Terrestrial ecological communities may be categorized into four functional groups on the basis of
their current or historical patterns of occurrence, as correlated with the distribution and extent of landscape
features and ecological processes. These groups are identified as matrix communities,
large patch communities, small patch communities, and
linear communities.
Matrix Communities
Ecological communities that form extensive and often contiguous cover may be categorized as matrix (or matrix-forming)
community types. Matrix communities occur on the most extensive landforms and typically have wide ecological
tolerances. Individual Element occurrences of the matrix type typically range in size from 2000 to 405,000 hectares
(approximately 5000 to 1,000,000 acres). In a typical ecoregion, the aggregate of all matrix communities
covers, or historically covered, as much as 75-80% of the natural vegetation of the ecoregion. Any matrix occurrence is likely to have large patch and small patch occurrences embedded within it. Matrix community types
are often influenced by large-scale processes (e.g., climate, fire), and are important habitat for wide-ranging or
large area-dependent fauna, such as large herbivores or birds (e.g., bison, prairie chickens).
Large Patch Communities
Ecological communities that form large areas of interrupted cover may be categorized
as large patch community types. Individual EOs of this community type typically range in size from 20 to 2000
hectares (approximately 50 to 5000 acres). Large patch communities are associated with environmental
conditions that are more specific than those of matrix communities, and that are less common or less extensive in
the landscape. In a typical ecoregion, the aggregate of all large patch communities covers, or historically
covered, as much as 20% of the natural vegetation of the ecoregion. Like matrix communities, large patch community
types are also influenced by large-scale processes, but these tend to be modified by specific
site features that influence the community.
Small Patch Communities
Ecological communities that form small, discrete areas of cover may be categorized
as small patch community types. Individual EOs of this community type are typically 20 hectares (approximately
50 acres) or less. Small patch communities occur in very specific ecological settings, such as on specialized
landform types or in unusual microhabitats. In a typical ecoregion, the aggregate of all small patch communities covers, or historically covered, only as much as 5% of the natural vegetation of the ecoregion.
Small patch community types are characterized by localized, small-scale ecological processes that can be quite
different from the large-scale processes operating in the overall landscape. The specialized conditions
of small patch communities, however, are often dependent on the maintenance of ecological processes in the
surrounding matrix and large patch communities. In many ecoregions, small patch communities contain a
disproportionately large percentage of the total flora, and also support a specific and
restricted set of associated fauna (e.g., invertebrates, herpetofauna) dependent on specialized conditions.
Linear Communities
Ecological communities that form as linear strips are often, but not always, ecotonal
between terrestrial and aquatic systems. Examples include coastal beach strands, bedrock lakeshores, and narrow
riparian communities. Similar to small patch communities, linear communities occur in very specific
ecological settings, and the aggregate of all linear communities covers, or historically covered, only a small
percentage of the natural vegetation of the ecoregion. They also tend to support a specific and restricted
set of associated flora and fauna. Linear communities differ from small patch communities in that both local
scale processes and large scale processes, such as lake/ocean currents or riverine flow regimes, strongly
influence community structure and function. This characteristic often leaves these communities highly
vulnerable to alterations in the surrounding land and waterscape.
Source: Draft
Element Occurrence Data Standard
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