Site index prediction of 'Eucalyptus dunnii' Maiden plantations with soil and site parameters in sub-tropical eastern Australia

The 'Eucalyptus dunnii' Maiden plantation estate in north-eastern NSW and south-eastern Queensland is significantly expanding on ex-grazing land. Thirty-one growth plots (average age 5.2 y) covering a latitudinal range of about 3.2° (370 km) and at altitudes from 8 m to 740 m asl in NSW were used to evaluate the correlation of site, soil and climatic variables with growth of 'E. dunnii'. Using height at an age of 10 y as a standard, site indices for 'E. dunnii' across the 31 sites averaged about 16 m, ranging from around 5 m to 26 m. The factors available-water storage capacity of the soil, rainfall and altitude accounted for 62% of the variation in site index. Inclusion of measures of fertility did not improve the predictive capacity of the model, possibly because of the limited size of the data set with soil chemical analyses. The predictive model, based on simple, easily assessable site factors, has the capacity to improve the quantitative evaluation of the productivity of sites for 'E. dunnii' plantations. The need for a simple field assessment procedure for selection of suitable sites was highlighted by the wide range of productivity exhibited across the plots.