The effect of tree spacing on evaporation from an agroforestry experiment

Components of the water balance were measured at three spacings of Eucalyptus grandis planted into a pasture dominated by Setaria sphacelata cv. Kazungula in an agroforestry system. The experiment was carried out in a sub-tropical climate near Brisbane, Australia, where mean annual rainfall is 1099 mm. Total water loss per unit area by evaporation increased, and drainage losses decreased with increasing planting density. At the closest spacing, subsoil water contents were depleted to wilting point down to the maximum depth of measurement (5.6m). Trees planted at the wider spacings, where inter-tree competition for water was less, were able to exploit a larger volume of soil water stored in surface layers, so that soil water depletion at depth was less.