If Nature were to draw a map of the world what would it look like? We’ve grown accustomed to seeing the world divided into 195 countries, but there is another way to see, and better understand, the planet we call home. One Earth presents a novel biogeographical framework called Bioregions 2020, which builds upon the world’s 846 terrestrial ecoregional divisions (Dinerstein et al. 2017) to delineate 184 discreet bioregions.
Two years in development, with input from an array of field scientists, conservation experts, and geographers, Bioregions 2020 provides a framework to support grantmaking and scientific research across a group of related ecosystems. It can also be useful as an educational tool, helping people better understand the underlying ecological fabric of life that surrounds them.
While referenced frequently in scientific literature for conservation planning, the terrestrial ecoregions are often too small and too numerous to be used for country-level or large-scale regional planning efforts. In many cases the spatial configuration of one ecoregion is embedded within another and cannot be considered apart. One clear example of this is the U.S. Central Rocky Mountain Forests, which are tightly interlinked with the Montana Valley Grasslands. In other cases, groups of similar ecoregions that are adjacent to each other, for example the three northern grassland ecoregions just to the east of the Rockies, share similar attributes and thus from a conservation perspective could be considered in tandem.
One major benefit of this bioregional framework is that it allows for the integration of all three types of ecoregions – terrestrial, freshwater, and marine -- into a cohesive system. The portion of rivers, streams, lakes, and ponds that flow through a terrestrial ecoregion are included in the bioregion, and in some cases a watershed’s footprint influences the grouping of overlapping terrestrial ecoregions. Similarly, bioregions with coastal edges are extended to the corresponding country’s Exclusive Economic Zone (EEZ) boundaries. While EEZs are administrative, not biological, boundaries they do provide an ecosystem constraint as most fishing and industrial activities occur within the EEZs. “Marine Ecoregions of the World” (Spalding et al. 2007) is referenced in Bioregions 2020, and in many cases informs the clustering of terrestrial ecoregions.
The 184 bioregions are organized by the world’s eight biogeographical realms, the broadest division of the Earth's land surface within which groupings of organisms share a common evolutionary history -- Nearctic, Neotropic, Palearctic, Afrotropic, Indomalay, Australasia, Oceania, and Antarctic. The realms roughly correspond to the major continents of the Earth but are further subdivided to coincide with familiar climatic zones. For example, the Neotropical realm is divided into Central America and Southern America. These realm divisions – 14 in total -- provide the overarching content framework for the One Earth website and its Project Marketplace.
Bioregions cannot cross a realm line, so each realm contains a set grouping of bioregions:
• Subarctic America (north Nearctic): 9 bioregions
• Northern America (greater Nearctic): 22 bioregions
• Central America (north Neotropic): 6 bioregions
• Southern America (greater Neotropic): 23 bioregions
• Subarctic Eurasia (north Palearctic): 8 bioregions
• Western Eurasia (west Palearctic, aka W. Europe): 13 bioregions
• Central Eurasia (central Palearctic, aka C. Asia): 9 bioregions
• Eastern Eurasia (east Palearctic, aka E. Asia): 17 bioregions
• Southern Eurasia (south Palearctic, aka MENA): 5 bioregions
• Afrotropics (aka Sub-Saharan Africa): 24 bioregions
• Indomalaya (aka South & Southeast Asia): 18 bioregions
• Australasia: 15 bioregions
• Oceania: 11 bioregions
• Antarctica: 4 bioregions
What is a bioregion? A bioregion is a geographical area defined not by political boundaries but by ecological systems. It is smaller in scale than a biogeographical realm, but larger than an ecoregion or an ecosystem. On land, the most widely held bioregional framework is the biome or “ecozone” -- a large community of plants and animals adapted to a specific climate found over a range of continents. There are 14 widely held biome types, mapped below with an overlay of the 184 bioregions:
- Deserts & Xeric Shrublands (rust)
- Mountain Grasslands & Shrublands (beige)
- Temperate Grasslands, Savannas & Shrublands (yellow)
- Tropical & Subtropical Grasslands, Savannas & Shrublands (orange)
- Flooded Grasslands & Savannas (light blue)
- Mangroves (pink)
- Mediterranean Forests, Woodlands & Scrub (red)
- Temperate Broadleaf & Mixed Forests (dark green)
- Temperate Conifer Forests (grey-green)
- Tropical & Subtropical Coniferous Forests (light green)
- Tropical & Subtropical Dry Broadleaf Forests (olive green)
- Tropical & Subtropical Moist Broadleaf Forests (bright green)
- Boreal Forests/Taiga (medium blue)
- Tundra (teal)
Biomes provide the organizing principle used to group ecoregions into 184 discreet bioregions. Conceptually, bioregions are major subdivisions of the Earth’s biomes, formed by intersecting biome areas with large-scale geological structures -- such as mountain ranges, plains, plateaus, and basins -- or using common climatological divisions. The bioregions include adjoining freshwater and marine areas, and in some ways could be thought of as “nature’s countries” with an average land area of approximately 800,000 km2.
A consistent rule set was applied in the creation of the bioregions across all realms, but specific scientific publications pertaining to each realm were referenced in order to align the bioregions as closely as possible with commonly held ecological divisions by continent. The top-level rules used in the development of the 184 bioregions across all realms are as follows:
- Bioregions are subdivisions of the major biomes, defined most commonly by large-scale geological structures or familiar climatological zones. An example of this is the great plains of the Midwest U.S. divided into three bioregions -- north, south, and central.
- Bioregions must be contained inside one of the 14 major biogeographical realms. A bioregion cannot cross over from one realm to another.
- Bioregions consist predominantly of one biome type. In some cases, ecoregions belonging to another biome are included when those ecoregions are embedded or closely linked to the ecoregions in the adjoining biome. An example of this is the Guianan savanna, which cannot be separated from the adjacent Guianan forests.
- Ecoregions are the building blocks of each bioregion. An ecoregion is never split between two bioregions with the exception of mangroves, which often span across multiple bioregions.
- Bioregions include the marine areas beyond the coastline. These are demarcated using the EEZ boundary lines, as these waters are often heavily fished, or experience impacts from activity on adjacent land areas. In some cases, marine provinces (Spalding et al. 2007) are used to articulate a bioregion.
- Bioregional divisions are commensurate in scale to countries, with an average area of approximately 800,000 km2. Like countries, bioregions vary in scale, ranging from 100,000 km2 to 4 million km2 (not including small island states or Siberia, which has 3 large geographical divisions).
More detail is provided in each of the 14 realm breakdowns.