04631nam a2200277 a 450000100080000000500110000800800410001910000270006024500670008726000160015430000110017050000780018152038840025965000120414365000190415565000190417465000130419365000130420665000130421965000110423265000130424365000230425665300250427965300250430465300240432915158652019-10-14       1975    bl uuuu  m   00u1 u    #d1 aARAUJO FILHO, J. A. de  aCharacterization of range sites in the Empire valley, Arizona.  a1975.c1975  a108 f.  aDissertation (Doctor of Philosophy) - The University of Arizona, Arizona.  aAbstract: This research deals with the characterisation of range sites in the Empire Valley study area, 40 miles southeast of Tucson, Arizona. Black and white aerial photographs were used in the reconnaissance, stratification and selection of 304 stands evaluated during 1973 and 1974. Field data collected by occular reconnaissance from each stand included a list of species, dominance and composition ratings of indi­vidual species in herbaceous, shrub, and tree layers, percentage cover of the vegetation layers, cobbles and gravel, soil series, topographical position, slope percent and aspect, and present grazing intensity. Stands were classified into three major categories based on topographical position and limyness of the soil: bottomlands, nonlimy uplands, and limy uplands. Specific plant communities and gravel cover on the soil surface were used to separate tentative sites on the bottom­lands. Solar radiation at the soil surface as affected by slope angle and aspect, slope percent, and cobble cover were used to separate the tentative sites of both the nonlimy and the limy uplands. Multiple re­gression analyses between the abiotic site factors, as independent site varidjles, and individual plant species importance values, as dependent variables, were used to test the influence of the abiotic environmental factors on the occurrence of plant species in the study area. Cluster analyses based on coefficients of similarity among stands were conducted, and groups of stands of similar vegetation composition were identified Correlations among plant species were tested and possible range site con­dition and site potential interactions were discussed. Four tentative sites identified on the bottomlands were justified. Sites 1 and 4 were separated on the basis of specific plant communities, dominated by Hilaria mutica and Sporobolus wrightii and/or tree-size Prosopis juliflora, respectively. Sites 2 and 3, separated on the basis of gravel cover, reflect the differences between Comoro and Pima soil series in terms of vegetation cover. The vegetation groups associated with these latter two sites were greatly influenced by range condition. The ten tentative sites of the nonlimy uplands were regrouped into seven range sites. Site 6, representing the steep south slopes, was justified in terms of characteristic plant species, radiation, and slope. Tentative sites 8 and 11, initially separated in terms of the difference in cobble content, were combined into a single range site because the effects of the differences in range condition obscured the differences caused by the small cobble cover percent. Tentative site 10, repre­senting the flat uplands with fine textured soils, was justified as a range site and supported a specific plant community dominated by Hilaria mutica. Tentative sites 13 and 15, the gentle and moderate slopes of the 600-700 langleys/day radiation class did not present sufficient plant community differences to justify a separation into two distinct range sites. Site 17, representing the steep slopes of the 600-700 langleys/day radiation class was separated as a distinct range site based on dif­ferences in slope and plant community. Two distinct range sites were identified in the low radiation classes in terms of characteristic plant communities. Sites 19 and 22, radiation classes 500-600 and 400-500 langleys/day, respectively, were combined as one site. Site 24, radiation class 300-400 langleys/day, was justified as a distinct range site separated from other north slopes because of steep slope, low herbaceous cover, and presence or absence of specific species. No attempt was made to separate sites on the liny uplands, due to the inadequate number of samples per tentative sites. However, trends indicate a pattern in the number and characteristics of range sites similar to those of the nonlimy uplands.  aEcology  aForage grasses  aHilaria mutica  aPastures  aAlgaroba  aEcologia  aManejo  aPastagem  aProsopis Juliflora  aGrassland management  aIndigenous organisms  aSporobolus wrightii