Table 3. Regional definitions explored. Number of regions Defined as: 4 Highest level of aggregation on the ecosystem map of Bailey et al., i.e., Arctic, temperate, arid, and tropical 14 Fourteen natural biome types defined in IMAGE, i.e., ice, tundra, wooded tundra, boreal forest, mixed conifer, temperate broadleaf forest, temperate mixed forest, warm mixed forest, grasslands, desert, shrubland, savannah, tropical woodland, tropical forest 24 Intersection of the highest level of Bailey’s map, i.e., Artic, temperate, arid, and tropical, with the six biogeographic regions of the Olson map. This roughly corresponds to the second layer of the Bailey map. 65 Intersection of Olson’s map of ecosystem realms with the 14 IMAGE natural biomes 75 Based on the previous (65) regional definitions, but now adding two more realms, i.e., the Cape region in South Africa and East Asia and Japan, again intersecting with the 14 IMAGE natural biomes.