Ecological Mapping

Ecological maps are playing an increasing role in land management and planning. Their purpose is to display units of land of various sizes that reflect differences in response to management and resource production capability. An ecological map shows an area divided into ecosystems—that is, areas within which there are associations of interacting biotic and abiotic features. How these features are associated or integrated can be shown at two general levels. One level shows the integration within the local level, and another shows how the local area is integrated and linked with other areas across the landscape to form larger systems. All these areas are ecosystems, albeit at different scales or relative sizes.

Subdivision of land into systems of different sizes is needed for several reasons. Because of the linkages between systems, a modification of one system may affect the operation of surrounding systems. Furthermore, how a system will respond to management is partially determined by relationships with the surrounding systems linked in terms of runoff, groundwater movement, and microclimate influences. Because ecosystems are spatially nested in each other, each level subsumes the environment of the system at the level below it. Therefore, it conditions or controls the behavior of the system at the level below it. Understanding these relationships is important in analyzing cumulative effects of action at one scale and its effects at another.

Given this need, landscape ecologists and ecosystem geographers have been interested in hierarchical schemes of ecosystem units. The nomenclature and number of levels in these schemes vary. One scheme that has been adopted by the U.S. Forest Service and others for use in ecosystem management recognizes ecosystems at three scales of perception. The smallest, or microscale, ecosystems are the homogeneous sites commonly recognized by foresters and range scientists. At the mesoscale, linked sites create a landscape mosaic that looks like a patchwork. At the macroscale, mosaics are connected to form larger systems. These units of connected mosaics are called ecoregions.

The fundamental question facing all ecological land mappers is “How are the boundaries of different-sized systems to be determined?” Different methods have been used to identify units where ecosystem components are integrated in a similar way, thereby classifying land as ecosystems. One method is to overlay maps of ecosystem components at a similar resolution to look for associations of these components to identify ecological units with similar patterns. Some ecosystem mappers have employed a gestalt approach in which boundaries are drawn intuitively around areas that appear homogeneous. Others used multivariate clustering to classify grid cells. A map is produced by drawing lines around cells of similar class. These methods are termed empirical because they are descriptive and do not explain why units should be distinguished.

In an alternative to the empirical approach, a major emphasis is on mechanisms that produce the pattern of ecosystem distribution. Establishing a hierarchy of ecosystem boundaries is based on an understanding of the formative processes that operate to differentiate the landscape into ecosystems at various scales. The units derived from such an approach are termed genetic in that they are predicated on an understanding of the causal processes that control the pattern of ecosystems. Understanding spatial relationships between causal mechanisms and resultant patterns is key to understanding how ecosystems respond to management.

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