Explanation:

Ecological succession typically begins when the existing biological community has been cleared away by human activity or natural disturbance such as a fire or severe storm. The population of trees that once lived in this area can’t grow back

because the fire has changed the ground composition. Without tree roots to act as anchors, rain washes away the soil and the ground becomes rocky and barren. This rocky ground, however, proves ideal to lichens, the pioneer population. Mosses and herbs are well suited to living in the shallow soil environment created by the lichen, and they replace the lichen as the dominant population. Grasses intercept most of the rainwater before it reaches the roots of the shrubs. Because the grasses limit the supply of water to the shrub seedlings, they maintain the integrity of the ecosystem as a grass ecosystem.