The use of pre-dawn leaf water potential and MODIS LAI to explore seasonal trends in the phenology of Australian and southern African woodlands and savannas
Anthony R. Palmer A C , Sigfredo Fuentes A , Daniel Taylor A , Cate Macinnis-Ng A , Melanie Zeppel A , Isa Yunusa A , Edmund February B and Derek Eamus AA Institute for Water and Environmental Resource Management, University of Technology Sydney, PO Box 123, Broadway, NSW 2007, Australia.
B Department of Botany, University of Cape Town, Private Bag, Rondebosch 7701, South Africa.
C Corresponding author. Email: anthony.palmer@uts.edu.au
Australian Journal of Botany 56(7) 557-563 https://doi.org/10.1071/BT08079
Submitted: 7 May 2008 Accepted: 1 September 2008 Published: 26 November 2008
Abstract
Trends in global soil moisture are needed to inform models of soil–plant–atmosphere interactions. Predawn leaf water potential (Ψpd), a surrogate for soil moisture and an index of plant water stress, has been routinely collected in Australian forests, woodlands and savannas, but the associated leaf area index (LAI) has seldom been available to enable the preparation of a Ψpd on LAI relationship. Following an analysis of Ψpd and MODIS LAI data from Australian forests, woodlands and savannas, we identified patterns in Ψpd which provide an understanding of the role of soil-moisture status in controlling LAI. In the savanna of northern Australia, the MODIS LAI product had a basal value of 0.96 during the dry season as compared with a mean value of 2.5 for the wet season. The dry season value is equivalent to the LAI of the tree component and corresponds with ground-truthed LAI. Ψpd is lowest (more negative) during the height of the dry season (late October) at −2.5 MPa, and highest (−0.1 MPa) during the wet season (early March). We present two models which predict Ψpd from the MODIS LAI product. These may be useful surrogates for studying trends in soil moisture in highly seasonal climates and may contribute to climate change research.
Acknowledgements
We acknowledge the assistance of Tony O’Grady and Craig Macfarlane for providing some of the original LAI and Ψpd data for Western Australia and the Northern Territory. Funding for the research in South Africa was made available from a grant by the Mellon Foundation of New York.
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