What Is a Biome?

Biomes are the broadest classification of Earth ecosystems, determined primarily by temperature and precipitation patterns. Ecologists generally recognise 5-8 major terrestrial biomes: tropical rainforest, temperate forest, boreal forest (taiga), grassland/savanna, desert, tundra, and Mediterranean scrubland, plus freshwater and marine biomes. Each biome supports characteristic plant and animal communities adapted to its conditions. Tropical rainforests, covering only about 6% of Earth land surface, contain over 50% of all terrestrial species. Tundra biomes have permafrost (permanently frozen ground) that limits plant growth to mosses, lichens, and dwarf shrubs. Climate change is shifting biome boundaries — boreal forests are expanding northward, deserts are expanding at their margins, and coral reef biomes are under severe thermal stress.