Sapling and coppice biomass heritabilities and potential gains from Eucalyptus polybractea progeny trials

Eucalyptus polybractea has been planted as a short-rotation coppice crop for bioenergy in Western Australia. Historical breeding selections were based on sapling biomass and despite a long history as a coppice crop, the genetic parameters of coppicing are unknown. Here, we assessed sapling biomass at ages 3 and 6 from three progeny trials across southern Australia. After the second sapling assessment, all trees were harvested. Coppice biomass was assessed 3.5 years later. Mortality following harvest was between 1 and 2%. Additive genetic variance for the 6-sapling estimate at one site was not significant. Sapling heritabilities were between 0.06 and 0.36 at 3 years, and 0.18 and 0.20 at 6 years. The heritability for the coppice biomass was between 0.07 and 0.17. Within-site genetic and phenotypic correlations were strong between all biomass assessments. Cross-site correlations were not different from unity. Selections based on net breeding values revealed positive gains in sapling and coppice biomass. Lower or negative gains were estimated if 3-year sapling selections were applied to the coppice assessments (−7.1% to 3.4%) with useful families culled. Positive gains were obtained if 6-year sapling selections were applied to the coppice assessment (6.4% to 9.3%) but these were lower than those obtained by applying coppice selections to the coppice assessment (8.4% to 14.8%). Removal of poor performing families and families that displayed fast sapling growth rates but under-performed as coppice will benefit potential coppice production. These results indicate that selections should be made using coppice data

An Analytical Framework for the Domestication of Mallee: the Agronomy, Genetics, Productivity and Economics of Biomass Production in a Dryland Agricultural System

This thesis addresses knowledge gaps in the productivity, breeding and economics of mallee eucalypts which have potential as a biofuel feedstock or for carbon sequestration. We assessed mallee productivity at 19 sites which ranged from 2.2 to 32.8 dry Mg/ha/year. Mallee planting configurations had significant effect on yield. Future breeding should include assessments of reproductive phenologies and selections for biomass should be made at coppice age. Mallee can be profitable under current Australian carbon prices

Flowering phenology in a Eucalyptus loxophleba seed orchard, heritability and genetic correlation with biomass production and cineole: breeding strategy implications

Reproductive synchronicity within a seed orchard facilitates gene exchange and reduces self-fertilisation. Here we assessed key flowering traits, biomass and foliar 1,8-cineole concentrations of Eucalyptus loxophleba (subsp. lissophloia and gratiae) in an open-pollinated seed orchard. Monthly flowering observations were made on 1142 trees from 60 families and nine provenances across 2 years. The percentage of trees flowering in both years was similar at 87%. There were differences between provenances and families within provenances for flowering traits, biomass and 1,8-cineole and interactions between provenances and year for flowering traits. Heritability of start and end flowering, and 1,8-cineole were high to moderate (h^2 = 0.75–0.45) and duration of flowering, propensity to flower and biomass estimates were moderate to low (h^2 = 0.31–0.10). Genetic and phenotypic correlations between flowering traits were high (rg = 0.96–0.63 and rp = 0.93–0.34) except between duration and end of flowering. The correlations were weaker between flowering traits and biomass or 1,8-cineole. ‘Dual flowering’, when trees underwent two reproductive cycles in a year, was responsible for out-of-phase flowering and those with low biomass and 1,8-cineole concentration should be removed from the breeding programme to hasten selection for desirable traits

Planting configuration affects productivity, tree form and survival of mallee eucalypt in farm forestry plantings

Mallee eucalypts have been extensively planted in the Western Australia wheatbelt for salinity mitigation and as a short-rotation coppice crop for the production of cineole and bioenergy feedstocks. Mallee has been planted in wide-spaced narrow belts (2–6 rows) within annual crops and pasture, but optimal planting configurations have not been determined. Here, we assess the biomass yield responses of Eucalyptus loxophleba ssp. lissophloia and E. polybractea to; four row treatments (1, 2, 4 and 6 row belts) and five within-row spacing treatments (1, 1.5, 2, 3 and 4 m). Thirteen years after planting, the row effects on plot-level biomass productivity of E. loxophleba ranged from 4.3 to 21.2 Mg ha−1 year−1. For E. polybractea, both row number and within-row spacing affected yield, which ranged from 2.7 to 18.8 Mg ha−1 year−1. For both species, the highest growth rates were observed in the one-row belts with shorter (< 3 m) within-row spacing. Within the belts, reductions of growth rate were observed with additional rows, due to increased competition and significant suppression of internal rows; and with wider within-row spacing, due to lower initial planting density. However, when including the area between belts, wider belts generated more biomass. For both species, average tree size decreased with additional rows and shorter within-row spacing. For both species, the number of stems per tree increased with wider within-row spacing, and also for E. polybractea, with fewer rows. The substantial variation in productivity, tree size and form found in these results will affect harvestability and ultimately the economic viability of future mallee plantings

A decadal multi-site study of the effects of frequency and season of harvest on biomass production from mallee eucalypts

© 2019 Elsevier B.V. Mallee eucalypts are hardy, woody perennials that are being developed as a short-rotation coppice crop in Australia for the production of eucalyptus oil, biofuels and other biomass products. The economic viability of this prospective crop is dependent on its ability to survive and regenerate following repeated harvesting of the above ground component. Here we report on survival and biomass yield of mallee belt plantings of Eucalyptus polybractea, E. loxophleba ssp lissophloia and E. kochii ssp plenissima, at 19 sites, under two harvest-frequencies (3–8 year cycles) and harvest seasons (autumn or spring) over a decade from 2006 to 2015. 16 sites had post-harvest mortality ranging from 1.0% to 12.2% while the remaining three sites with either shallow saline water tables or a silcrete hardpan failed. Average site dry biomass yield across treatments ranged from 2.2 to 32.8 Mg ha−1 yr−1. Higher yielding sites were generally characterised by pH between 3.8 and 8, ECe below 15.0 dS m−1 and high soil fertility. Lower yielding sites were generally near saline valley floors. After 7-years, biomass yield from unharvested treatments exceeded the average cumulative yield of harvest treatments at eight of the 16 sites, including all three E. kochii sites. For E. loxophleba, significant interactions were found between season and frequency of harvest with highest yields in long rotation spring treatments. There were also interactions between site and frequency of harvest, which were mainly driven by the variable performance of the uncut treatment. On average E. loxophleba yielded more biomass following spring harvests whereas E. kochii yielded more following autumn harvests. E. polybractea yield was unaffected by season or frequency of harvest; however, harvest treatments yielded more biomass than uncut treatments. After 10 years, at eight of the nine sites subjected to three 3-year cycles, no decline in biomass yield was observed. The site that declined in production was attributed to depletion of a sandplain aquifer by extensive mallee plantings. Overall, the results from this decadal study indicate that in warm-temperate semi-arid areas, such as the south-west of WA, mallees biomass can be harvested sustainably at most sites even in short (3-year) rotation cycles

Determinants of the economic viability of mallee eucalypts as a short rotation coppice crop integrated into farming systems of Western Australia

© 2020 The Authors. GCB Bioenergy Published by John Wiley & Sons Ltd Mallee eucalypts are being developed as a short rotation coppice crop for integration into agricultural systems in the south‐west of Western Australia. These have potential for biomass production for bioenergy, eucalyptus oil and generating carbon credits and to help control the extensive occurrence of dryland salinity. Some 12,000 ha of mallee planting has been undertaken since 1994, mostly in the form of wide‐spaced, narrow belts within the annual agricultural system. Production and market data were used to estimate levelized costs (LC) of mallee biomass production under different harvest regimes across 11 sites from 2006 to 2012. We found LC ranged from AUD40 to AUD257 fresh Mg−1. LC was most strongly determined by mallee production, followed by the crop/pasture rotation decisions of the landholder. Mallee harvest regime had minor impact on LC. Crop and pasture yield loss due to competition from the mallee belts accounted for 38% of costs, harvesting biomass was 32%, opportunity cost of the land occupied by the mallee belts was 16% while establishment and maintenance costs accounted for 14% of the costs. When income from carbon sequestered in mallee root biomass was included, the LC dropped by an average of 11% at the current Australian price of AUD15 Mg−1 CO2 equivalent (CO2e). The income from carbon sequestered in root biomass alone is unlikely to make mallee agroforestry economically viable. Hence, income from harvested biomass in the form of feedstocks for industry or carbon credits is necessary to make mallee agroforestry commercially attractive. LC for unharvested mallee belts ranged from AUD33 to AUD237 Mg−1. Where above‐ and below‐ground biomass is converted to CO2e at AUD15 Mg−1, the LC drops to AUD11–AUD64, with three of 11 sites likely to be profitable. These three sites were characterized by high biomass production with low agricultural gross margins