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Title: Hydrologic response to precipitation pulses under and between shrubs in the Chihuahuan Desert, Arizona

Author
item Moran, Mary
item Hamerlynck, Erik
item Scott, Russell - Russ
item Keefer, Timothy
item DEYOUNG, L. - University Of Arizona
item NEARING, G. - University Of Arizona
item SUGG, Z. - University Of Arizona
item HYMER, D. - National Aeronautics And Space Administration (NASA)

Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/21/2010
Publication Date: 10/8/2010
Citation: Moran, M.S., Hamerlynck, E.P., Scott, R.L., Keefer, T.O., Bryant, R.B., Deyoung, L., Nearing, G.S., Sugg, Z., Hymer, D.C. 2010. Hydrologic response to precipitation pulses under and between shrubs in the Chihuahuan Desert, Arizona. Water Resources Research. 46: W10509. doi:10.1029/2009WR008842.

Interpretive Summary: In desert ecosystems, infrequent storms are the key drivers of plant growth and reproduction. It follows that the areas best able to capture and retain soil water are also most conducive to vegetation establishment and stability. In this way, the distribution of water from discrete storms can determine the vegetation species composition and distribution in arid and semiarid ecosystems. The objectives of this analysis were to study the impact of storms on the soil moisture under and between shrubs, related to observed vegetation patterns. Results showed that the root-zone soil moisture was about 20% lower under shrubs than between shrubs across all storms over a 20-year period. We concluded that the greater root density under shrubs may decrease under-shrub soil moisture. This result provides new insight into the potential for vegetation change in arid and semiarid lands. The study has particular relevance to changes in vegetation distribution associated with changing climate because climate models predict higher variability in the size and frequency of storm events with increasing Earth temperature.

Technical Abstract: Observations of the temporal and spatial distribution of post-storm soil moisture in open shrublands and savannas are limited, yet they are critical to understanding the interaction and feedbacks between moisture distribution and canopies. The objectives of this analysis were to study the hydrologic impacts of precipitation pulses on the upper layer of soils under and between shrubs. The study was based on measurements of precipitation, runoff and under- and between-shrub soil moisture over a period of 20 years (1990-2009) at a shrub-dominated site in the Walnut Gulch Experimental Watershed (WGEW) near Tombstone, Arizona. Within much of the root-zone (to 30-cm depth), infiltration was not significantly different under versus between shrubs, and the under:between infiltration ratio was not related to pulse size or intensity. Yet, root-zone soil moisture was significantly higher between shrubs than under shrubs. The soil moisture measured at the surface (at 5-cm depth) was not significantly different under and between shrubs, but the soil moisture measured at depths of 15-cm and 30-cm were both higher between shrubs than under shrubs. Considering mechanisms that explain the interaction between plants and soil moisture, we found no differences in infiltration capacity, evaporative losses, and surface soil moisture in locations under and between shrubs. This led to the conclusion that lower root-zone soil moisture under shrubs was due largely to greater root density under shrubs than between shrubs. This study adds to the understanding of the impact of precipitation patterns on infiltration and soil moisture in shrub-dominated sites and the potential for vegetation change in arid and semiarid lands.