culture , which may have numbered more than 100,000 people at its peak. Today, the island is known for its large water buffalo population, as well as the pororoca tidal bore periodically exhibited by high tides overcoming the usual complex hydrodynamic interactions in

750-455: The Mediterranean region were likewise created and maintained by anthropogenic fire. Intentional controlled burns typically create fires confined to the herbaceous layer that do little long term damage to mature trees. This prevents more catastrophic wildfires that could do much more damage. However, these fires either kill or suppress tree seedlings, thus preventing the establishment of

800-712: The Pará River , some smaller rivers (especially Macacos and Tajapuru), the Companhia River, the Jacaré Grande River , Vieira Grande Bay, and the Atlantic Ocean . The island sits almost directly on the Equator . Together with smaller neighboring islands that are separated from Marajó by rivers, they form the Marajó Archipelago, with an aggregate area of 49,602 square kilometres (19,151 sq mi). The archipelago

850-476: 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

900-717: The prairies in North America and steppes in Eurasia , which feature cold winters, savannas are mostly located in areas having warm to hot climates, such as in Africa, Australia, Thailand, South America and India. The word derives from the Spanish sabana , which is itself a loanword from Taíno , which means "treeless grassland" in the West Indies . The letter b in Spanish, when positioned in

950-561: The 1980s. According to Roosevelt, the Marajoara culture developed independently within the Amazon and featured both intensive subsistence agriculture and major public works. Roosevelt estimated that Marajó may have had a population of more than 100,000 people at its peak. The population lived in homes with tamped earth floors, organized themselves into matrilineal clans , and divided tasks by sex, age, and skill level. The arrival of Europeans in

1000-565: The Amazon River. However, this statement is currently considered unlikely, since recent studies have shown the small contribution of the waters of the Amazon River to the formation of the Pará River, with a greater contribution from the Tocantins River. 1°43′43″S 49°10′34″W  /  1.72871°S 49.1762°W  / -1.72871; -49.1762 This article related to

1050-544: The Australian savanna, mammals in the family Macropodidae predominate, such as kangaroos and wallabies, though cattle, horses, camels, donkeys and the Asian water buffalo , among others, have been introduced by humans. It is estimated that less than three percent of savanna ecosystems can be classified as highly intact. Reasons for savanna degradation are manifold, as outlined below. Savannas are subject to regular wildfires and

SECTION 20

#1733085453442

1100-499: The East African savannas, Acacia , Combretum , baobabs , Borassus , and Euphorbia are a common vegetation genera. Drier savannas there feature spiny shrubs and grasses, such as Andropogon , Hyparrhenia , and Themeda . Wetter savannas include Brachystegia trees and Pennisetum purpureum , and elephant grass type. West African savanna trees include Anogeissus , Combretum , and Strychnos . Indian savannas are mostly cleared, but

1150-532: The Marajoara culture had been founded by emigrants from the Andes and that the society steadily declined until its final collapse at approximately 1400 AD, due to the Marajó's poor soil fertility and other environmental factors. Megger's hypotheses subsequently became associated with environmental determinism . Her theory has since been rejected, however, by the archaeologist Anna Curtenius Roosevelt , who re-excavated Marajó in

1200-513: The Northern Territory, Australia savanna, and 480,000 ha of savanna were being cleared annually in Queensland in the 2000s, 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

1250-427: The bore. The eastern side of the island is dominated by savanna vegetation. There are large fazendas with animal husbandry. This is also the location of Lake Arari, which has an area of 400 square kilometres (150 sq mi), but shrinks by 80% during the dry season. There are large herds of domesticated water buffalo , which are technically invasive to the island; they now number about 450,000, higher than

1300-415: The court of the cacique Carlos in present-day Panama . The accounts are inexact, but this is usually placed in present-day Madugandí or at points on the nearby Guna Yala coast opposite Ustupo or on Point Mosquitos . These areas are now either given over to modern cropland or jungle . Many grassy landscapes and mixed communities of trees, shrubs, and grasses were described as savanna before

1350-555: The ecosystem appears to be the result of human use of fire. For example, Native Americans created the Pre-Columbian woodlands of North America by periodically burning where fire-resistant plants were the dominant species. 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

1400-467: The establishment, growth and survival of plant species and in turn can lead to a change in woodland structure and composition. That being said, impact of grazing animals can be reduced. Looking at Elephant impact on Savannas, the overall impact is reduced in the presence of rainfall and fences. Large areas of Australian and South American savannas have been cleared of trees, and this clearing continues today. For example, land clearing and fracking threaten

1450-483: 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

1500-619: The illness. The island is also the location of the Roman Catholic Territorial Prelature of Marajó . Savanna A savanna or savannah is a mixed woodland - grassland (i.e. grassy woodland) biome and ecosystem characterised by the trees 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. Four savanna forms exist; savanna woodland where trees and shrubs form

1550-402: The island via its ferry link to Belém . The island is shared by 16 municipalities of three microregions: The island was the site of an advanced pre-Columbian society, the Marajoara culture , which existed from approximately 400 BC to 1600 AD. The island has been a center of archaeological exploration and scholarship since the nineteenth century. Scholars from the 1980s forward have divided

Pará River - Misplaced Pages Continue

1600-459: The island's human population. The western side of the island is characterized by várzea forests and small farms. Lumber and açaí palm are produced there. The island is in the Marajó várzea ecoregion, an area of seasonally and tidally flooded várzea forest . To the north of the large savanna area are palm swamps , mainly with Buriti Palm ( Mauritia flexuosa ) and Euterpe oleracea . During

1650-554: The lower limits of savanna tree coverage as 5–10% and upper limits range as 25–80% of an area. Two factors common to all savanna environments are rainfall variations from year to year, and dry season wildfires . In the Americas , e.g. in Belize , Central America , savanna vegetation is similar from Mexico to South America and to the Caribbean . The distinction between woodland and savanna

1700-461: The middle of a word, is pronounced almost like an English v; hence the change of grapheme when transcribed into English. The word originally entered English as the Zauana in a description of the ilands of the kinges of Spayne from 1555. This was equivalent in the orthography of the times to zavana (see history of V ). Peter Martyr reported it as the local name for the plain around Comagre,

1750-425: 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 oversimplified assumptions resulted in a tropical savanna classification concept which considered it as a "climatic climax" formation. The common usage to describe vegetation now conflicts with

1800-469: The open structure of savannas allows the growth of a herbaceous layer and is 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 plant 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

1850-438: 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. Human induced climate change resulting from

1900-691: The pre-Columbian period into the Ananatuba phase (c. 1100 – c. 200 BC), the Mangueiras phase (c. 1000 BC – c. 100 AD), the Formiga phase (c. 100-400 AD), the Marajoará phase (c. 400-1200 AD), and the Aruã phase (1200-1500 AD). Since the 1990s, there has been debate over the origins and sophistication of Marajó's pre-Columbian society. Based on fieldwork in the 1940s and 1950s, the archaeologist Betty Meggers initially argued that

1950-442: The rainy season, much of the island becomes flooded as a large lake. There are 20 large rivers on the island. Because of the changing water levels and regular seasonal flooding, many settlements are built on stilts ( Palafitas ). The island is known for the pororoca , a tidal bore phenomenon in the river that creates large waves reaching 4 m (13 ft) in height. It is a tourist destination , especially for surfing of

2000-429: The rainy season, the swamps are flooded one meter high. Little is known about the ecology of these swamps. The most important towns are in the southeastern portion of the island: Soure , Salvaterra , and the largest city, Breves . They feature a basic touristic infrastructure and are popular because of the generous, lightly populated beaches. The city of Soure, on the island's Atlantic coast, serves as an entry point to

2050-431: The removal of trees, such as assisting with grazing management: regions of dense tree and shrub cover harbors predators, leading to increased stock losses, for example, 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

Pará River - Misplaced Pages Continue

2100-580: The reserved ones feature Acacia, Mimosa , and Zizyphus over a grass cover comprising Sehima and Dichanthium . The Australian savanna is abundant with sclerophyllous evergreen vegetation, which include the eucalyptus , as well as Acacia, Bauhinia , Pandanus with grasses such as Heteropogon and kangaroo grass (Themeda). Animals in the African savanna generally include the giraffe, elephant, buffalo, zebra, gnu, hippopotamus, rhinoceros, and antelope, where they rely on grass and/or tree foliage to survive. In

2150-449: The same region. Savannas are also characterised by seasonal water availability, with the majority of rainfall confined to one season. They are associated with several types of biomes , and are frequently in a transitional zone between forest and desert or grassland , though mostly a transition between desert to forest. Savanna covers approximately 20% of the Earth's land area. Unlike

2200-460: The sixteenth century was catastrophic to the indigenous population of the island; 90% died due to high mortality from Eurasian infectious diseases ; they lacked immunity against these diseases that had become endemic in Eurasian cities. In contrast, however, during the 1918–1919 pandemic worldwide of Spanish influenza , Marajó was the only major populated area not to have any documented cases of

2250-515: 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

2300-606: 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 species). 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

2350-519: 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

2400-469: The surrounding rivers. It is the second-largest island in South America , and the 35th largest island in the world . With a land area of 40,100 square kilometres (15,500 sq mi) Marajó is comparable in size to Switzerland . Its maximum span is 295 kilometres (183 mi) long and 200 kilometres (120 mi) in perpendicular width. Marajó Island is separated from the mainland by Marajó Bay ,

2450-463: 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

2500-665: 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 hysterophorus ) and stylos ( Stylosanthes spp.) and other legumes . These introductions have

#441558