The Global 200 : a representation Approach to Conserving the Earth’s Distinctive Ecoregions

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The Global 200:

A Representation Approach to Conserving the Earth’s Distinctive Ecoregions

David M. Olson, Eric Dinerstein, Robin Abell, Tom Allnutt, Christopher Carpenter, Loren McClenachan, Jennifer D’Amico, Patrick Hurley, Ken Kassem, Holly Strand, Meseret Taye, and Michele Thieme

Conservation Science Program, World Wildlife Fund-US

1250 24th Street, NW, Washington, DC, 20037 USA

E-mail: /

October 2000


Much conservation attention has focused on the preservation of tropical moist forests (rain forests) because they harbor an estimated 50 percent of species on Earth. However, a comprehensive strategy for conserving global biodiversity should strive to save the other 50 percent of the species and the distinctive ecosystems that support them. Tropical dry forests, tundra, temperate grasslands, lakes, polar seas, and mangroves all contain unique expressions of biodiversity with characteristic species, biological communities, and distinctive ecological and evolutionary phenomena. Some of these major habitat types (i.e., biomes), such as tropical dry forests and Mediterranean-climate shrublands, are on average more threatened than are tropical moist forests and require immediate conservation action.

To better incorporate representation of the Earth’s distinctive ecosystems in conservation strategies, we conducted an analysis of ecoregions representing the Earth’s 30 terrestrial, freshwater, and marine major habitat types. Based on a comparative global analysis and synthesis of five extensive regional studies, we identified 238 ecoregions as priority targets for conservation action because they harbor the most outstanding and representative examples of the world’s diverse ecosystems. These 238 ecoregions—the Global 200—are comprised of 142 terrestrial, 53 freshwater, and 43 marine ecoregions. Selection of ecoregions was based on analyses of species richness, species endemism, unique higher taxa, unusual ecological or evolutionary phenomena, and global rarity of major habitat types. We selected outstanding ecoregions within each major habitat type from each of the world’s biogeographic realms and ocean basins to better capture the variation in species assemblages around the world.


The current extinction crisis requires dramatic action to save the Earth’s biological diversity (biodiversity), that is, the variety of life expressed at many levels. These levels include the genetic diversity within species as well as the array of genera; families, and still higher taxonomic levels that, taken together, comprise communities of organisms within particular habitats and physical conditions that form entire ecosystems. Because funding for conservation action aimed at preserving biodiversity is limited, governments, donors, and conservation groups must be strategic and earmark the greatest amount of resources for protecting the most outstanding and representative areas for biodiversity. Most conservation biologists recognize that although we cannot save everything, we should at least ensure that all ecosystem and habitat types are represented within regional conservation strategies (Hummel 1989, Caldecott et al. 1994, Krever et al. 1994, Noss & Cooperrider 1994, BSP et al. 1995, Dinerstein et al. 1995, UNEP 1995, Ricketts et al. 1999, Abell et al. 2000).

The “representation” approach has been applied at a number of geographical scales, from single watersheds to entire continents (UNESCO 1974, Hummel 1989, Nicoll & Langrand 1989, Bedward et al. 1992, Scott et al. 1993, Pressey & Logan 1994, Pressey et al. 1994, Cox et al. 1994, MacKinnon 1994, Dinerstein et al. 1995, Fearnside & Ferraz 1995, Johnson 1995, Noss & Peters 1995). Here we introduce the Global 200, the first attempt to achieve representation of all major habitat types at a global scale. Our primary objective is to promote the conservation of distinctive terrestrial, freshwater, and marine ecosystems harboring globally important biodiversity and ecological phenomena. The Global 200 addresses this goal by identifying the world’s most outstanding examples within each major habitat type (e.g., tropical dry forests, large lakes, coral reefs).

The representation approach, accepted by a growing number of conservationists, is soundly based in conservation biology. It integrates the goal of maintaining species diversity (the traditional focus of biodiversity conservation) with another level of conservation action—the preservation of distinct ecosystems and evolutionary phenomena. While it is true that more than half of all species are likely to occur in the world’s tropical moist forests, the other 50% of all species are found elsewhere. To conserve this half, a full representation of the world’s diverse ecosystems must be the goal.

Tundra, tropical lakes, mangroves, and temperate broadleaf forests are all unique expressions of biodiversity. Although they may not support the rich communities seen in tropical rain forests or coral reefs, they contain species assemblages adapted to distinct environmental conditions and reflect different evolutionary histories. To lose representative examples of these assemblages and the evolutionary phenomena they contain, would represent an enormous loss of biodiversity.
Although conservation action typically takes place at one of several governmental levels—whether it be the local, state/federal, national, or even multinational level (e.g., the European Union)—patterns of biodiversity and ecological processes (e.g., migration) do not conform to political boundaries. Thus, we used ecoregions as the unit of analysis in creating the Global 200. We define an ecoregion as a relatively large unit of land or water containing a characteristic set of natural communities that share a large majority of their species, dynamics, and environmental conditions (Dinerstein et al. 1995, TNC 1997). Ecoregions function effectively as conservation units at regional scales because they encompass similar biological communities and their boundaries roughly coincide with the area over which key ecological processes most strongly interact (Orians 1993, Noss 1996).

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