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United States Department of Agriculture

Agricultural Research Service

Research Project: HYDROLOGIC PROCESSES, SCALE, CLIMATE VARIABILITY, AND WATER RESOURCES FOR SEMIARID WATERSHED MANAGEMENT

Location: Southwest Watershed Research

Title: Woody plants modulate the temporal dynamics of soil moisture in a semi-arid mesquite savanna

Authors
item Potts, D. - BUFFALO STATE UNIVERSITY
item SCOTT, RUSSELL
item Bayram, S. - BUFFALO STATE UNIVERSITY
item Carbonara, J. - BUFFALO STATE UNIVERSITY

Submitted to: Ecohydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 26, 2009
Publication Date: March 8, 2010
Citation: Potts, D.L., Scott, R.L., Bayram, S., Carbonara, J. 2010. Woody plants modulate the temporal dynamics of soil moisture in a semi-arid mesquite savanna. Ecohydrology. 3:20-27.

Interpretive Summary: Because water is so important to life on this planet, knowing the amount of moisture in the soil is important for predicting the response of plants in natural ecosystems to events such as global warming, increases in atmospheric carbon dioxide, and changing land-use patterns. Dry lands worldwide are currently experiencing an increase in the density and cover of woody plants. Whatever the cause, woody plants influence the spatial and temporal availability of soil moisture with potentially important effects on local and regional hydrologic cycling. We monitored soil moisture at a semiarid savanna near Tucson, AZ to determine the effect that the trees had on the amount of soil moisture in the soil. We found that the tree canopy reduced the amount of precipitation input into the soil, but also that the shade of the canopy had the tendency to reduce evaporative losses so that the soil dried less quickly than soil out in the open. These findings are consistent with, and may help to explain, the results of other investigations that have examined the role of woody plants in enhancing nutrient cycling and altering carbon cycling in dryland ecosystems.

Technical Abstract: In arid and semi-arid ecosystems (drylands), soil moisture abundance limits biological activity and mediates the effects of anthropogenic global change factors such as atmospheric CO2 increases and climate warming. Moreover, climate variability and human activities are interacting to increase the abundance of woody plants in drylands worldwide. How woody plants interact with rainfall to influence patterns of soil moisture through time, at different depths in the soil profile and between neighboring landscape patches is poorly known. In a semi-arid mesquite savanna near Tucson, Arizona we deployed arrays of sensors located in distinct microsites (beneath a mesquite canopy and in an open area) to measure volumetric soil water content (') every 30 minutes at several depths between 2004 and 2007. In addition, to quantify temporally dynamic variation in soil moisture between microsites and across soil depths we analyzed ' time-series using Fast Fourier Transforms (FFT). FFT analyses confirmed the prediction that by reducing evaporative losses through shade and reducing rainfall inputs through canopy interception of small rainfall events, the mesquite canopy was associated with a decline in high frequency (hour-to-hour and day-to-day) variation in shallow '. Finally, we found that in both microsites, high frequency ' variation declined with increasing soil depth as the influence of evaporative losses and inputs associated with smaller rainfall events declined. These findings are consistent with, and may help to explain, the results of other investigations that have examined the role of woody plants in enhancing nutrient cycling and altering carbon cycling in dryland ecosystems.

Last Modified: 8/19/2014
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