Final answer:
Grasses were able to grow in the area because they are pioneer species that are well-suited to grow in thin, poor soil.
Step-by-step explanation:
The grasses were able to grow in the area because they are pioneer species that are well-suited to grow in thin, poor soil. After a wildfire, the vegetation is removed, leaving behind bare soil. The first organisms to grow in this environment are lichens and mosses, which help to break down the rock and form soil. As the soil improves, grasses are able to establish and compete for resources. Over time, shrubs and trees will emerge, leading to the development of a stable climax community.