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Research Letters in Ecology
Volume 2007 (2007), Article ID 37364, 5 pages
Research Letter

Is Climate Change a Possible Explanation for Woody Thickening in Arid and Semi-Arid Regions?

Institute for Water and Environmental Resource Management, University of Technology Sydney, P.O. Box 123, 15 Broadway, NSW 2007, Australia

Received 4 October 2007; Accepted 9 December 2007

Academic Editor: Jianguo (Jingle) Wu

Copyright © 2007 Derek Eamus and Anthony R. Palmer. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Increased woody plant density (woody encroachment or woody thickening) is a globally observed phenomenon. Similarly, increased atmospheric carbon dioxide concentrations and decreased pan evaporation rates are globally observed phenomena. In this paper, we propose that the former (increased woody plant density) is a product of the latter. We propose that decreased stomatal conductance and increased rates of carbon fixation arising from an enriched atmospheric carbon dioxide concentration, in conjunction with reduced rates of pan evaporation, result in increased woody plant density. We suggest that this is analogous to the increased woody plant density that is observed along rainfall gradients that span arid to mesic environments. From this conceptual model, we make three predictions, namely, that (a) long-term trends in tree water-use-efficiency should reveal increased values; (b) run-off data should show an increase where woody thickening is occurring; (c) enriched CO2 experiments should reveal an enhanced plant water status. These three predictions are discussed and shown to be supported by experimental data.