At a continental scale vegetation can be divided up into biomes: groups of plants that form an environment of particular structure that is adapted for a particular climate. The unseasonal warm wet regions have closed canopy tropical rainforest, whereas tropical regions with seasonal rainfall have woodlands, savannas, shrublands or desert (depending on how much rain, for how long and at what time of the year). Add into this the fire dynamics of a region and you can further modify the structure of a biome. In turn, which biome is where has feedbacks on climate, the water cycle and the carbon cycle. So what could explain a region with a climate and fire regime suitable for closed canopy forest, but a natural (no human influence) biome of open woodland and savanna? Well Hempson et al. have demonstrated that for Africa it is the presence of large herbivores. In their paper published in Science, they demonstrate that for certain areas of Africa the natural vegetation is under the control of large herbivorous mammals.

Travel back in time 100,000 years and large herbivorous mammals are far more numerous, diverse and widely spread on Earth. Many of these are not extinct and the possibility exists that our natural world is still responding to the loss of large mammalian herbivores, whilst Anthropogenic climate change threatens to add further chaos to natural cycles.

See also:

Original paper:

Perspective from J.L. Gill: