Across-rotation factors affecting genetic improvement of Eucalyptus globulus in Australia
Creators: name: Whittock, SP
Publisher: name: University Of Tasmania
Year: 2023

description: In forest tree improvement, ensuring that a breeding objective (BO) is well defined yet broad enough to cope with changes over time, is problematic. Two of the major changes to occur in the Eucalyptus globulus pulpwood plantation industry that may impact on tree improvement that were investigated in this study are coppice management of 2nd rotation crops and international demands for improved sustainability (e.g. the trade in environmental services such as carbon sequestration). Coppice can provide a cheap alternative to replanting in the 2nd rotation. Regeneration following felling of a 9 year old progeny trial revealed significant genetic diversity in coppicing traits both within and between subraces. After 14 months, 67% of trees coppiced but subrace means varied from 43 to 73%. Heritabilities for coppice success (0.07) and subsequent growth (0.16-0.17) were low but statistically significant. The ability of a tree to coppice was genetically correlated with tree size prior to felling (r\\(_g\\) = 0.61), and with nursery-grown seedling traits such as the number of nodes with lignotubers (r\\(_g\\) = 0.66) and seedling stem diameter at the cotyledonary node (r\\(_g\\) = 0.91). These seedling traits were poorly correlated with later age growth and with each other. The results suggest coppicing is influenced by three independent factors - lignotuber development, enlargement of the seedling stem at the cotyledonary node and vigorous growth. A discounted cash-flow model was developed to compare the profitability of coppice and seedling crops in 2nd rotation E. globulus pulpwood plantations. A gain of 20% in dry matter production over the original seedling crop from 2nd rotation seedlings (through genetic improvement and provenance selection) would result in equivalent net present value (NPV) for 2nct rotation seedling and coppice crops. Incremental NPV was strongly affected by the level of genetic gain available (the genetic quality of 1 st rotation stock relative to the available genetically improved stock), and the productivity of coppice relative to the first rotation crop. The integration of environmental services (in the form of carbon seuquestration) into production system models to define economic BOs for the genetic improvement of pulpwood plantations was investigated. Carbon dioxide equivalent accumulation in biomass in the Australian E. globulus plantation estate between 2004 and 2012 was estimated at ~ 146 t CO\\(_2\\)e ha\\(^{-1}\\), of which 62 t C0\\(_2\\)e ha\\(^{-1}\\) were tradable in 2012 and a further 30 t C0\\(_2\\)e ha\\(^{-1}\\) were tradable in 2016. Where revenues for carbon sequestration were dependant upon biomass in a plantation, it was possible to determine whether economic BOs were sensitive to the revenue from carbon sequestration. The correlated response of BOs with and without carbon revenues (˜ívÆ\\({cG}\\)\\(_{H1}\\)) was 0.93. Where economic BOs were based on maximizing NPV by increasing biomass production, the consideration of carbon provided no significant gain in NPV.