December 2012 Number 1 - Utah Native Plant Society

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Utah Native Plant Society Table 1. continued Scientific Name Family >1 m tall? # Sites w/sp a CL02 cl % of Subplots Occupied in Each Site b CL02 un CL07 cl CL07 un AM07 AR03 SM04 Unidentified cactus seedling Cactaceae 1 - - - - - - 0.67 Unknown grass Poaceae 5 8.00 0.81 25.93 24.44 21.03 11.18 1.33 Unknown legume Fabaceae 1 - - - 0.74 - - - Unknown 1 1 1.60 - - - - - - Unknown 2 2 3.20 2.42 0.74 1.48 - - - Unknown 3 1 1.60 - - - - - - Unknown 4 1 0.80 - - - - - - Unknown 5 5 2.40 1.61 4.44 7.41 0.69 5.29 0.67 Unknown 6 1 - - - - - - 1.33 Unknown 7 1 - - - - - 1.76 - Urochloa ciliatissima Poaceae 1 - - - - 1.03 - - Urochloa texana Poaceae 1 - - 0.74 - - - - Verbena sp 1. Verbenaceae 2 - - 2.22 - 2.76 - - Verbena sp 2. Verbenaceae 3 - - 2.22 0.74 1.72 - - Wedelia texana (A. Gray) B.L. Turner Asteraceae 5 2.40 - 19.26 0.74 4.48 0.59 0.67 Yucca treculeana Agavaceae X 2 - - - 0.74 0.34 - - Zanthoxylum fagara Rutaceae X 1 - - - - 1.03 - - Ziziphus obtusifolia Rhamnaceae 4 - - 0.74 - 0.69 0.59 0.67 Bare ground (no plants in subplot) 5 0.80 7.26 - - 0.34 4.12 3.33 a Number of sites with this species: Cuellar cleared and uncleared counted as different ‘sites’ due to treatment difference b Site codes: CL cl = Cuellar cleared; CL un = Cuellar uncleared; AM = Arroyo Morteros; AR = Arroyo Ramirez; SM = Santa Margarita. Numbers 02-07 refer to year of vegetation data collection. 182
Calochortiana December 2012 Number 1 RESULTS Differences in Vegetation Among Sites A total of 150 vascular plant species occurred in at least one vegetation plot in a least one site (Table 1). Sixty-six of these species occurred in only one of the four sites (pooling Cuellar treatments). While the vegetation of the four sites was similar in many ways, the relative abundances of species differed among sites (Table 1). In Arroyo Morteros, Thymophylla pentachaeta, Acacia rigidula, and Chaetopappa bellioides/ Aphanostephus skirrhobasis var. kidderi were most abundant; in Arroyo Ramirez, Aristida purpurea, Turnera diffusa, Acacia rigidula, and Polygala lindheimeri; in Santa Margarita, Aristida purpurea and Eriogonum greggii; and in Cuellar, Acacia rigidula, Leucophyllum frutescens, Polygala lindheimeri, and Melampodium cinereum. Sites also differed in the abundances of less common species (Table 1). A MANOVA (multivariate analysis of variance) comparing the abundances of all species (except P. thamnophila and ‘bare ground’, for a total of 146 ‘species’ after the pooling described in the Methods) among the five site x treatment combinations (Cuellar treatments not pooled) was highly significant (Cuellar 2007 vegetation data used; Hotelling-Lawley Trace, F = 9.44, df = 548, 114.71, P < 0.0001). The four sites also differed in vegetation structure (Figure 5). The lack of vegetation above 1m in the cleared portion of Cuellar in 2002 was due to its treatment, while the uncleared portion of Cuellar had the densest canopies. The regrowth in the Cuellar cleared portion is apparent in a comparison of the 2002 and 2007 graphs (Figure 5). Among uncleared sites, Arroyo Ramirez had the most open canopies, and Arroyo Morteros the tallest. Relationships Between P. thamnophila Presence and Neighboring Species Twenty-nine species, including P. thamnophila, were present in 25 percent or more of the subplots. These species, except for P. thamnophila, were used as the dependent variables in a MANOVA. In this MANOVA, site and P. thamnophila presence/absence in the 2007 census were the independent variables. Cuellar 2007 vegetation data were used in this analysis and the two Cuellar treatments were considered to be 2 different ‘sites’, for a total of 5 site-treatment combinations. Both of the independent variables were highly significant (site-treatment combination: Hotelling-Lawley Trace F = 20.67; df = 112,476; P < 0.0001; presence/absence: Hotelling-Lawley Trace F = 1.93; df = 28,143; P = 0.0066). Because the MANOVA found significant effects of P. thamnophila presence we followed it with ANOVAs (univariate analyses of variance). Six of 28 ANOVAs on the same 28 species had P-values less than 0.05 associated with the effect of P. thamnophila presence/absence. In each of these ANOVAs, presence/absence, df = 1, was the second factor in a hierarchical sums of squares table that had site, df = 3, as the first factor. Thus these P-values reflect the amount of variation that presence/ absence accounted for above-and-beyond the variation accounted for by site-year combination. Plots that had P. thamnophila had on average more Diospyros texana (P = 0.0424), Acacia rigidula (P = 0.0043), unidentified seedling grasses (P = 0.0068), Mimosa texana (P = 0.0012), and Chamaesaracha sordida + Physalis cinerascens (P = 0.0293), and less Tiquilia canescens (P = 0.0293), than plots without P. thamnophila. These positive and negative associations with P. thamnophila should be regarded as tentative, due to multiple testing issues, deviations from the multivariate normal assumption, and correlations among abundances of the different species. Only Mimosa texana meets the Bonferroni criterion for significance (for 28 tests, P < 0.00183 to give an overall P < 0.05). Relationships Between P. thamnophila Density and Neighboring Species A stepwise regression was used (SAS PROC REG) with the average 2006/2007 density of P. thamnophila as the dependent variable. Site was included as a class variable (df = 3). All 148 ‘species’ except bare ground and P. thamnophila were available to the regression procedure. A criterion of P < 0.05 was used to retain variables in the model. Eighteen taxa met this criterion. Thirteen of them were negatively associated with P. thamnophila: Acleisanthes obtusa, Acourtia runcinata, Citharexylum brachyanthum, Thymophylla pentachaeta, Echinocactus texensis, Echinocereus reichenbachii ssp. fitchii, Galphimia angustifolia, Nama hispidum, Oenothera laciniata, Portulaca sp., Sideroxylon celastrinum, Synthlipsis greggii, and Tridens muticus. Five were positively associated with P. thamnophila: Acacia rigidula, Cyperus sp., Evolvulus alsinoides, Melampodium cinereum, and Passiflora tenuiloba. DISCUSSION Community Composition: General Each of the study sites had a rich plant community that contained shrubs, forbs, graminoids, and cacti (Table 1). The shrubs Acacia rigidula and Leucophyllum frutescens dominated all four sites. While all four study sites were similar enough to be described as having the same plant community, there were some interesting differences among them. These include Turnera diffusa, found in 59 percent of samples at Arroyo Ramirez but absent from other sites; Eriogonum greggii, itself a 183
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December 2012 Number 1 - Utah Native Plant Society

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