Ecological Systems Classification

Palouse prairie remnant at Kahlotus NAP
Palouse prairie remnant at Kahlotus NAP

The Ecological Systems classification was developed by NatureServe to provide a mid-scale ecological classification, for uplands and wetlands, useful for conservation and environmental planning. Ecological Systems represent recurring groups of terrestrial plant communities that are found in similar climatic and physical environments and are influenced by similar dynamic ecological processes, such as fire or flooding, share similar substrates, and/or environmental gradients. Ecological systems include natural to semi-natural vegetation. Natural to semi-natural vegetation has a species composition primarily determined by nonhuman ecological processes.  Cultural vegetation is primarily a response to human intervention such as suburban lawns or apple orchards.
Both temporal and spatial scales are used to define ecological system types.  Temporal variability in biotic composition is accounted for by including early-, mid-, and later-seral vegetation (i.e. plant associations) into one classification unit, assuming succession progresses within a 50 year time frame. Ecological Systems occur at a spatial scale ranging from a few to 1000s of hectares and persist for more than 50 years.  The spatial pattern in which each Ecological System occurs on the landscape can be described using four spatial categories:
  1. Matrix: contiguous cover ranging from 2,000 to 10,000 hectares; occur on the most extensive landforms and typically have wide ecological tolerances.
  2. Large patch: large areas of interrupted cover ranging from 50 to 2,000 hectares and have narrower range of ecological tolerance.
  3. Small patch: small, discrete areas ranging from 1-50 ha and limited in distribution by localized ecological processes.
  4. Linear: occur as linear strips ranging in distance from 0.5 to 100 km; often ecotonal between terrestrial and aquatic ecosystems.
These spatial patterns are hierarchical in that the large patch, small patch, and linear Ecological Systems are, in a natural landscape, nested within a matrix Ecological System.  This does not imply that each occurrence of a matrix Ecological System will have a finer-scale type within it, but smaller patch types will always occur within or adjacent to larger-scale patch types.
The Ecological Systems classification describes over 800 upland and wetland ecological system types found in the United States, and in adjacent portions of Mexico and Canada. Ecological Systems facilitate mapping at meso-scales (1:24,000 – 1:100,000). Terrestrial ecological systems have formed the basis for map legends on national mapping efforts, including the inter-agency LANDFIRE and Gap Analysis Program efforts. The results of these large-scale mapping projects have been combined into a map of ecological systems for the United States (Sayre et al. 2009). The Washington portion of the map can be viewed on Landscope or downloaded here. Due to the scale of the mapping, many small patch systems such as wetlands or balds are either underrepresented or not included in the map.
Nomenclature for Ecological System is based on three components:  regional distribution (e.g. North Pacific), environmental characteristics (e.g. Mesic), and vegetation physiognomy and composition (e.g. Western Hemlock-Silver Fir Forest). The Ecological System name for this example is: North Pacific Mesic Western-Silver Fir Hemlock Forest.
Washington Natural Heritage Program (WNHP) ecologists have developed a guide to Washington’s Ecological Systems as well as an assessment of each Ecological Systems conservation status.
WNHP uses Ecological Systems for large-scale objectives and the U.S. National Vegetation Classification (USNVC) to address fine-scale objectives.  Specifically, WNHP uses the Ecological Systems classification to provide a framework and common language to:
  • Represent a coarse-filter for biodiversity conservation and/or management plans at a mid-scale classification -between ecoregions and associations.
  • Map existing vegetation at the coarse scale, which can provide the foundation for various GIS models. The availability of wall-to-wall map of Ecological Systems allows the classification framework to be used for a variety of modeling applications. For example, species distribution modeling, landscape integrity assessments, habitat loss models, etc.
  • Promote study and appreciation of native ecosystems in Washington. Ecological Systems are often a more intuitive concept for the nonspecialist to grasp compared to the USNVC.
In contrast, WNHP uses the USNVC to provide a framework and common language to:
  • Represent a fine-scale, ecosystem filter (i.e., associations) for biodiversity conservation and/or management plans.
  • Map existing vegetation at fine (i.e. associations) to very coarse (formations class), which can provide the foundation for various conservation and management objectives, ecological monitoring, and scientific research.

Relevant technical resources: