as physical properties (e.g., organic material in the soil), soil chemistry, soil moisture, under- 

 story solar radiation, root distribution, populations of insects and animals, and appearance. 

 These changes are often made possible through the behavior of the site's environment 

 (particularly soil and water). The ability to discern these environmental factors fiom one site 

 to another is a basis for ecological classification. Often, the plant commimity is used as an 

 indicator of these integrated environmental factors. 



Currently, the most frequently used procedure of classifying commtmity ecology follows the 

 concepts introduced by Daubenmire (1959). Many recent authors have used these concepts 

 in their woric with riparian and wetland environments (Youngblood et al. 1985, Kovalchik 

 1987, Hansen et al. 1988, Hansen 1989, Szaro 1989). These authors demonstrate that the 

 concepts of succession used in upland environments are equally applicable to riparian sys- 

 tems, although the riparian site is generally much more dynamic. It is useful in further 

 comparison and discussion to review some of the basic terminology and concepts applied in 

 these recent documents: 



Association - In normal usage, an association is a climax community type or potential 

 plant community. In riparian systems, because of their dynamic nature, a true climax 

 community may not have an opportunity to occur (Youngblood et al. 1985). An 

 association for a riparian environment is therefore a plant community type represent- 

 ing the latest successional stage attainable on a specific hydrologicaUy influenced 

 surface (Kovalchik 1987, Hansen 1989). Hansen (1989) uses the term "riparian 

 association" while Youngblood et al. (1985) chose the term "potential stable commu- 

 nity type" that approaches an association. 



Community Type - This is defined as an aggregation of all plant communities in 

 some procedures, or as existing/dominant plant communities in others. Community 

 types are distinguished by floristic and structural similarities in both overstory and 

 undergrowth layers. Community types are considered to represent serai stages. 



Site Type - This is the area of land occupied or potentially occupied by a specific 

 association. Site types that were the same would have similar environments that 

 could develop the same potential plant community. Hansen (1989) uses the term 

 "riparian site type" when describing a site capable of producing a "riparian associa- 

 tion." 



Figure 1 offers two similar views of successional concepts. Hansen (1989) provided an 

 illustration, shown in part a of Figure 1, to depict the relationship between site type, commu- 

 nity type, and association. 



The illustration shows that community types are serai to associations (potential natural 

 communities) and that some community types are common to one or more associations. It 

 also shows that one site type (range type in part b of Figure 1) supports one association 

 (PNQ. 



In many riparian systems there is a high potential for physical environments to undergo 

 sudden and/or extreme changes because of the potential for soil erosion, deposition, and 

 changes in water availability. Youngblood et al. (1985) stated "Directional processes from 

 one community type to another indicate succession; we have not attempted to indicate the 



