Water yield from Melbourne’s catchments is currently calculated
using small-scale (e.g., Topog for up to 10 km2) and largescale
(e.g., Macaque for up to 1000 km2) models (Vertessy et al.,
1998) that utilize stand water use measurements derived from sap
flow methods. These models have proven useful, but do not
adequately represent stand water use behavior in response to
seasonal variation in climatic conditions, and have limited capacity
to incorporate water use by the understorey, despite its significance
to total forest water use (Wood et al., 2008). The open canopy
of aging E. regnans forests frequently encourages a substantial midstorey
stratum, commonly comprised mainly of Acacia spp. (A.
dealbata Link. and A. melanoxylon R. Br. Ex Ait. f.), and such species
are likely to make a significant contribution to whole-stand water
use (Dunn and Connor, 1993; Vertessy et al., 1995).