Controls on ecohydrologic properties in cold desert ecosystems: Differences in soil age and volcanic morphology
Research on the influence of parent material on soil development is limited in semi-arid environments. In volcanic soils, most studies examining the influence of soil development with time have been conducted in humid environments, where weathering occurs rapidly. This study was conducted in a semi-arid environment to examine the influence of volcanic parent material type and the age of that material on key soil hydraulic properties that may be important predictors of primary succession, especially in the context of extreme drought. Four study sites were selected across young (~2.0 ka) and old (~12.1-13.9 ka) end members of two different parent materials (cinder cones and pahoehoe lava flows). We hypothesized that soils and associated hydraulic properties would evolve more rapidly on the cinder cone compared to the pahoehoe flows owing to greater exposed surface area on the cinder. For each site, we quantified vegetation cover and a range of edaphic soil properties including soil organic matter, bulk density, water characteristic curves, and hydraulic conductivity.
Larger differences in saturated hydraulic conductivity and soil-water retention data at the cinder compared to the pahoehoe sites supported the hypothesis that soils on cinder cone material evolved more rapidly than pahoehoe material. Laboratory texture measurements showed that the older cinder cone soils had a substantial sand fraction that was likely eolian sourced. The older pahoehoe site remained dominated by unweathered basalt, and desert shrubs established in cracks and crevices, where silty eolian material accumulated. Plant communities on cinder cone may be more resilient to extreme droughts than those on pahoeohoe materials because soils, and consequently primary succession and landscape development, evolve more rapidly and support water retention functions and more plant-available water storage. This resilience in turn promotes primary succession and landscape development.