Estimating potential harvestable biomass for bioenergy from sustainably managed private native forests in Southeast Queensland, Australia

Abstract

Background: Australia's energy future is at the crossroads and the role of renewable sources is in focus. Biomass from sustainably managed forests provide a significant opportunity for electricity and heat generation and production of liquid fuels. Australia has extensive native forests of which a significant proportion are on private land. However, there is limited knowledge on the potential capacity of this resource to contribute to the expansion of a biomass for bioenergy industry. In addition, there are concerns on how to reconcile biomass harvesting with environmental protection. Methods: We used regional ecosystem vegetation mapping for Queensland to stratify harvestable forests within the 1.8 m hectares of private native forests present in the Southeast Queensland bioregion in 2014. We used a dataset of 52,620 individual tree measurements from 541 forest inventory plots collected over the last 10 years. Tree biomass was estimated using current biomass allometric equations for Australia. Biomass potentially available from selective sawlog harvesting and silvicultural treatment across the bioregion was calculated and mapped. Results: Current sawlog harvesting extracts 41.4% of the standing tree biomass and a biomass for bioenergy harvest would retain on average 36% of felled tree biomass on site for the protection of environmental and fauna habitat values. The estimated area extent of harvestable private native forests in the bioregion in 2013 was 888,000 ha and estimated available biomass for bioenergy in living trees was 13.6 million tonnes (t). The spotted gum (Corymbia citriodora subsp. variegata) forests were the most extensive, covering an area of 379,823 ha and with a biomass for bioenergy yield of 14.2 t•ha −1 (with approximately 11.2 t•ha −1 of the biomass harvested from silvicultural thinning and 3 t•ha −1 recovered from sawlog harvest residual). Conclusions: Silvicultural treatment of private native forests in the Southeast Queensland bioregion, has the capacity to supply a large quantity of biomass for bioenergy. The availability of a biomass for bioenergy market, and integration of sawlog harvesting and silvicultural treatment operations, could provide land owners with additional commercial incentive to improve the management of private native forests. This could potentially promote restoration of degraded forests, ecological sustainability and continued provision of wood products.

A Review on the Potential of Forest Biomass for Bioenergy in Australia

“…In eighteen of these studies, the theoretical biomass potential is combined with the assessment of either available, technological, economical or environmental biomass potentials. Various studies have used allometric equations to predict the theoretical biomass potential based on in-field measures of height and diameter allowing them to estimate the overall above-ground biomass ratios [54][55][56][57][58][59][60]. For the purpose of bioenergy, these studies are rather informative literature on the ratio of above-ground biomass in order to assess the theoretical biomass potential without including any losses or alternative uses of the biomass.…”

Implications of Selective Harvesting of Natural Forests for Forest Product Recovery and Forest Carbon Emissions: Cases from Tarai Nepal and Queensland Australia

“…Data for the study were gathered from the Tarai region of Nepal and the Southeast region of Queensland. The case study site in Nepal is rich in commercially high-value natural forests dominated by Sal (Shorea robusta) [31] whereas the Queensland site is rich in high-value native hardwood timber with a dominance of Spotted gum (Corymbia maculata) [32]. Specifically, the Nawalparasi district of Nepal and the Withcott area of Queensland were selected for study, considering the availability of ongoing forest harvesting blocks (Figure 1).…”

“…For this purpose, stem density is the key and a sensitive factor as this determines the tree biomass [45]. Therefore, the average density of a commercially matured tree of each species was cited in the earlier studies: Forest Resource Assessment of the Department of Forest Research and Survey (FRA/DFRS) [31], Sharma and Pukkala [35] in the case of Nepal and Maraseni [46] in Queensland. Since the harvested trees were mature (over 30 years of age), the density of Spotted gum in Queensland was taken as 802 kg per m 3 [40].…”

“…* Total biomass of harvested trees including below-ground biomass. In both cases, the above-ground biomass is calculated as the product of above ground stem volume and base density of harvested tree species and then adding crown biomass using the proportion suggested by earlier studies [31,35] for Nepal and [44] for Queensland. Below-ground biomass is estimated as 25% of the stem biomass considering 0.25 root shoot ratio [59] for Nepal whereas it is taken as 0.26 for the Spotted gum in Queensland [46].…”

“…The highest figure for damage to seedlings and saplings in these sites is associated with a higher level of regeneration in the harvested area. Nepal had an average of 21,649 seedlings and 1662 saplings per ha [31] whereas Queensland Spotted gum-dominated native forests hosted up to 2500 regenerating stems per ha [81]. The larger trees and minimum regeneration supported minimal damage to the undergrowth and neighbouring trees [53], whereas in Nepal, the reverse applied with higher regeneration and wider variance in harvested tree size (28-56 cm in DBH and 8-30 m in height).…”