Open Cut » Environment
A series of plantation forest trials were established in the late 1990s and early 2000s in the Upper Hunter coalfields to investigate the potential commercial viability of growing plantation forests as an alternative post-mining industry - either for wood products or carbon offsets. Following on from an earlier establishment trial (C10043), the focus of this research project was the ongoing management of the dryland plantations, which are now approximately 15 years old, with the objective of quantifying the benefits of an early non-commercial thinning and pruning regime.
Of the species trialled in this project, the best all round performer is Corymbia maculata (Spotted gum). While it has grown well on Buffer sites, an interesting finding has been that most stands of C. maculata have performed as well or better on the reshaped Overburden. While in general, thinning has not yet led to an increase in overall stand volume, at the majority of sites it has resulted in an increase in the mean dominant Diameter at Breast Height (DBH) and mean dominant Height (H) of trees. Visual assessments indicate that thinning is likely to result in stands of better form, potentially resulting in the growth of higher value timber products. Further measurements over the life of the plantations to final harvest age (35-40 years) are recommended before definitive conclusions can be drawn about the longer-term benefits of thinning and pruning.
The trial plots of Eucalyptus camaldulensis x grandis hybrids have to date yielded mixed results with the majority of Buffer plantings not performing as well as the C. maculata. Due to these highly variable results and in the absence of long-term data from these or other sites, use of this species as a commercial option cannot be recommended at this time. Other trialled species are also not recommended for future use for various reasons. The E. camaldulensis stands grew poorly and this is attributed to possible poor genetic stock. The E. camaldulensis x globulus planted at one site grew well initially but suffered from severe herbivorous insect attack between 2014 and 2016. The other species E. argophloia, E. molluccana and E. sideroxylon, while exhibiting very good early growth, have been outperformed by the C. maculata stands over the longer term.
An economic model is used to compare Forestry and Agroforestry with Grazing. Grazing (agistment of beef cattle) is the default land use on rehabilitated mined land and mining buffer land in the Upper Hunter. We evaluate Forestry (hardwood plantations) and Agroforestry (wide spaced hardwood plantation trees and pasture) as alternative land use options to Grazing. Expected returns from Forestry/Agroforestry are generated for Spotted Gum (C. maculata) using modelled growth and yield projections. Net present values and internal rates of return are generated for three scenarios: 'Base Case', 'Best Case' and 'Worst Case'. We find that Forestry and Agroforestry deliver comparable commercial returns (from carbon and wood products) to Grazing but with a different investment and risk profile.