Here's why:

* Tundra is a cold, treeless biome characterized by permafrost (permanently frozen ground). This makes it difficult for trees to establish roots and grow.

* Mosses, lichens, and shrubs are well-adapted to the harsh conditions of the tundra. They can tolerate the cold temperatures, short growing season, and limited water availability.

Other biomes that might feature some of these plants but are not as exclusively dominated by them include:

* Boreal Forests (Taiga): While the dominant vegetation is coniferous trees, the understory may have mosses and lichens.

* Alpine Zones: These high-altitude regions share some similarities with tundra, and can also have mosses, lichens, and low-growing shrubs.

Let me know if you'd like to know more about any of these biomes!