Predicting the water use of Eucalyptus nitens plantation sites in Tasmania from inventory data, and incorporation of water use into a forest estate model

• Water use was measured in 5 plantations for 3 years, and in a further plantation for 1 year.
• Eucalyptus nitens plantation water use was related to plantation basal area and annual rainfall.
• An existing forest estate model was used to simultaneously predict water use, and wood production.
• This enables forest managers to manage plantation water use in accordance with policies.

The aim of this work was to derive a function predicting annual water use of Eucalyptus nitens plantations from basal area data, and to incorporate this function into an existing forest estate wood-flow scheduling model to allow assessment of the impacts of plantation management simultaneously on wood production and water use.Annual plantation water use was measured in five plots in four adjacent E. nitens plantations 1–11 years after establishment in the Florentine Valley, Tasmania, Australia, over three years from 2008 to 2010, using continuous measurements of transpiration, canopy interception and soil evaporation (the components of plantation water use). Plantation water use ranged from 545 mm yr−1 in a 1-year-old plantation, to 1052 mm yr−1 in an unthinned 9-year-old plantation. Thinning (>50% basal area reduction) reduced plantation water use by around 30%.An empirical model was developed from the Florentine data to predict annual water use of E. nitens plantations from their basal area. This model explained 64% of the variability in water use in the input dataset containing data from both thinned and unthinned plantations. Inclusion of annual rainfall data improved the explanatory power of the model to 78.5% of the variability in water use. The model predicted annual water use of 791 mm for a 6-year-old E. nitens plantation at Forestier, Tasmania in 2011; site water use measured for that year was 792 mm.The basal area:water-use relationship was included in Forestry Tasmania’s existing forest estate model, and used to estimate water use and available wood volume for 1532 ha of E. nitens plantations in the Florentine Valley over a 90-year period and for a range of hypothetical scenarios. Optimised harvesting schedules were produced by incorporating water-use constraints into the forest estate model.