laws and multiple use mandates are to be complied with. It has therefore been 

 recognized that an integrated classification system is needed. 



In the United States work to develop such a system over the past decade has 

 involved the ecosystem concept.^ Ecological land classification refers to an integrated 

 survey approach in which areas of land, as ecosystems, are classified according to 

 their ecological unity. This paper presents an overview of some of the best-known 

 classification systems and highlights future needs. 



THE ECOSYSTEM CONCEPT 



The ecosystem concept regards the earth as a series of interrelated systems in which 

 all components are linked, so that a change in any one component may bring about 

 some corresponding change in other components and in the operation of the whole.* 

 An ecosystem approach to land evaluation stresses the interrelationship among 

 components rather than treating each one as a separate characteristic of the 

 landscape. 



One of the more significant aspects of ecosystems in assessment and planning is 

 that they constitute real units of the natural world and can be approximately 

 identified on the ground. Thus, they form logical operating units for environmental 

 planning and direction. Rowe defined an ecosystem as ". . .a topographic unit, a 

 volume of land and air plus organics contents extended areally over a particular part 

 of the earth's surface for a certain time."' As such, ecosystems are discrete geographic 

 units of the landscape that include all natural phenomena and that can be identified 

 and surrounded by boundaries. 



The boundaries of ecosystems, however, are never closed or impermeable; they are 

 open to transfer of energy and materials to or from other ecosystems. The open 

 nature of ecosystem boundaries is important, for the exchange of material with its 

 surroundings is an important aspect of the system's operation. 



The term ecosystem is used quite generally without reference to spatial dimen- 

 sions.* The largest ecosystem is formed by the planet Earth; examples of small 

 ecosystems include a narrowly limited, homogeneous stand of vegetation or a small 

 pond. In order to cover all ecosystems at all levels of planning and management, it is 

 necessary to set up a defined hierarchy of ecological units of different sizes. Since 

 ecosystems are spatial systems, they will be consistently inserted, or nested, into each 

 other. Each level subsumes the environment of the system at the level below it. At 

 each level, new processes emerge that were not present or not evident at the next 

 lower level. As Odum^ noted, results at any one level aid the study of the next higher 

 level but never completely explain the phenomena occurring at that level, which itself 

 must be studied to complete the picture. 



The aim of ecological land classification is to provide a system that expresses the 

 interactive character of the ecosystem's components, viz. soil, water, climate, flora, 

 and fauna. Such classification also embodies the relationship between systems of 

 different size in a spatial hierarchy. Instead of stressing an isolated component of the 

 system, it focuses on a holistic concept of land which considers arrangements in space 

 and time and processes that emerge from them. 



Ecological classification systems are essential to any resource management effort. 

 By identifying geographic areas as ecosystems with similar properties, these systems 

 permit the design of cost-effective sampling programs and the aggregation of 

 information. Because similar ecological units can be expected to respond in hke 

 manner to similar management practices or environmental stresses, classification 

 systems increase our ability to generalize, to extrapolate research results, and to 

 transfer management experience. There is not yet a generally accepted ecosystem 

 classification system guiding federal and state agencies in wildlife habitat manage- 

 ment.* The development of compatible systems for inventories of natural resources is 

 critically needed in order to coordinate future management efforts. 



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