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Predicting annual plantation water use

Forestry Tasmania is developing a planning tool that will predict changes in the annual water use of plantations.  Forestry Tasmania already has a planning tool called Woodstock for management of wood production from the forest estate. 

Woodstock uses information about forest type, extent, age, management regimes, management constraints, growth rates, forest inventory and site quality to schedule the availability of wood into the future.  With some effort, Woodstock can be adapted to also predict changes in plantation water use.

Woodstock uses the basal area of plantation stands as part of the wood planning process.  Sapwood area and leaf area can be estimated from basal area if we have some knowledge of diameter distribution and site quality.  Previous research also shows that there are strong linkages between stand sapwood area, leaf area and water use. To allow the prediction of plantation water use with Woodstock, we are identifying relationships between the basal area of Eucalyptus nitens plantations and their water use.

Water use is being measured at a E. nitens plantation chronosequence in the Florentine Valley, along with leaf area, sapwood area, stem diameter (basal area), and site quality (rainfall, soils, landscape position) for a representative sample of the plantation estate.  We are also testing existing plantation growth and water use process models to see if they can help us understand the relationships between plantation basal area, sapwood area, leaf area and water use in a range of environments.  Once methods are developed for E. nitens, other plantation species will be studied and included in Woodstock.

The research plots in four plantations in the Florentine Valley are aged 1, 3, 7 and 9 years.  The 9-year-old plantation has both thinned and unthinned plots.  Heatpulsers measure transpiration, throughfall troughs and stemflow collectors calculate canopy interception, and small weighing lysimeters measure soil evaporation.  An automatic weather station and soil moisture sensors have also been installed and regular measurements are made of leaf area, sapwood area, diameter and tree height.  Collaborators at University of Tasmania and the CRC for Forestry are measuring the understorey, and modelling its contribution to site water use.  
Dr Sandra Roberts, Dr Rebecca Barton-Johnson, Dr Crispen Marunda
(a pdf of this article is provided for download below)