Lichen growing on barren rock in the tundra is an example of primary succession.

Here's why:

* Primary Succession: This occurs in environments where there is no pre-existing soil. The first organisms to colonize these areas are called pioneer species.

* Secondary Succession: This occurs in areas where the existing community has been disrupted, but the soil remains intact.

In the case of the tundra, the barren rock provides no soil for existing plants to grow in. Lichen, a pioneer species, can break down the rock, creating the first layer of soil. This allows for other plants to eventually colonize the area, leading to a more complex ecosystem.

Let me know if you have any other questions!