THE AUTHORS 



E. DURANT McARTHUR is Project Leader and re- 

 search geneticist for the Shrubland Biology and Restora- 

 tion Research Work Unit at the Intermountain Research 

 Station's Shrub Sciences Laboratory at Prove, UT. His 

 degrees are from Dixie College, St. George, UT (A.S. 

 in physical sciences, 1963) and the University of Utah 

 (B.S. in molecular and genetic biology, 1965; and M.S., 

 1967, and Ph.D., 1970, in plant genetics). He was a 

 postdoctoral research fellow in agricultural botany for 

 the Agricultural Research Council of Great Britain at the 

 University of Leeds during 1970 and 1971. He began 

 his Forest Service research career at the Great Basin 

 Experimental Range at Ephraim, UT, in 1972. He has 

 been at the Shrub Sciences Laboratory in Prove, UT, 

 since 1975 and has been Project Leader since 1983. He 

 has held appointments as adjunct professor of botany 

 and range science at Brigham Young University since 

 1976. 



STEWART C. SANDERSON is research geneticist for 

 the Shrubland Biology and Restoration Research Work 

 Unit at the Intermountain Research Station's Shrub 

 Sciences Laboratory at Provo, UT, and research associ- 

 ate in the Department of Botany and Range Science, 

 Brigham Young University, Provo, UT. His degrees are 

 from Brigham Young University (B.S., 1967, and M.S., 

 1969, in botany) and the University of Texas at Austin 

 (Ph.D. in botany, 1975). He was postdoctoral research 

 fellow at the University of Durham, United Kingdom, dur- 

 ing 1975 and 1976. He has held appointments at the 

 Shrub Sciences Laboratory since 1981 and at Brigham 

 Young University since 1976. 



BRUCE L. WEBB is director of the Soil and Plant Analy- 

 sis Laboratory, Brigham Young University, Provo, UT, 

 an appointment he has held since 1973. His degrees 

 are from Brigham Young University (B.S., 1972, in 

 agronomy with a chemistry minor and M.S., 1978, in 

 agronomy with a statistics minor). He worked for the 

 U.S. Department of Agriculture, Soil Conservation Ser- 

 vice as a soil conservationist in Monticello, UT, from 

 1972 to 1973. 



RESEARCH SUMMARY 



Grasses, forbs, shrubs, and succulents (cacti) that 

 desert tortoises {Gopherus agassizii) might eat were 



analyzed over the spring, summer, and fall seasons at 

 two study areas in southwestern Utah (City Creek near 

 St. George and Woodbury-Hardy on the Beaver Dam 

 Slope) and at one site in northwestern Arizona (near 

 Littlefield). Earlier researchers suggested that tortoises 

 were healthier at City Creek than at the other areas, es- 

 pecially Woodbury-Hardy. 



Plant materials were analyzed for moisture content, ni- 

 trogen (total organic nitrogen; crude protein = 6.25 x total 

 organic nitrogen), phosphorus, potassium, zinc, iron, 

 manganese, copper, calcium, magnesium, sulfur, sodium, 

 ADF (acid detergent fiber), TNC (total nonstructural car- 

 bohydrates), and crude fat (ether extract) for a 3-year 

 period (1989-91). Plants from the three areas had simi- 

 lar values for most nutrients and minerals, but Littlefield 

 plants had significantly (P< 0.05) higher values for po- 

 tassium, copper, and fat. Some nutrition and mineral 

 parameters were different for the six plant classes, an- 

 nual and perennial grasses, annual and perennial forbs, 

 shrubs, and succulents. 



In general, when differences existed, annual forbs were 

 higher in mineral and nutrient content than other plant 

 classes. Plants with high moisture content were high for 

 other measured parameters. Various parameters were 

 correlated; potassium and nitrogen were highly corre- 

 lated with the other variables. Plant mineral values did 

 not generally track soil mineral values. Values of miner- 

 als and nutrients for both plants and soils fell in normal 

 ranges for semiarid conditions; however, sodium was 

 low for both soils and plants. Low sodium concentra- 

 tions may contribute to health problems for desert tor- 

 toises. The mineral and nutrient content of cow excre- 

 ment does not appear to make it a quality food source 

 for desert tortoises as has been recently suggested. 



ACKNOWLEDGMENTS 



This work was made possible, in part, by financial sup- 

 port from the Cedar City and Arizona Strip Districts of 

 the Department of the Interior, Bureau of Land Manage- 

 ment (Interagency Agreement UT-910-IA9-787). Todd 

 Esque and Lesley DeFaIco provided the plant samples 

 of appendix A. We thank Hal Avery, Scott Belfit, Timothy 

 Duck, Todd Esque, Jerran Flinders, John Payne, Scott 

 Walker, and Bruce Welch for assistance and counsel or 

 review of earlier versions of the manuscript. Lesley 

 DeFaIco drew the desert tortoise on the cover. 



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