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

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Journal Article
Australian Journal Of Botany, 2008, 56 (7), pp. 557 - 563
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Trends in global soil moisture are needed to inform models of soilplantatmosphere interactions. Predawn leaf water potential (?pd), 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 ?pd on LAI relationship. Following an analysis of ?pd and MODIS LAI data from Australian forests, woodlands and savannas, we identified patterns in ?pd 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. ?pd 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 ?pd 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.
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