Final answer:
The community of lichens, mosses, and grasses on the volcanic rock field will change over time due to ecological succession. Pioneer species like lichens help break down the rocks and create soil, allowing other plants to establish and eventually form a mature community.
Step-by-step explanation:
The community of lichens, mosses, and grasses covering the field of volcanic rocks will change over many years due to the process of ecological succession. Ecological succession is the gradual and predictable change in the composition of a community over time. In this case, lichens and other pioneer species are the first to colonize the bare rocks. They help break down the rocks and create soil, making it possible for other plants like grasses to grow. As the grasses establish themselves, they change the environment and pave the way for the growth of larger plants, eventually leading to a mature and diverse community.