Data Analysis 



Analysis focused on using a combination of (1) 

 classification, to determine community types, and (2) ordination 

 (gradient analyses) , to describe general patterns of communities 

 in relation to environmental factors. Classification was 

 accomplished using two-way indicator species analysis (TWINSPAN; 

 Hill 1979a) in the CEP MS-DOS computer package (Mohler 1987) . 

 Ordination was achieved using the detrended correspondence 

 analysis (DCA) algorithm in the CANOCO computer package (Ter 

 Braak 1988). The input data were species cover variables 

 recorded in each plot. Both TWINSPAN and DCA are based on the 

 same mathematical strategy (i.e., reciprocal averaging; Hill 

 1979a, b) and thus offer direct comparisons between the results of 

 ordination and classification. 



All default options in the TWINSPAN algorithm were used 

 except that pseudospecies cut levels were set at , 2, and 20 

 percent cover and pseudospecies weights were changed from 111 

 to 1 2 4 (i.e., pseudospecies at the second and third cut levels 

 were given twice and four-times, respectively, the weight of 

 pseudospecies at cut level one) . Also, all default options were 

 used in running DCA except that rare species were downweighted. 

 Initially, the entire data matrix of 197 stands and 365 species 

 was analyzed. Subsequently, to reduce the amount of variation 

 being considered, which is substantial in the whole matrix, the 

 species list was thinned to the 194 most characteristic species 

 and analyses were conducted on forest/woodland, woodland, and 

 shrubland/grassland subgroups. 



In some instances, a particular TWINSPAN class included a 

 plot or plots that, based on field experience and DCA patterns, 

 appeared to be better placed in a different existing TWINSPAN 

 class. These plots were repositioned in the classification as 

 appropriate. 



In addition to helping refine the TWINSPAN classification, 

 DCA ordination assisted in describing and interpreting general 

 patterns of vegetation communities and environment. For example, 

 DCA extracts the dominant compositional gradients from the 

 species data matrix. The environmental controls of these 

 compositional gradients are then interpreted based on comparisons 

 with the site data. 



Taxonomic Considerations 



Nomenclature generally follows Great Plains Flora 

 Association (1986) . Nomenclature for taxa not listed in this 

 manual follows Dorn (1988). Scientific names of all species 

 observed in this study and their code names, number of 

 occurrences, and importance values are listed in Appendix A. 



