Savanna

Savannas maintain an open canopy despite a high tree density.^[5] 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.^[6][7][8][9] 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,^[6][8][9] 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,^[7] while Eastern Australian sclerophyll forests have average tree densities of approximately 100 per hectare, comparable to savannas in the same region.^[10]


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 they're mostly a transition between desert to forest.^[11] Savanna covers approximately 20% of the Earth's land area.^[12] Unlike the prairies in North America and steppes in Eurasia, which would feature cold winters, savannahs are mostly located in areas having warm to hot climates, such as those in Africa, Australia, Thailand, South America and India.^[13]

Etymology

The word derives from the Spanish sabana, which is itself a loanword from Taíno, which means "treeless grassland" in the West Indies.^[14][15] The letter b in Spanish, when positioned in the middle of a word, is pronounced almost like an English v; hence the change of grapheme when transcribed into English.^[16]


The word originally entered English as the Zauana in a description of the ilands of the kinges of Spayne from 1555.^[17][19] 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, the court of the cacique Carlos in present-day Panama. The accounts are inexact,^[21] but this is usually placed in present-day Madugandí^[22] or at points on the nearby Guna Yala coast opposite Ustupo^[23] or on Point Mosquitos.^[24] These areas are now either given over to modern cropland or jungle.^[25]

Ecology

The savannas of tropical America comprises broadleaved trees such as Curatella, Byrsonima, and Bowdichia, with grasses such as Leersia and Paspalum. Bean relative Prosopis is common in the Argentinian savannahs. In 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 consist of Anogeissus, Combretum, and Strychnos. Indian savannas are mostly cleared, but the reserved ones feature Acacia, Mimosa, and Zizyphus over a grass cover comprising Sehima and Dichanthium. The Australian savannah is abundant with sclerophyllous evergreen vegetation, which include the eucalyptus, and as well as Acacia, Bauhinia, Pandanus with grasses such as Heteropogon and kangaroo grass (Themeda).^[4]


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 the Australian savannah, 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.^[4]