Conservation of the Earth's biological diversity requires a clear understanding of the distribution and condition of the components that comprise it. Efforts to understand our natural world are directed at a variety of scales across biology -- genes and species -- and ecology -- natural communities, local ecosystems, and landscapes. While scientists have made considerable progress classifying fine-grained ecological communities on the one hand, and coarse-grained ecoregions on the other, land managers have a critical need for practical, mid-scale ecological units to inform conservation and resource management decisions. Ecological systems provide this important mid-scale unit of classification.
Ecological systems represent recurring groups of living organisms found in similar physical settings and influenced by similar dynamic processes like fire or flooding. For conservationists and resource managers, ecological systems providing a classification unit that is readily mappable, often from remote imagery, and readily identifiable in the field.
In 2003, NatureServe and its natural heritage program members, with funding from The Nature Conservancy, completed a working classification of terrestrial ecological systems in the coterminous United States, southern Alaska, and adjacent portions of Mexico and Canada. The classification describes over 600 upland and wetland ecological systems, documenting them for applications in conservation assessment, ecological inventory, mapping, land management, ecological monitoring, and species habitat modeling.
Terrestrial ecological systems are specifically defined as a group of plant community types, or associations, that tend to co-occur within landscapes with similar ecological processes, substrates, and/or environmental gradients. A given system will typically manifest itself in a landscape at intermediate geographic scales of tens to thousands of acres and will persist for 50 or more years. The addition of this temporal scale allows the integration of typical successional dynamics into the concept of each unit. With these temporal and spatial scales bounding the concept of ecological systems, we then integrate multiple ecological factors—or diagnostic classifiers—to define each classification unit. The multiple ecological factors are evaluated and combined in different ways to explain the spatial co-occurrence of plant associations.
Terrestrial ecological system units represent practical, systematically defined groupings of plant associations that provide the basis for mapping terrestrial communities and ecosystems at multiple scales of spatial and thematic resolution. The systems approach complements the U.S. National Vegetation Classification, whose finer-scale units provide a basis for interpreting larger-scale ecological system patterns and concepts. This working classification serves as the basis for NatureServe’s facilitation of the ongoing development and refinement of the U.S. component of an International Terrestrial Ecological Systems Classification.