recorded the environmental factors of elevation, aspect, 

 landform, and soil parent material, and also location and 

 interpretative information related to succession and ani- 

 mal use. 



Data from 1,233 aspen stands were accumulated in 

 this manner to form the basis for describing the aspen 

 communities in Utah. We sampled 421 of these stands 

 intensively; the remaining 812 were sampled by the 

 reconnaissance technique. 



Data Analysis 



Prior to placing the field data on computer file for 

 analysis, we confirmed the identification of voucher 

 plant specimens and identified the collections of ques- 

 tionable species. The coding and key-punching of all 

 vegetation and environmental data were checked for 

 errors. 



Development of the classification categories relied 

 principally upon use of synthesis or association tables 

 (Mueller-Dombois and EUenberg 1974). Before the proc- 

 ess of stand alignment and reiteration began, every 

 tenth stand was temporarily deleted from the file to 

 serve as an unbiased validation of the classification that 

 would be developed, and validation of the field key con- 

 structed to assist in identification of the community 

 types. These vahdation stands were subsequently rein- 

 troduced into the data file for compilation of all tables 

 summarizing the community type data. The synthesis 

 table method permitted subjective recognition of similar- 

 ities in vegetation structure and in species fidelity, con- 

 stancy, and coverage. We considered certain species to 

 be indicative of natural succession, environment, grazing 

 degradation, and management concerns; numerous reiter- 

 ations of stand alignments permitted sequencing accord- 

 ing to visual similarities of these important species. 



We subsequently grouped the stands into community 

 types according to the constancy and abundance of the 

 selected indicator species. Similarity of vegetational 

 structure was a prime consideration in forming the 

 groups. The presence or absence of substantial amounts 

 of conifers in the overstory, or potentially so as judged 

 by conifer regeneration, was the first separation 

 criterion. These were categorized as aspen-conifer cover 

 types (table 1). The presence of substantial amounts of 

 conifers was considered highly relevant because of suc- 

 cessional impUcations. In the normal course of succes- 

 sion, all such mixed cover types will probably succeed to 

 coniferous forest climax communities. The presence of a 

 tall shrub layer and of a low shrub layer were the second 

 and third criteria considered in grouping stands. These 

 shrub layers not only tend to reflect environmental 

 differences but are also highly relevant to management. 



We selected the indicator species in the herbaceous layer 

 as the most sensitive indicators of abiotic environmental 

 extremes and of severe vegetational alterations caused 

 by prolonged excessive grazing. Thus, species' preva- 

 lence within the tree, shrub, and herb life-form classes 

 were used to deUneate and characterize the aspen com- 

 munity types. 



After we grouped the stands into what appeared to be 

 sensible community types, we prepared a dichotomous 

 key based upon characterizing species and checked 

 against all stands used to develop the classification. This 

 key was developed to faciUtate field use of the classifica- 

 tion. The last step was to use the key to classify the 

 validation stands into community types and then to 

 compare the species composition of these groups with 

 that of the original groups used to develop the classifica- 

 tion. Less than 5 percent of the original stands used to 

 form the classification could not readily be placed into 

 identifiable community types. Similarly, about 3 percent 

 of the validation stands did not fit the classification. 

 These undetermined stands (20 intensively sampled and 

 34 reconnaissance) are likely either unusual isolated com- 

 munities, or else represent ill-defined community types 

 reflecting restricted environmental situations. 



Whether a community is serai or stable can apprecia- 

 bly affect management decisions. Therefore, the ability 

 to judge the successional status of the aspen community 

 types is important. Community stability is indicated 

 when existing individuals are replaced by their own 

 progeny, without disturbance; thus, the community is 

 self-perpetuating. In serai communities, current popula- 

 tions of some species tend to be replaced by other spe- 

 cies, resulting in gradual changes in composition. 

 Although accurate determination of community stability 

 may require intensive ecological study, preUminary 

 determinations are possible by comparing vegetational 

 composition with that of communities of known stabil- 

 ity, evaluating the age structure of the woody species 

 and the proportions of shade-tolerant species, and 

 examining the relative abundance of species known to 

 increase with such disturbance as excessive livestock 

 grazing. We have attempted to clarify the successional 

 status of the aspen community types in Utah by linking 

 them to either Mauk and Henderson's (1984) coniferous 

 forest habitat type classification for northern Utah, or to 

 Youngblood and Mauk's (1985) classification for central 

 and southern Utah, and to other community types in our 

 aspen classification. At best, the linkages are only sug- 

 gestive and will require intensive separate study for con- 

 firmation of the successional relationships. Our judg- 

 ments of the successional status of each community type 

 are shown in table 2. 



4 



