Objective Ecoregions for the Continental United States

Researchers: Bill Hargrove and Forrest Hoffman

10 regions 50 regions 100 regions 500 regions 1000 regions 1500 regions 2000 regions

Problem:

Ecoregions, or regions inside which the environmental conditions are mostly similar, are of practical value to ecologists, since they highlight regional environmental differences. Gardeners may be familiar with the example of the USDA Plant Hardiness Zones map, which helps to ensure that a particular landscaping plant species will thrive in the grower's area before it is purchased.

Ecoregions are currently drawn manually using human expertise. For this reason, there are many versions of ecoregions, and they are revised frequently, since they are based subjectively on human opinion. Since they are drawn by human experts, ecoregions cannot be duplicated or repeated, and there are many disagreements.

Results:

We have developed a statistical clustering technique which allows a parallel supercomputer to generate a user-specified number of ecoregions in an objective and repeatable way. Using a set of high-resolution maps of 25 environmental characteristics, each containing over 7.8 million cells at 1 kilometer resolution, we generated maps of the 10, 50, 100, 500, 1000, 1500, and 2000 most-different ecoregions of the United States. While a human expert might be able to create maps with up to 100 ecoregions, the more finely divided maps are beyond human expertise.

Role of Computing:

The massive data sets make the determination of ecoregions an impossible task to accomplish without a parallel supercomputer. The 1000 ecoregion map would have taken more than 10.6 months of computer time if run on a serial platform, but took less than 10 days using 32 nodes of the ORNL IBM SP, the fastest non-classified parallel supercomputer in the DOE complex.

Impact:

When released, the objective ecoregion maps are expected to be well-received by ecologists, who will be able to select from the series the level of division which is best suited for their particular area and use.