ABSTRACT
India, and South East Asia (Fig. 1). African tropical savannas are scattered across a wide variety of soil conditions with annual rainfall ranging from 200 to 1800 mm; they form a semi-circle around the western central rainforest, bordered by deserts to the north and south.[7-9] In African savanna, fi ne-leaved woody vegetation mainly dominated by Acacia species occurs on nutrient-rich soils in low-lying semi-arid areas in Botswana, South Africa, and Namibia. On the contrary, broad-leaved savanna species (e.g., Combretum spp., Lonchocarpus nelsii, and Terminalia spp.) can be seen in the sub-humid interior plateau on infertile and highly weathered soils.[10] The Guinea-type savanna woodlands in humid climates replace moist semi-deciduous vegetation and form a transition to evergreen moist forests, whereas northern Sudan-type savannas with scattered Acacia trees form a transition with Sahara desert vegetation.[10,11] The Miombo woodland savanna covers an additional 2.7 million km2 area across central and southern Africa and is characterized by the presence of deciduous species of Brachystegia, Isoberlinia, and Fulbbernardia, forming a discontinuous canopy with an average height of 10 m.[12] In South America, tropical savanna comprises the biologically rich Brazilian Cerrado and the Colombian and Venezuelan Llanos, together covering over 2 million km2 in area. Rich in fauna, the Cerrado bioregion contains a gradient from completely open savannas to closed canopy forest along environmental shifts in rainfall, topography, and human infl uence. Besides producing most of the beef cattle of Brazil, with the implementation of soil improvement techniques and irrigation, Cerrado areas are now also important producers of soy and grains.[3,13] The Australian tropical savanna is contiguous with little
topographic variation and covers about 12% of the total tropical savanna area.[14] In northern Australia, savanna open Eucalyptus spp. woodlands is the dominant land cover type. The woody canopy cover decreases from northern Australia toward the continent’s interior, following the rainfall gradient.[15,16] In general, the woody vegetation in Australian tropical savannas has predominantly evergreen tree species that is different from African tropical savannas with mostly deciduous tree species.[17] Also, compared to the tropical savannas in other continents, Australian tropical savannas have lower population density and thus are ecologically less modifi ed. However, due to increasing economic activities, particularly mining and agriculture, their future remains uncertain.[15,18]
● Temperate grasslands are known as prairies in North America (covering 5 million km2), steppes in Eurasia, pampas in Argentina and Uruguay in South America, and the veld region in South Africa. These mid-latitude grasslands experience wet summers and dry winters; the climate can range from temperate to semi-arid to sub-humid. Compared to tropical savannas, temperate grasslands have lower biodiversity. Typical kinds of grasses include Bouteloua dactyloides (buffalo grass), Lolium (ryegrass), Avena (wild oats), and Nassella pulchra (purple needlegrass), which also are all part of the diet of herbivorous animals. Grass height depends on the amount of rainfall received from late spring to early summer, which ranges in total between 450 and 700 mm.[9] Often lightning from thunderstorms can ignite large grass fi res in temperate grasslands, which keeps trees from overshadowing the grasses and acts to maximize biodiversity by creating landscape heterogeneity. Soils are deep and dark with fertile upper layers.
