Spatial patterns of dry matter, nitrogen, and organic carbon were investigated for velvet mesquite [Prosopis juliflora (Swartz)] DC and for palo verde [Cercidium floridum Benth.] ecosystems in the Upper Sonoran Desert of Arizona. Standing understory vegetation and litter originating from the overstory shrub decreased in weight as distance from the shrub center increased. Litter originating from understory vegetation displayed weak spatial patterns in dry weight. Gradients in percentage N and percentage carbon of understory vegetation, understory litter, and shrub litter were generally lacking. However, percentage soil N and organic carbon decreased as horizontal distance from the shrub center and depth to 60 cm from the surface layer increased; soil pH under both shrubs changed with depth and horizontal distance. Quadratic response surfaces for these three soil properties differed significantly between velvet mesquite and palo verde. Limited sampling of honey mesquite (Prosopis juliflora var glanulosa Torr.) ecosystems in the Chichuahuan Desert in New Mexico showed spatial patterns of dry matter and soil properties that differed somewhat from those of Sonoran Desert shrubs.

Over a 3-year period, soil-plant systems of velvet mesquite and palo Verde from the Sonoran Desert were sampled by standing crop, litter, and soil components and analyzed to describe the amount and distribution of dry matter, nitrogen, and carbon in the systems. Honey mesquite was sampled on a limited basis in southern New Mexico. Velvet mesquite averaged about one-third larger in crown area and weight than palo Verde, but the two shrubs were similar in the distribution of dry matter, N, and C. Honey mesquite was much smaller and differed in distribution of dry matter, N, and C. Regression analysis showed that dry matter, N, and1 C in components of shrub systems of velvet mesquite and palo Verde varied in a predictable manner and can be estimated with good precision using height, average crown diameter, or crown area of shrubs as the independent variable. Functional analysis showed that soil under palo-Verde did not accumulate N or C-with increase lin shrub size, whereas that under velvet mesquite accumulated N :at the rate of 11.2 g/m* per meter of height and C at the rate of 0.11 kg/m* per meter of height. Shrubs dominate the vegetation on over 200 millialn hectares of land in the conterminous United States, mostly in the Southwest and the Intermountain Basin. Many authorities consider shrubs the climax vegetation on about one-half this area, while on the remaining 1'00 million hectares shrubs now dominate where grasses were once the climax dominants. Man has been using shrublands since prehistoric times, but until recently little management has been applied. When used, management usually has been directed at eliminating shrubs. Because shrubs play an important role in terrestrial ecosystems, we should understand their ecological role. This is especially important in arid areas where shrubs are an important component of the vegetation. This paper reports on a study to determine how dry matter, nitrogen, and carbon were accumulated and distributed in soil-plant systems of two desert shrubs: velvet mesquite (Prosopis juliflora) and palo verde (Cerdicium floridurn). Limited data on honey mesquite (Prosopis juliflora var. glandulosa) are included as an adjunct to the main study. Methods Study Locations The study area was located in the Upper Sonoran Desert approximately 32 km south of Tucson, Arizona, at the Santa Rita Experimental Range. The study site was on an alluvial plain with a slope of less than 5% and an elevation of 975 m. Numerous arroyos and small shallow washes dissect the upland areas. Sampling was conducted on the upland sites on the Sonoita soil series, a coarse, loamy, mixed, thermic family of Typic Haplargids derived from The authors are senior research ecologist,

The synthesis of the new ligand (C6H5)2PCH2OP(C6H5)2 is reported. Coordination compounds of this ligand and its analog (C6Hs)2PCH2CH2OP(C6H5)2 with chromium, molybdenum, and tungsten carbonyls and with PdCl2 are reported with 31P and • nmr data, including phosphorus-phosphorus and phosphorus-tungsten coupling constants where appropriate. Phosphorus nmr data are also reported for (C6Hs)2P(CH2)nP(C6H5)2M(CO)4, where M = Cr, Mo, or W and n-1,2, or 3. An unusually large downfield phosphorus coordination shift is observed in the case of all five-membered chelate rings, which is not observed in the case of the fourand six-membered chelate rings.

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The objective of this study was to determine depth of soil that should be applied over spoil to ensure adequate production of cool‐season grasses at surface mines in the Northern Great Plains. During a 6‐yr period, data were collected from 15 wedge plots and the response of perennial grass production to increasing soil depth was measured. Production responses were dependent on spoil traits and four spoil types were recognized: generic, sodic, acid, and soil‐like. Soil depth required for maximum production was 50 cm for generic spoil, 71 cm for sodic spoil, indeterminate for acid spoil, and 0 cm for soil‐like spoil. Root penetration into spoil appeared limited to ≤ 10 cm, except for soil‐like spoil where root penetration exceeded 110 cm. Native and introduced grasses responded in a similar manner to increasing soil depth, and precipitation had no significant effect on the depth of soil required for maximum grass production.