Management of many arid and semi-arid ecosystems has resulted in highly altered community structure, greatly affecting resource availability and community function. Principal among these changes are alterations in the dynamics and function of soil moisture, which has considerably affected interactions among plant species and individuals. This study assesses differences in soil water dynamics within four semi-arid communities of the western USA dominated by different life forms in a top-recharged system: cheat grass (Bromus tectorum), crested wheatgrass (Agropyron desertorum), big sagebrush (Artemisia tridentata) and Utah juniper (Juniperus osteosperma) to assess how individual species would affect the ecohydrology and interactions with other plant species. Soil moisture dynamics were quantified by continuously measuring soil matric potentials at nine depths (0.3 to 3.0 m) using screen-cage thermocouple psychrometers.

Results/Conclusions

Temporal and vertical patterns of water use varied greatly among the four communities, and related in part to differences in plant phenology, root distribution, and hydraulic redistribution of soil and rain water by roots. Important differences were found in the timing and quantity of water use, interception of precipitation as it moved through the soil, patterns of hydraulic redistribution, and potential for interactions among different species and life forms. Variability in water use and soil water dynamics provide strong support for the use of soil water pools as a unifying concept for assessing interactions of plants in water limited ecosystems. Resource pool dynamics can provide both conceptual models and quantitative tools for assessing mechanisms linked to vegetation potential, dynamics and interactions, and provide a mechanism for evaluating changes in site potential. It also highlights the importance of ecohydrology as an important discipline in assessing plant community dynamics and interactions between plant species and individuals.