A lone tree in Zambia

Standing all alone in the grass.

In contrast to all the other trees that grow thickly together.

or even more densely packed together.

These are examples of the perpetual struggle between grassland and bush in the African savanna's. Bush crouds out the grass and prevents it from growing in its shade. Where grass is thick wild fires wipe out small trees and only the largest ones survive.

So when grass is aloud to accumulate the fires will be hotter and eliminate all the smaller trees, then only single scattered large trees will remain. When fires are scarce or the grass is overgrazed the trees will begin to reclaim their territory and so the pendulum sways over the centuries between grassland and savanna woodland.