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Ecosystems

, Volume 8, Issue 1, pp 17–32 | Cite as

Tree Canopy Effects on Simulated Water Stress in Southern African Savannas

  • Kelly K. CaylorEmail author
  • Herman H. Shugart
  • Ignacio Rodriguez-Iturbe
Article

Abstract

A coupled energy and water balance model is used to simulate the effects of large tree canopies on soil moisture and water stress across a series of sites spanning a regional moisture gradient in southern Africa. The model tracks evapotranspiration from five components of the land surface at each site—the tree canopy, the grass under and between tree canopies, and the bare soil under and between tree canopies. The soil moisture dynamics are simulated at daily time steps and driven by a stochastic model of storm arrivals and storm depth. Evapotranspiration is modeled using the Priestley-Taylor approach, with potential evapotranspiration scaled by soil moisture availability. The soil moisture under tree canopies is compared to the soil moisture between tree canopies, and differences in average annual soil moisture stress conditions are analyzed at each site. The spatial distribution of large trees has important consequences for small-scale soil moisture dynamics across the rainfall gradient. The results indicate that tree canopies serve to reduce soil moisture stress of under-canopy vegetation in the middle of the rainfall gradient. At the dry end of the rainfall gradient, the effect of tree canopies on soil moisture is dependent on the amount of rainfall received in a given growing season.

Keywords

energy and water balance model tree canopies soil moisture water stress rainfall southern Africa Kalahari Transect 

Notes

Acknowledgments

This study was part of the Southern African Regional Science Initiative (SAFARI 2000) and was conducted within the framework of the IGBP Kalahari Transect. K.K. C.’s research was supported by a NASA Earth System Science Fellowship while at the University of Virginia and by the Clayton Postdoctoral Fellowship at Princeton University. Additional funding was provided through the following NASA grants: NAG5-7956, NAG5-7266, NAG5-7862, and NAG5-9357. I.R.-I. acknowledges the support of the National Science Foundation through the grants in Biocomplexity (DEB-0083566) and the National Center for Earth-surface Dynamics (EAR-0120914). R. J. Scholes, P. R. Dowty, and the late D. A. B. Parsons helped to coordinate and conduct the fieldwork. We gratefully acknowledge the assistance of a number of people at the field sites, including Susan Ringrose (Pandamatenga), Otlogetse Totolo (Tshane), Mukufute Mukelabai (Kataba), Johannes Swanepoel (Sandveld), Evaristo Chileshe (Liangati, Lishuwa), Felix Bainga (Sachinga), Mwenda Mumbuna (Liangati), A. T. Mubone (Lishuwa), Petrus Rust (Vastrap), and the late W. Horn (Vastrap). K. Nomai was very helpful at Lishuwa, and we are grateful for his assistance. Finally, we thank Paolo D‘Odorico, and three anonymous reviewers for their help with early drafts of the manuscript.

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Copyright information

© Springer Science+Business Media, Inc. 2005

Authors and Affiliations

  • Kelly K. Caylor
    • 1
    Email author
  • Herman H. Shugart
    • 2
  • Ignacio Rodriguez-Iturbe
    • 1
  1. 1.Department of Civil and Environmental EngineeringPrinceton UniversityPrincetonUSA
  2. 2.Department of Environmental SciencesUniversity of VirginiaCharlottesvilleUSA

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