Forestry, bioenergy and climate – a way forward in Australia

Abstract

Sustainable forest management ensures that biomass removals do not exceed forest growth, maintaining stable carbon stocks. When biomass created as a byproduct of tree-harvesting for sawlogs or pulp is used for bioenergy generation, the carbon emitted in this process is re-absorbed by growing trees as part of the natural carbon cycling in sustainably managed forests. Thus, the use of biomass for bioenergy generation can make an important contribution to climate change mitigation as the world transitions away from fossil fuels. Bioenergy can broadly be classified into three key end-use categories: electricity, heat and transport fuels. In Australia, many small electricity-generation units are fuelled by biomass, and a number of larger grid-scale facilities are accredited to generate renewable energy credits under the Large Scale Renewable Energy Target (RET) scheme. The majority of these facilities use sugarcane bagasse as feedstock. A small amount of biomass is also cofired with coal (e.g. at the Vales Point power station in New South Wales – NSW). Some domestic facilities (e.g. Altus Renewables in Queensland) produce pellets from sawmill residues, with the pellets exported for use in power stations overseas. There is significant use of wood for domestic heating and also for industrial applications—in sawmills, for example, residues are used in boilers to generate heat for drying timber. It is likely that interest in the use of biomass for heat in industrial applications to displace fossil fuels would increase if current renewable energy incentives such as the RET also included allowances for heat generation; currently, however, the RET only covers electricity generation. There has been some interest in liquid transport fuel applications from woody material (e.g. jet fuel) but little tangible progress—although Boral in NSW recently investigated the potential for the production of renewable diesel from hardwood sawmill residues. Despite its potential, the development of a thriving bioenergy industry in Australia supported by biomass from sustainable forestry operations has not yet eventuated. There has been much promise, but numerous projects have ultimately failed. A number of recognised factors are linked to this chequered history, including issues with the regulatory environment, a lack of consistent policy signals, issues of social licence, misconceptions about the climate benefits of bioenergy, and poor access to information on available technology options. It is important to distinguish the various potential sources of forestry-derived biomass, which include residues from the harvesting of trees for higher-value products; biomass from dedicated energy crops; and residues from wood-processing facilities and end-of-life materials (e.g. construction and demolition – C&D – waste). The issue of sustainability is often raised when considering the use of forest harvest residues for bioenergy, including around the debate on climate benefits. Nevertheless, it is commonly accepted that forest bioenergy can deliver meaningful climate benefits if it displaces the use of fossil fuels and if the biomass is sourced from residues from sustainable forest operations or from energy crops established on marginal, unproductive land (e.g. Reid et al. 2019). Other concerns around the use of biomass for energy include the impact of residue removals on the future nutritional needs of the forest and the impacts on biodiversity caused by habitat removal. For native forests, a recent study in NSW demonstrated that it is possible to remove substantial quantities of harvest residues with minimal impact on future nutritional needs or habitat (Ximenes, Coburn et al. 2017). In plantations, the removal of residues for bioenergy may mean that fertiliser must be added in later rotations—this becomes a management decision. In Scandinavian countries, the high-nutrient ash obtained from the combustion of biomass is returned to the forest—in Sweden, around 50 000 tonnes of clean wood ash is spread each year in forests in the southern provinces (IRENA 2019). Large volumes of residues are generated during forest harvesting and also at wood-processing facilities. The ‘Australian Biomass for Bioenergy Assessment’ project has quantified and mapped organic residues from many sources, including sustainable forestry operations – at least 2 million tonnes of residues per year are generated during the harvesting and processing of wood in NSW alone. Although the bulk of forestry residues is derived from harvesting operations, localised opportunities exist associated with processing residues from sawmills and also from end-of-life timber products (e.g. C&D waste), which would otherwise be placed in landfills. This resource is currently underused and potentially available for bioenergy projects. Thus, there is a clear, underdeveloped opportunity that links sustainably derived forestry biomass, energy generation and climate change mitigation goals. Bioenergy can be considered the ‘forgotten renewable’ in Australia when its potential is compared to actual project development, especially in relation to other renewables such as solar and wind. Bioenergy has an advantage over intermittent renewables such as solar and wind in its ability to provide much-needed dispatchable energy, and it also has an important role to play in stabilising supply to the electricity grid, especially as the