The type of change that was seen in the ecosystems that were affected by the 1988 fires in Yellowstone Park is SECONDARY SUCCESSION.
Succession is the process by which the ecological structure of a community changes over time. There are two basic types of ecological succession, these are primary and secondary succession. A succession is said to be secondary, if the succession process is started by an occurrence which reduces an already established ecosystem to a smaller population of species.
In the question given above, the type of succession that occurred was secondary succession, this is because the wildfires destroyed some of the animals and plants that are found at Yellowstone Park thus reducing the number of plants and animal species found in that ecosystem.