Sustainability of forest bioenergy: Integrating bioenergy into forest value chains
Words by Mirjam Roeder, University of Manchester
The UK consumes about 25% of all globally produced forest-based wood pellets mainly to produce electricity in large-scale power stations that typically contribute 4% to the UK’s electricity supply. This makes the UK the largest consumer of wood pellets worldwide. Over 90% of these wood pellets are imported making the UK the largest global importer – reflecting over 40% of all wood pellets traded globally. Most of these wood pellets are sourced from North America where pellet production makes up less than 1% of the forest products by weight (Abiom 2016). These wood pellets are produced from forest residues (tree tops, branches, bark and low quality trees) and sawmill residues (sawdust and off-cuts). Available forest residues are predominantly not used for bioenergy, but are either left on the forest floor to decay or are burned at forest landing sites or sawmills.
As with all renewable energy technologies, for bioenergy to be a viable it needs to deliver energy with lower emissions compared to that generated from fossil fuels. The evaluation of associated emissions, climate change impacts and carbon balances of forest bioenergy has been done for various supply chains. Such assessments capture a snapshot of the emissions of the specific supply chain and carbon balance of a forest stand but are also subject to many uncertainties. If practices and processes change along the supply chain this has to be considered and possibly re-evaluated.
The other challenge is that there are many uncertainties, related to the different inputs, materials and technologies applied and varying practices at each stage within the supply chain (e.g. how wood is produced, how the forests are managed, how wood is processed and feedstock produced, and what energy conversion technology are applied). Each of these variations can be fairly easy assessed, reduced and controlled to improve the overall performance of the process. It becomes much more complicated to assess and assume impacts and related uncertainties considering natural variations within the system (e.g., how a forest grows, how seasons vary from year to year); social, economic and institutional conditions; and dynamics (e.g. how living conditions, perceptions, markets or policy develops); also how the potentially limited knowledge and/ or understanding of natural and behavioural processes.
Still, the common assessments analysing supply chain emissions and carbon balance can provide us with sufficient information to the evaluate systems and indicate possible outcomes and trends. Even regarding the uncertainties, which are less predictable we can get a comprehensive understanding of the scale of the range of potential impacts. Looking at forest bioenergy supply chains, we have a good knowledge and understanding of what is “good”, what is “bad” as well as what are the shades in between. Evaluating lifecycle emissions and carbon balances of such supply chains, even taking account of uncertainties, helps us to understand how we can reduce emissions to meet our emission targets. It also helps us to improve practices along the supply chain to maximise benefits, emission reductions and carbon savings. Whilst also helping us to identify where our knowledge is limited and where we need to do more research to understand these things.
Although simply assessing emissions and carbon balances is not sufficient on its own. We also need to understand what the forest bioenergy system is compared to, as this determines the context and trade-off of such systems. So we need to ask the questions of what we want to achieve by introducing bioenergy into the current system – is it simply to generate low carbon energy, or is it to specifically replace another fuel, to create an income for stakeholders, to create jobs, to support environmental benefits, to improve energy security, or to support a specific population group or industry. We therefore have to understand how forestry products are currently used, what are the dynamics of the current system, what are the impacts or benefits, who currently uses the products, what is replaced or substituted, how does it affect other product supply chains, who makes the decisions about access and utilisation - who benefits?
Especially when looking at forest bioenergy this picture becomes very complex. Sourcing bioenergy feedstocks from forests is just a small piece of a big mosaic. Forests are diverse and provide many different products and services for many different markets and end uses - bioenergy currently playing only a minor role in terms of revenue and amount of material. Nevertheless, forest value chains offer the integration of conventional forest products like sawn-timber, pulp and panel and bioenergy through the utilisation of forest residues such as tops, branches and bark of trees or trees and fibre of marginal quality, like trees affected by fires, pests and disease.
There are various sustainability measures in place setting standards for forest management. In addition many European nations such as the UK have regulatory and incentive schemes that aim to ensure that only biomass compliant with specific standards are eligible for subsidies. This is to ensure that bioenergy delivers significant emission reductions compared to fossil fuel derived energy and at the same time is not sourced in a non-sustainable manner.
Forest-based bioenergy can offer a great potential by both providing renewable low carbon energy as well as sequestering atmospheric carbon. This could be supported by the proposed Renewable Energy Directive of the EU, which aims to include that biomass is only sourced from countries that have ratified the Paris Agreement and are reporting their emissions and sequestration from forestry and land-use. This means that these measures are stricter than certification scheme for non-energy wood uses (e.g. sawn-timber, pulp, panel), which are currently not linked to emissions and carbon balances from wood product use.
Nevertheless, such sustainability and emission standards only capture a specific supply chain and cannot provide a guarantee that these criteria are met on a level beyond this specific supply chain and forest stand. To understand the full picture of forest management, supply chain emissions and carbon balance we need to consider the forest landscape, which is the sum of the different forest stands in a forest. In other words, sustainability schemes cannot necessarily capture how a specific forest stand is managed outside a specific time scale (e.g. outside one rotation from forest establishment to harvest) in the long-term (repeating rotations) and across all stands part of the forest landscape and how the rest of the forest is managed. Moreover, the way the forest stand is managed for this one rotation can then have an impact on how the forest stand grows in the following rotation.
It is important that such standards consider both ends and all involved actors of the supply chain – the supplier and consumer as well as related sectors and stakeholders along the supply chain. E.g., while the UK and EU incentivise forest bioenergy systems according to a specific emission threshold, the forest producers and managers in the producer nations are not necessarily driven by that but follow their standards of producing wood in a sustainable manner to be eligible for the main product markets, which usually is a wood product. This again shows that forest bioenergy cannot be seen outside the context of the forest sector. If policy makers and industrial sectors want to achieve high sustainability standards they need to consider and understand the different drivers and trade-offs for the various actors along the forest value chains. These might be very different depending on type of forest, management methods, main product markets and target groups for the forest products, hence we need to look beyond carbon and climate change impact, too.
Simply placing bioenergy into the energy sector will fail to ensure sustainable forest management and potentially forest carbon management. To ensure that bioenergy provides the required emission reductions and forestry maximises carbon benefits we need holistic and long-term approach to understand fully the impacts of forest management with integrated forest bioenergy; and not just forest bioenergy on its own. For this, assessments as well as sustainability standards and incentives need to consider why forests are grown, what for are the grown and who are the direct and indirect stakeholders and their trade-off of such value chains. Moreover, we need to consider what the drivers and benefits are for forest owners and managers and why they integrate or do not integrate bioenergy into their system. Hence, to understand the impacts of forest bioenergy we need context specific assessments, as environmental, climatic, economic, political and social conditions are various.
There is a robust scientific knowledge of the benefits and impacts of forest bioenergy and various research has shown that forest bioenergy can provide significant emission reductions and carbon stock benefits. Nevertheless, these are often subject to high uncertainties. Forest grow over many decades and therefore time of carbon sequestration and emission release from supply chain related activities and carbon release form burning forest biomass happen at a very different point in time. For this, we need long-term data to build reliable models to evaluate the impact of forest bioenergy integration and potential changes in management practices and with this on forest production and carbon stocks.
To ensure sustainability of and maximise carbon benefits from forest supply chains, context specific and transparent assessments based on real life date are required to make decisions on which value chains should be supported and which should not. This will help us to identify biomass sourcing and supply chain practices likely to have minimum impacts in line with climate change targets and sustainability standards.