Assessing the utility of ALOS PALSAR and SPOT 4 to predict timber volumes in even-aged Eucalyptus plantations located in Zululand, South Africa

Abstract

In commercial forestry, regular terrestrial enumerations of the growing stock are required for the valuation, sustainable management and planning of current and future timber supplies. In this study we examined whether the combination of synthetic aperture radar (ALOS PALSAR) and optical satellite (SPOT 4) image data can accurately predict the timber volume of even-aged Eucalyptus plantations located in South Africa. Results from this study show that the combination of ALOS PALSAR and SPOT 4 produces a R² value of 0.68 for the planted model, whereas the coppiced model produced a R² value of 0.55. However, by including stand age as an independent variable in the stepwise model, there was a 15% improvement for the planted model, whereas the coppiced model produced a 27% improvement. The final model developed in this study produced a R² value of 0.83 and a RMSE of 31.71 m3 ha⁻¹ for planted stands, whereas the model for coppiced stands produced a R² value of 0.82 and a RMSE of 27.70 m3 ha⁻¹. As it is not practical or financially feasible for commercial forestry companies to carry out terrestrial enumerations for all plantations on an annual basis, the model developed in this study presents an alternative and accurate method to calculate timber volume for even-aged Eucalyptus plantations.

Keywords: commercial forestry, Eucalyptus species, optical remote sensing, saturation, synthetic aperture radar, timber volume