Quantifying Climate and Landscape Position Controls on Soil Development in Semiarid Ecosystems

Soils require study across semiarid ecosystems to better understand soil organic C storage and landscape evolution in water-limited environments. The objective of this research was to quantify soil morphologic development in contrasting climate-vegetation zones and landscape positions along a semiarid environmental gradient. Five ecosystems were examined across the Santa Catalina Mountains, Arizona, that exhibit variation in precipitation (45-95 cm yr(-1)), temperature (18-9 degrees C), and vegetation (desert scrub to mixed conifer). Granitic soil, saprock, and parent rock were sampled from divergent summit and convergent footslope positions within each ecosystem. Laser particle size analysis was combined with elemental analysis to determine particle size distribution and total C for all soils. Harden's profile development index was applied to explore changes in soil development with climate and landscape position. Soil organic C increased significantly from 0.37 to 1.1 kg m(-3) in the transition from desert scrub to mixed conifer convergent soils. Silt concentrations also increased significantly between the two convergent field sites, with values increasing from 4.6 to 23 kg m(-3). Profile development indices more than doubled from the desert scrub to mixed conifer sites. At the hillslope scale, indices were similar between desert scrub divergent and convergent landscape positions. However, profile development indices in mixed conifer convergent positions were twofold higher than those of divergent sites, suggesting a stronger topographic control on soil development in these forests. The results demonstrate links between water availability and soil organic C accumulation, both regionally across climate-vegetation zones and locally at the hillslope scale of study.