What is the main factor that makes the tundra unique among biomes?

The tundra is uniquely characterized by its permafrost, which is a layer of ground that remains frozen throughout the year. This permanent frost creates specific conditions that influence the types of vegetation and wildlife that can inhabit this biome. In tundra regions, the harsh climate and short growing seasons limit plant growth primarily to mosses, lichens, and low shrubs, as larger trees cannot take root in the frozen ground.

The presence of permafrost also affects drainage and soil composition, leading to waterlogged conditions during the brief summer thaw, contributing to the unique ecosystem found in the tundra. Consequently, this aspect of having ground that is perpetually frozen is crucial in defining the tundra, setting it apart from other biomes that do not share the same climatic and geographic features.