Forest Atlas Of The United States

Ecological Divisions of North America

The earth’s surface can be broken into progressively uniform units based upon climate, plants, and soil; some classification systems even include human management. The Forest Service’s system of classifying the landscape starts at the broadest scale with four domains defined by precipitation and temperature: polar, humid, dry, and humid tropical. Divisions further subdivide domains, and are identified by more detailed separation in precipitation amount and pattern, along with temperature. These classifications are useful tools for understanding ecological variation across the landscape.

Managers, scientists, and others involved with ecological issues use a wide variety of classification systems. In biology, plants and animals are classified to better identify and understand their similarities and differences. Similarly, landscape ecologists divide the earth’s surface using progressively smaller and more uniform units to facilitate resource management across the landscape. These units — domains, divisions, provinces, sections — are important to forests because similar landscapes support similar types of forests.

Landscapes are generally classified based upon climate, vegetation, and soil. A few management-oriented classifications include agricultural crops and other human factors. The importance of each factor varies among units, but climate is the starting point for dividing the landscape in this system. Temperature and available moisture, and the timing of each, influence both plant communities and soil development. And while a site’s climate is strongly related to latitude and its location on the continent (near the ocean or deep in the interior), mountains have a profound influence and create their own ecosystems.

When applied at broader scales, landscape classification systems can be used to put ecosystems into an international context. These systems also facilitate management of environmental issues occurring over large areas or transcending political and agency boundaries.

As landscape units get smaller, they also become more homogenous. For the sake of simplicity, this map focuses upon ecological divisions, a midpoint in the Forest Service’s landscape classification system.

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Icecap Tundra Subarctic Warm Continental Hot Continental Subtropical Marine Prairie Mediterranean Tropical/Subtropical Steppe Tropical/Subtropical Desert Temperate Steppe Temperate Desert Savanna Rainforest Mountains with altitudinal zonation

ECOLOGICAL DIVISIONS OF CANADA, THE UNITED STATES, AND MEXICO. A strong temperature gradient from north to south is evident in this map with tundra and subarctic divisions in the north transitioning to subtropical, rainforest, and desert divisions in the south. A precipitation gradient from the East Coast across the Great Plains to the Rocky Mountains is also visible. A thin strip of marine ecosystems hug the Pacific coast, and the wet winters and dry summers of California are captured by the Mediterranean division. Mountains across the continent (noted by hash marks on the map) create large variations in climate and vegetation over short distances.

AREA OF FOREST LAND (million acres) AREA OF FOREST LAND (million acres) 0 20 40 60 80 100 120 140 160 ECOLOGICAL DIVISION Warm Continental Savanna