Tropical savanna is the predominant vegetation type across the northern quarter of Australia where rainfall is above 600 mm yr_1, an area of million km2 (Figures 1 a, 1b, and 2). These savannas are open woodlands and open forests, with tree cover declining as rainfall decreases with distance from the northern coast. The overstorey flora is typically dominated by Eucalyptus spp., particularly Eucalyptus tetrodonta, E. dichromophloia, and E. miniata. Melaleuca viridiflora, M. nervosa, and E. pruinosa assemblages occur in the drier regions of this biome where annual rainfall <1000 mmyr-1. The ground layer is dominated by annual and perennial grasses from the Sarga, Heteropogon, and Schizachrium genera. A variety of other tall grasses (>1m height) dominate the ground layer of the monsoonal savannas, which extend from Western Australia to the Cape York Peninsula in Queensland. Heteropogon contortus (black speargrass) dominates the tropical savanna unders-tory in eastern Queensland, with Themeda triandra, Aristida, Bothriochloa, and Chrysopogon bladhii becoming more dominant as rainfall declines. Acacia-dominated savanna communities include extensive areas of brigalow (A. harpo-phylla), lancewood (A. shirleyi), and gidgee (A. cambegei and A. georginae).
The neotropical savannas of South America cover more than 2 million km2. The Brazilian cerrado and the Colombian and Venezuelan llanos are a continuous formation, interrupted by narrow gallery forests. The cerradao includes a range of vegetation formations from the pure or almost pure grassland of camp limpo, to open woodland with scattered tree cover of campo cerrado. These savanna can grade into denser woodland or open forests, the cerradao, where tree cover is greater than 50%. The dominant grasses are Andropogon, Aristida, Paspalum, and Trachypogon. The Orinoco llanos comprise grasslands or grasslands with scattered trees which are typically <8 m tall. Common trees include Byrsonima spp. Curatella americana, Bowdichia virgioides, and grasses include Trachypogon and Andropogon. Hyper-seasonally flooded savannas and esteros (savanna wetland) occur in Brazil and Bolivia. Other savanna types, such as savanna parkland and mixed woodland, occur through tropical America.
The African savannas occur across a range of soil types within a rainfall range of 200-1800 mm. One of the most extensive savanna areas is the miombo which covers about 2.7 million km2 across central and southern Africa. The miombo is characterized by a discontinuous canopy of 10-12 m tall deciduous species of Brachystegia, Isoberlinia, and Julbernardia, with an herbaceous layer of tall grasses including mainly Andropogon species. In southern Africa, fine-leaved savannas, dominated by Acacia species, occur over fertile soils in low-lying, semiarid (250-650 mm yr-1) areas. Broadleaved savannas, including Burkea africana,
Combretum spp., and Brachystegia, occur on weathered, infertile soils. The northern Sudanian savannas have scattered deciduous trees, typically Isoberlinia doka, over xerophytic grasslands. These are bordered on the north by the drier Sahelian savannas and on the south by the wetter Guineatype savannas. The arid and semiarid east African savannas are grasslands dominated by Aristida spp. and Brachiara spp., with scattered shrubs or trees (including Acacia, Grewia, and Commiphora), for example, the Serengeti.
Savannas occur throughout Asia, although many of these are derived from human disturbance. Savanna is fairly extensive in the Indian subcontinent, although tree clearing has increased their extent, and many areas have been converted to agriculture. The most significant and widespread savanna type in Southeast Asia is the dry dipterocarp forest, which occurs in Vietnam, Laos, Cambodia, Thailand, Burma, and a small area in India. The region receives 1000-1500 mm rain per year and is dominated by the deciduous Dipterocarpus species, which can grow to 20 m, over a dense grass and herb layer including Imperata cylindrical, Apluda mutica, and Arundinaria spp. (pygmy bamboo).
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