INVESTIGATION OF THE FEASIBILITY OF USING TRUNK GROWTH INCREMENTS TO ESTIMATE WATER USE OF EUCALYPTUS GRANDIS AND PINUS PATULA PLANTATIONS
The water use of forest plantations remains a topical subject in light of recent changes to water law, as well as continuing debate over the hydrological impacts of various types of land use. While sap flow and micrometeorological techniques exist to allow direct measurement of forest water use, their usefulness in resolving land use disputes is currently limited for the following reasons:
An alternative approach to the estimation of plantation water use was suggested by the results of a previous investigation into the relation between annual trunk volume increments and cumulative annual water use of Eucalyptus grandis trees. The study was conducted in Kruisfontein Plantation (White River district, Mpumalanga), and involved a full year of growth and sap flow measurement in 17 trees growing on a wide range of site quality. A surprisingly tight, linear relation was found between annual volume growth increment and cumulative annual sap flow, suggesting that this measure of the efficiency of water use did not differ significantly among the trees. Further data from a Pinus patula experiment in the White River area (Witklip Plantation) revealed a similar efficiency of water use.