The phrase you provided is incomplete. It seems like you're describing the habitat of a fern. To complete the sentence and make it meaningful, we need more information.

Here are a few possibilities:

* The moist riverbank where a fern lives is a haven for other plants and animals. This emphasizes the biodiversity of the area.

* The moist riverbank where a fern lives is a delicate ecosystem. This highlights the importance of maintaining its fragile balance.

* The moist riverbank where a fern lives is a place of constant change. This emphasizes the dynamic nature of the environment.

To get a more accurate answer, please provide more context or the full sentence.