There isn't a universally accepted "unchanging final stage" for an ecosystem. The concept you're describing is called climax community, which is a theoretical, stable, mature stage of ecological succession.

Here's why it's not entirely accurate to call it "unchanging":

* Dynamic Equilibrium: Ecosystems are constantly in a state of flux, influenced by various factors like climate change, disturbances, and species interactions. Even climax communities experience change, albeit at a slower pace.

* Succession is not Linear: Succession is a complex process, and ecosystems don't always follow a predictable linear path. Different environmental factors can lead to different climax communities in the same region.

* Disturbances are Essential: Natural disturbances like fires, floods, or windstorms are a necessary part of ecosystem dynamics. These disturbances can reset succession and prevent a single climax community from persisting indefinitely.

Instead of an "unchanging final stage," it's more accurate to think of ecosystems as constantly evolving and adapting to their environment. The concept of climax communities is a useful framework for understanding ecosystem development, but it shouldn't be interpreted as a fixed endpoint.