Land area (Mha) of 4 GRDC agro-ecological zones divided by 500 mm mean annual rainfall (MAR) isohyet
GRDC agro-ecological zone <500 mm MAR >500 mm MAR NSW-Vic.
Annual mean values are less than 1600 mm in the entire drainage basin, and average rainfall calculated from the map of isohyets
(Daveau 1971b) is 818 mm.
He mapped centers of diversity using numbers of species in isohyets
6[degrees]E, and between the 300 and 400 mm mean annual rainfall isohyets
with soils that are typically texture contrast (duplex) soils of sand or loams over clay (Chromosols and Sodosols) and sands over gravels (Ferric Chromosols) (Isbell 1996; Schoknecht 2002).
Nevertheless, the available data suggests that the features are most strongly developed between the rainfall isohyets
of 250 and 400 mm (FIGURE 1).