冻原（又称为苔原），生物群系的一种，包括极圈冻原、高山冻原生态系两类。

极圈冻原的气候非常潮湿，但却没有树木，原因在于纬度高，使得生长季非常短、冬季酷寒，表土下为永冻层更不适合木本植物，分解作用缓慢，生产力、多样性、恢复力都很低，但是生物数量却很多，几乎没有爬虫类与两栖类。

In physical geography, tundra is a type of biome where the tree growth is hindered by low temperatures and short growing seasons. The term tundra comes through Russian тундра (tûndra) from the Kildin Sami word tūndâr "uplands", "treeless mountain tract". There are three types of tundra: arctic tundra, alpine tundra, and Antarctic tundra. In tundra, the vegetation is composed of dwarf shrubs, sedges and grasses, mosses, and lichens. Scattered trees grow in some tundra regions. The ecotone (or ecological boundary region) between the tundra and the forest is known as the tree line or timberline.