Eucalypt plantations in south-western Australia

Hardwood plantation forestry is a new and expanding industry in south-western Australia where Eucalyptus globulus plantations are established on agricultural land. First-rotation growth rates are high, partly because of previous use of fertilisers and annual leguminous pasture species by farmers. A series of inter-rotation experiments has been established at two sites with contrasting soils to investigate options for plantation management that will maintain soil fertility and stand productivity in subsequent rotations. These experiments include alternatives for managing harvest residues, use of inter-row legumes and nutrient application rate trials. After harvest, about one-quarter of the N and half of the P and Ca in the trees was exported from the sites in logs. Most of the exported N and P was in the wood, whereas most Ca was in the bark. Where burning was used to remove harvest residues and prepare the site for planting, more than 500 kg ha(-1) of N was lost from the more fertile site. Retention of harvest residues tended to increase soil moisture, moderate diurnal temperature fluctuations and enhance the pool of potentially available N. Soil organic matter content declined in the first two years following harvest, largely due to a reduction in the labile pool of soil carbon. There are indications of a reversal in this trend in the third year after harvesting, probably due to inputs of plant residue from turnover of roots. Early growth rates of trees were enhanced by retention of harvest residues, but longer-term measurements are needed to confirm this trend.