3. How can overgrazing reverse the succession of a grassland ecosystem? -

Over grazing can easily reverse the grassland succession.

Explanation:

An ecological succession is defined as the process of nature undertaking a barren land that was previously not suitable for any life. This process requires time. Here the lichens and fungi first breaks the rocks and produces some humus after death that can be used by other plants whose seeds are brought by wind or birds and they germinate to form the new ecosystem.

Now overgrazing kills the newly formed plants. And the humus content also gets reduced because of the unavailability of the organic matter over the place. So overgrazing will kill these plants and again reverse back the succession to previous forms.