Ecoregions

There is an increasing realization that natural resources do not exist in isolation but interact with each other. Understanding this has led to a focus on a more holistic approach of managing whole ecosystems that considers both biotic and abiotic components of the ecosystems. Ecosystems are of different sizes and can be identified at multiple scales in a hierarchy. The smaller systems are embedded, or nested, within larger macroscale ecosystems. The larger systems are the environments that control their behavior. By understanding the larger forces that create macroscale ecosystems, we can better predict how management practices will affect smaller local systems. At the macroscale, ecosystem patterns are controlled by macroclimate (i.e., the climate that lies just beyond the local modifying irregularities of landform and vegetation). Over large continental areas, macroclimatic units—also termed ecoclimatic zones or ecological zones—are reflective of those ecosystems at the macroscale that biogeographers have recognized as ecosystem regions, or ecoregions. Based on macroclimatic conditions, they have developed systems that classify the natural ecoregions of Earth (Figure 1). Ecoregion classification is hierarchical in that mapping is accomplished at different scales. These classification systems are similar but differ in the hierarchical arrangement used.

The fundamental question facing ecological land mappers is “How are the boundaries of different size systems determined?” Delineating units involves analyzing the controlling factors that cause ecosystem patterns at various scales and then using significant changes in controls as boundaries. Areas of uniform climate are used to identify ecosystem units because climate acts as the primary input of energy and moisture into the system. As the climate changes, the kinds and patterns of dominant life forms of plants and animals change, as do the kinds of soils. Ecosystems of different climates differ significantly. Controls over the climatic effect change with scale. Understanding these controlling factors and the scale at which they operate is key to setting ecosystem boundaries.

Ecoregion subzones or provinces such as savanna, steppe, or tundra correspond to major [Page 856]plant formations, which are delimited on the basis of features of the vegetation. These subdivisions express more refined climatic differences than do the zones. Mountainous provinces are distinguished within a zone where, as a result of altitude, the climate differs sufficiently from the adjacent lowlands to cause a typical sequence of altitudinal belts.

Figure 1 Ecoregion divisions map (Level 2 of the ecoregion hierarchy) of the world

Source: Bailey, R. G. (1996). Ecosystem geography (Plate 1). New York: Springer-Verlag.

Within an ecoregion, landforms, through varying height and degree of ground surface inclination, further modify the macroclimate to local climate to form repeated patterns of smaller ecosystems, called sites. By observing the behavior of the different kinds of systems in a region, it is possible to predict the behavior of an unvisited one. Hence, an ecoregion's map can be used to spatially extend data obtained from limited sample sites. The results of observations at representative sample sites from each ecoregion would be potentially useful in detecting and monitoring global change effects.