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savanna
A savanna or savannah is a grassland 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.〔Anderson, Roger A., Fralish, James S. and Baskin, Jerry M. editors.1999. Savannas, Barrens, and Rock Outcrop Plant Communities of North America. Cambridge University Press.〕〔McPherson, G. R. (1997). Ecology and management of North American Savannas. Tucson, AZ: University of Arizona Press.〕
Savannas maintain an open canopy despite a high tree density.〔Alexandro Solórzano, Jeanine Maria Felfili 2008”Comparative analysis of the international terminaoolgy for cerrado” IX Symposio Nacional Cerrado 13 a 17 de outubro de 2008 Parlamundi Barsilia, DF〕 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.〔Manoel Cláudio da Silva Jánior, Christopher William Fagg, Maria Cristina Felfili, Paulo Ernane Nogueira, Alba Valéria Rezende, and Jeanine Maria Felfili 2006 “Chapter 4. Phytogeography of Cerrado Sensu Stricto and Land System Zoning in Central Brazil” in “Neotropical Savannas and Seasonally Dry Forests: Plant Diversity, Biogeography, and Conservation” R. Toby Pennington, James A. Ratter (eds) 2006 CRC Press〕〔Abdullahi Jibrin 2013 “A Study of Variation in Physiognomic Characteristics of Guinea Savanna Vegetation” Environment and Natural Resources Research 3:2〕〔Erika L. Geiger, Sybil G. Gotsch, Gabriel Damasco, M. Haridasan, Augusto C. Franco & William A. Hoffmann 2011 “Distinct roles of savanna and forest tree species in regeneration under fire suppression in a Brazilian savanna” Journal of Vegetation Science 22〕〔Scholz, Fabian G.; Bucci, Sandra J.; Goldstein, Guillermo; Meinzer, Frederick C.; Franco, Augusto C.; Salazar, Ana. 2008 “Plant- and stand-level variation in biophysical and physiological traits along tree density gradients in the Cerrado”, Brazilian Journal of Plant Physiology〕 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 800–3300 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 the same region.〔Tait, L 2010, Structure and dynamics of grazed woodlands in North-eastern Australia, Master of Applied Science Thesis, Central Queensland University, Faculty of Science, Engineering and Health, Rockhampton.〕
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. Savanna covers approximately 20% of the Earth's land area.
==Etymology==
The word originally entered English in 1555〔''Oxford English Dictionary'', "savannah", ''n.'' Oxford University Press (Oxford), 2012.〕 as the Latin ''Zauana'', 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, but this is usually placed in present-day Madugandí or at points on the nearby Guna Yala coast opposite Ustupo〔Bancroft (1882), 〕 or on Point Mosquitos.〔Bancroft (1882), 〕 These areas are now either given over to modern cropland or jungle.〔NASA. "(Land Cover Classification )" from ''Earth Observatory. The Image Composite Explorer. Exercise 4: Vegetation Vital Signs''. Accessed 1 August 2014.〕
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