RESULTS 



COMMUNITY TYPES 



The previously described cluster analysis and classification resulted 

 in the identification of twenty-seven community types whose names, along 

 with their abbreviations are listed in Table 1. Figure 3 shows the general 

 results of the dendrogram and classification. The types are discussed in 

 general followed by separate discussions of species composition, sites, 

 species diversity, and productivity. 



Figure 3 is a rendition of the dendrogram as classified. "ZAP Plots", 

 which appear in the figure, refer to floristic data for the study sites in 

 trie Zonal Air Pollution System (Taylor et al. 1975). These data were used 

 in the cluster analysis in the hope that, based on their similarity to 

 other communities, impact predictions could be based in part upon studies 

 near Colstrip. Unfortunately, the ZAP communities were segregated from the 

 types in the study area on the basis of their high coverages of Bromis 

 tectorum and B^. japonicus . 



The term community type refers to an abstract grouping of communities 

 which are similar enough in their species composition to warrant recognition 

 as a class. Community types are not habitat types or units of land named 

 for the climax plant association. Although speculation is sometimes made 

 about successional status, no study of population dynamics or successional 

 trends has been made. 



General Discussion of Community Types 



Scirpus americanus Community Type (Scam c.t. ). The Scam c.t., a 

 minor type having a restricted extent within the study area, is a monocul- 

 ture, or nearly so, occuring on alkaline areas that are flooded at least 

 part of the year, and on heavy soils along salty streams. The soils of the 

 Scam c.t. have low redox potential. Soil moisture at rooting depth is 

 seldom below field capacity and at other times S^. americanus is emergent. 

 Sites for the Scam c.t. are moister than sites for the Distichlis stricta 

 community type, which can often be found adjacent to Scam c.t. sites. 



The Scam c.t. appears to be similar to the S^. paludosus {S_. maritimus L. ) 

 community type of Ungar (1974). Coupland (1950) notes S^. paludosus dom- 

 inance in the moister or better drained parts of salt flats. Stewart and 

 Kantrud (1972) identified S^. americanus as a dominant associated with grazing 

 and sandy soil in moderately brackish, shallow marshes in North Dakota. 



Communities of Juncus , Carex , and Eleocharis are occasionally found 

 along brackish streams near the Scam c.t. Triglochin maritimu m. and 

 Schedonnardus paniculatus are sometimes present in this type. 



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