Here's why:

* Permafrost: Permafrost is a layer of soil that remains frozen for at least two consecutive years. This permanently frozen ground is a defining feature of the tundra biome.

* Tundra Biome: The tundra biome is characterized by extremely cold temperatures, low precipitation, and a short growing season. The permafrost layer prevents deep-rooted plants from growing, leading to the unique vegetation of the tundra, such as mosses, lichens, and low-lying shrubs.

Let me know if you have any other questions!