Large-scale modelling of forest hydrological processes and their long-term effect on water yield

Abstract

Abstract:A water balance model was used to simulate the long-term increases in water yield with forest age which are observed in the mountain ash (Eucalyptus regnans) forests of Victoria, Australia. Speci®cally, the hypothesis was tested that water yield changes could be explained by changes in evapotranspiration resulting from changes in leaf area index (LAI). A curve predicting changes in the total LAI of mountain ash forest was constructed from ground-based observations and their correlation with Landsat Thematic Mapper measurements of the transformed normalized dierence vegetation index (TNDVI). A further curve for mountain ash canopy LAI was constructed from destructive LAI measurements and stem diameter measurements. The curves were incorporated within Macaque, a large-scale, physically based water balance model which was applied to three forested catchments (total area 145 km 2 ). The model was used to evaluate the eect of changes in LAI on predicted stream¯ow over an 82-year period spanning the 1939 wild®res which burnt most of the area. The use of the LAI curves induced improvement in the predicted hydrographs relative to the case for constant LAI, but the change was not large enough to account for all of the dierence in water yield between old-growth and regrowth forests. Of a number of possibilities, concomitant changes in leaf conductance with age were suggested as an additional control on stream¯ow. These were estimated using data on stand sapwood area per unit leaf area and coded into Macaque. The hydrograph predicted using both the LAI curves and a new leaf conductance versus age curve accurately predicted the observed long-term changes in water yield. We conclude that LAI is a partial control on long-term yield changes, but that another`water use eciency per unit LAI' control is also operative.

Retraction notice to 'Impacts of fire on forest age and runoff in mountain ash forests.' [ Functional Plant Biology 35(2008), 483–492. doi:10.1071/FP08120]

“…10). Our result of a 135 mm year À1 reduction in annual ET between 24 and 296 years old is more consistent with Watson et al (1999), who showed that the difference from 25-year-old to pre burn levels was on the order of 150 mm year À1 . These findings provide additional information that can be used to further interpret and refine the relationships suggested by Kuczera.…”

Predicting long‐term streamflow variability in moist eucalypt forests using forest growth models and a sapwood area index

“…Finally, it is worth noting that Kuczera [1987] assumed no increase in streamflow immediately after disturbance, whereas our results support Watson et al [1999] and Bren et al [2010], who empirically show that streamflow in these catchments does increase immediately after disturbance for several years.…”

Catchment hydrological responses to forest harvest amount and spatial pattern

“…Successional changes in forest transpiration are generally consistent with changes in forest Leaf Area Index (LAI), sapwood basal area, and net primary production (NPP) [Watson et al, 1999;Zimmermann et al, 2000]. Ryan et al, [1997] found that forest LAI increases initially after disturbance, reaches a maximum in young stands, and thereafter decreases.…”