PREDICTING SAVANNA VEGETATION STRUCTURE ON THE BASIS OF PLANT-AVAILABLE MOISTURE (PAM) AND PLANT-AVAILABLE NUTRIENTS (PAN) - A CASE-STUDY FROM AUSTRALIA

The use of the plant available moisture (PAM)/plant available nutrient s (PAN) concept to compare savanna structure was examined using data f rom twenty Australian sites. Above-ground biomass was regressed on var ious combinations of seventeen different estimates of PAM (plant avail able moisture) and two estimates of PAN (plant available nutrients). T he ratios of actual transpirational loss from the subsoil to potential evapotranspiration (PET), and total annual rainfall to PET, were most highly correlated with total biomass. Grass biomass is poorly predict ed by PAM on its own, and requires inclusion of woody leaf biomass in the regression. PAN had little effect on total biomass, although it is likely to be important for other, functional aspects of vegetation. T he woody:grass ratio is best predicted by an index involving the ratio of subsoil:topsoil moisture. For biomass comparisons the use of a det ailed water-balance model to estimate PAM is not warranted.