Ecozones: Earth's Major Ecological Divisions

Ecozones: The Planetary Scale of Ecological Organization

An ecozone (or biogeographic realm) is the largest scale of ecological classification, representing vast regions where ecosystems share broadly similar evolutionary histories, climatic regimes, and biotic assemblages. Ecozones encompass multiple biomes.

WWF's 14 Terrestrial Ecozones (Olson et al. 2001)

1. Palearctic: Europe, North Africa, N/central Asia, N Japan. Temperate/boreal forests, steppes, tundra.
2. Nearctic: N. America, Greenland, N. Mexico. Boreal forest, temperate forest, grasslands, deserts.
3. Neotropical: Central/South America, Caribbean. Tropical rainforest, savanna, Andes, Atacama.
4. Afrotropical: Sub-Saharan Africa. Savanna, Congo rainforest, Cape fynbos, Madagascar.
5. Indo-Malayan: South/Southeast Asia, S. China. Tropical rainforest, Himalayas, Sundaland.
6. Australasian: Australia, New Guinea, NZ, Pacific islands. Sclerophyll, rainforest, alpine, reef.
7. Oceanian: Micronesia, Melanesia, Polynesia. Tropical islands, atolls, reefs.
8. Antarctic: Antarctica + Southern Ocean islands. Ice desert, coastal tundra.

Additional WWF ecozones (freshwater/marine focused): Mediterranean Basin, Tundra, Temperate Coniferous Forests, Tropical/Subtropical Dry Broadleaf Forests, Deserts/Xeric Shrublands, Mangroves.

Alternative Systems

• Udvardy (1975): 8 biogeographic realms (similar to WWF terrestrial).
• Cox (2001): 7 realms + transition zones.
• Marine Ecoregions (Spalding et al. 2007): 12 realms, 62 provinces, 232 ecoregions.
• Freshwater Ecoregions (Abell et al. 2008): 11 realms, 426 ecoregions.

Significance

Ecozones reflect deep evolutionary isolation (continental drift). They guide global conservation prioritization (WWF Global 200), predict invasive species risk, and frame climate change vulnerability assessments. Each contains unique lineages—e.g., marsupials (Australasian), lemurs (Afrotropical/Madagascar), hummingbirds (Neotropical).

Hierarchy

Ecozone → Biome → Ecoregion → Habitat → Microhabitat. Ecozones are continental; biomes are climatic (e.g., tropical rainforest appears in Neotropical, Afrotropical, Indo-Malayan, Australasian ecozones with different species).