Table 12 — Comparison of plant and soil values for various parameters for each study area 



Soil parameter 



Units 



City Creek 



Woodbury-Hardy 



Littlefield 



Soil 



Plant 



Soil 



Plant 



Soil 



Plant 



Calcium 



ppm 



122 



11,800 



132 



14.300 



151 



15,500 



Magnesium 



ppm 



19 



3,100 



14 



4,000 



17 



4,900 



Sodium 



ppm 



4.6 



100 



2.2 



100 



3.3 



120 



Nitrogen 



ppm 



453 



15,500 



475 



14.800 



183 



17,300 



Phosphorus 



ppm 



11.1 



1,300 



10.9 



1,000 



4.7 



1,300 



Potassium 



ppm 



104 



12.900 



130 



13,600 



103 



17,300 



Zinc 



ppm 



0.527 



15 



0.520 



16 



0.333 



18 



Copper 



ppm 



0.663 



6 



0.500 



6 



0.453 



7 



PH 





6.8 





7.5 





7.5 





EC^ 



ds/L 



0.695 





0.465 





0.523 





SAR2 





0.112 





0.052 





0.073 





^Electroconductivity. 

 ^Sodium adsorption ratio. 



Woodbury-Hardy. The slightly elevated values for 

 Littlefield may relate to slightly better weather con- 

 ditions (see next section) during the period of study. 

 Soil mineral content is not higher at Littlefield 

 (table 12). In fact, soil characteristics measured in 

 our study are quite similar among the areas; when 

 City Creek is compared to the other areas, it is high 

 in sodium and SAR but low in pH; City Creek and 

 Woodbury-Hardy are high in nitrogen. Our 3-year 

 study could not support the hypothesis that nutrient 

 and mineral content were more favorable for the ap- 

 parently healthier desert tortoise subpopulation at 

 City Creek. 



Weather and Water 



The higher nutrient and mineral values for Littlefield 

 may well be associated with a higher moisture content 

 (table 2). Moisture input at our study sites is sporadic, 

 in common with the Mojave environment in general 

 (McArthur and Sanderson 1992a). No data are avail- 

 able to document that the Littlefield area received more 

 moisture than the others; however, more sampling was 

 associated vnth arroyos there and at Woodbury-Hardy 

 than at City Creek. Sporadic storms could have favored 

 Littlefield over the other areas. Both Woodbury-Hardy 

 and Littlefield are on the Beaver Dam Slope. Figure 3 

 shows that, during the study period, the Lytle Ranch 

 climatic station on Beaver Dam Wash had a more fa- 

 vorable moisture regime than did the St. George cli- 

 matic station near City Creek. 



Plants with higher moisture content were also higher 

 in nutritive quality and mineral content on a dry- 

 weight basis when all plants were considered (table 7), 

 when annuals were considered (table 9), and when 

 just Bromus ruhens was considered (table 10). Quality 



Precipitation 



1 2 3 4 5 6 

 St. George 1988-91 



1 2 3 4 5 6 

 Lyiie Ranch 1988-91 



Figure 3 — Average values of precipita- 

 tion and maximum daily temperature 

 for St. George and the seasonal aver- 

 age values for those parameters for 

 St. George and Lytle Ranch during 

 the study period. Number 1 = October- 

 March 1988-89, 2 = April-September 

 1989, 3 = October- Inarch 1989-90, 4 = 

 April-September 1 990, 5 = October- 

 March 1990-91, 6 = April-September 

 1 991 . Data for Lytle Ranch were not 

 collected for period 1 . 



11 



