In the last two decades, cross-laminated timber – a wood product made from the crosswise layering and lamination of structural grade timber – has become an attractive alternative to concrete and steel, due to its potential for scalability, sustainability, strength, and flexibility, as well as its suitability for incorporation into fast, modular off-site construction techniques (Mallo and Espinoza 2014; Brandner et al. 2016). Because cross-laminated timber has a comparatively high strength-to-mass ratio, it can be used for walls, floors and ceilings in hybrid reinforced concrete or steel systems in low- to mid-rise buildings, one of the fastest growing markets in emerging economies (Schmidt and Griffin 2013). In many cases, governments are modifying laws and national codes that previously restricted the use of timber construction systems in tall buildings, to now promote the use of wood (Umeda 2010; Sinclair 2019).
Local and regional studies have found that substitution practices using mass timber could reduce global CO2 emissions 14-31 per cent and global fossil fuel use 12-19 per cent (Oliver et al. 2014; Pilli, Fiorese and Grassi 2015). More conservative estimates, however, show lower carbon storage potential and highlight the vulnerability of such models to market shocks (Johnston and Radeloff 2019). Mass timber buildings have demonstrated over 10 per cent lower operational energy compared to similar concrete buildings (Chen 2012). When accounting for 55 per cent recycling and 45 per cent energy recovery rates for end-of-life cross-laminated timber (John et al. 2009), mass timber buildings have shown 40 per cent emission savings and lower environmental impacts (John et al. 2009; Robertson, Lam and Cole 2012; Laguarda-Mallo et al. 2014).
As more country-specific studies (particularly in the developing world) examine the potential of timber building materials to store carbon and mitigate climate change, this can inform regional differences in the climate mitigation potential of wood products and develop incentives for sustainable forest management.
Figure 4.2 Global trends in harvested wood products,1960-2018
Use of industrial roundwoodfor wood-based panels and veneer sheets has increased significantly.
Timber has been used as a construction material and for diverse building products, such as structural beams, panelized boards, and walls and window framing. However, increased demand for such applications requires the establishment and implementation of safeguards that ensure responsible timber sourcing. In 2020, the global wood harvest came from two main sources: forest plantations (which accounted for 8 per cent of global cropland) and natural forest area (4 per cent of the global total) (Evans 2009; Mishra et al. 2022).
Currently, the overall rate of timber harvesting and deforestation in natural forests worldwide is faster than the overall regrowth of forests (Pendrill et al. 2019; Zhang et al. 2020). Timber demand is rising both in emerging economies, which use wood resources largely for fuel, and in developed countries, which use it mainly for building materials and paper products. Globally, the use of harvested industrial roundwood for products such as wood-based panels and veneer sheets increased significantly between 1960 and 2018 (see Figure 4.2).
Relative to major end-uses such as fuel and paper, the conversion of timber into wood building materials offers huge carbon reductions because these materials can serve as long-term carbon storage over a building’s lifetime (Churkina et al. 2020; Mishra et al. 2022). However, this model of building materials as a “carbon sink” assumes that sustainable replanting of trees occurs. Currently, this is the case only partially in Europe and North America, where the rising demand for wood products is coupled with a capacity for afforestation practices. In tropical and subtropical forests, increased logging drives dangerous levels of deforestation, ultimately reducing the long-term capacity of natural forests to sequester carbon (Vogtländer, van der Velden and van der Lugt 2014; van der Lugt et al. 2015).
In total, an estimated 38 per cent of the world’s wood products are used in the built environment, roughly 1,800 million tons in 2020 (FAO 2020). Around 10-30 per cent of the timber traded worldwide is harvested illegally, a share that may reach 90 per cent for tropical hard and soft woods (Grace Farms Foundation 2022). Illegal logging operations are valued at up to $100 billion, or an estimated 10-30 per cent of the global timber trade (Grace Farms Foundation 2022). Globally, as much as half of illegal logging is dependent on forced labour. In addition to the hazardous nature of logging activities, exploitative conditions may include threats, poor living and working conditions, excessive work hours, non-payment of wages and debt-based coercion (Vidican 2020). Gender inequalities are also rife, with women often engaged in uncompensated informal work (see Box 4.1).
Across the timber and biomass industries, gender norms and relations play a critical role in complex resource management and biodiversity conservation practices (Shiva 1992; Agarwal 2010; Kiptot and Franzel 2011). Global patterns of gender norms largely show that men participate in and manage seasonal forestry practices linked to cash income, whereas women have been responsible for the daily provision of forestry resources for food and broad household needs that lie outside of formally remunerated work (Shiva 1992; Agarwal 2010). In this sense, not only is the daily multi-tasking nature of women’s labour largely invisible, but the likelihood of expanding women’s participation in commercially productive roles is restricted due to the heavy workload.
Such norms are woven deeply into the social organisation of agricultural and industrial communities and have historically normalised the role of women and children as an informal community “support workforce” to service a primary male-dominated labour and management workforce (Arora-Jonsson 2014). This paradigm has led to policy gaps in valuing and supporting forestry extension services (Yokying and Lambrecht 2020; Nara, Lengoiboni and Zevenbergen 2021). Critically, when government policy focuses protection and job security solely on primary male forestry workers, this increases the dependence of the women-dominated workforce, particularly in terms of economic and land-use transition (Reed 2003).
Global studies have documented the role of women in the selection, propagation and marking of “wild” plant resources, effectively serving as biodiversity custodians (Shiva 1992; Howard 2003a; Howard 2003b; Kiptot and Franzel 2011). In China, women farmers have been the driving experts behind maize breeding (Shiva 1992; Song 1998; Song and Jiggins 2003). Studies in South Asia show the “snowball” impact of vertical mobility in female executive leadership positions, leading to increased female participation in timber resource co-management and decision-making (Agarwal 2010). In Sweden, while women represent 2 per cent of the construction sector workforce, a national study found that women accorded higher interest and importance to environmental issues but had lower influence on environmental outcomes (Wallhagen, Eriksson and Sörqvist 2018). Such patterns offer important foundations for destigmatizing and increasing women’s environmental participation and leadership across all levels in the buildings and construction labour sector.
Given that women face barriers to accessing credit and loans, financial institutions need to service and design loan collateral systems that are suitable to individuals and women collectives (Demirgüç-Kunt, Klapper and Singer 2013). While financial inclusion serves as a basis for bringing women to the table, governmental programmes and policies need to expand women’s access to new technologies, marketing information and training to sustain their participation on the ground (Kiptot and Franzel 2011; Coleman and Mwangi 2013; Agarwal 2015).
Figure 4.3 Embodied carbon balance of cross-laminated timber and forest by-products
Producing cross-laminated timber both stores and emits carbon, and the use of by-products from the process also offers opportunities for carbon storage.
Carbon emissions in the timber industry are concentrated in the phases of harvesting, transport and wood manufacturing (Steel, Officer and Ashley 2021). Previous estimates of CO2 emissions from timber harvesting underestimated emissions associated with pesticides, fertiliser and herbicide use as well as “clear-cuts” (the decaying logs and residues from logging). Together, these account for an estimated 15 per cent of logging emissions (Lippke et al. 2011; Hytönen and Moilanen 2014). In the United States of America, even when long-term carbon storage in wood products is taken into account, the CO2 emissions from timber logging and wood manufacturing exceed those from the residential and commercial sectors combined (Talberth 2019).
The manufacturing of structural beams, panels and engineered wood products relies heavily on the use of toxic, chemical glues and fossil fuel energy (Bergman et al. 2014). However, emerging timber-based materials such as cross-laminated timber and forestry by-products offer the potential to balance out these emissions over the building life cycle through carbon storage (Lan et al. 2020) (see Figure 4.3). As efforts to model the global storage of carbon in wood products advance, a key area for long-term CO2 emission reduction is through improving harvesting practices and wood manufacturing processes (Buchanan and Levine 1999; Talberth 2019). Important efforts to advance improved harvesting practices and to reduce pressures on tropical forests are occurring in West Africa (see Box 4.2).
Policies targeting the owners of industrial forestlands are key to improving sustainable management of natural forests and transitioning to productive plantations (Pirard, Dal Secco and Warman 2016).
Policies and plans should encourage afforestation of a diversity of softwood and hardwood tree species and reduction in the use of chemical herbicides and fertilisers.
Using biomass from clear-cuts as an on-site fuel source is a key near-term solution to avoid CO2 emissions and fossil-based electricity use (Gustavsson and Sathre 2011; Bergman et al. 2014).
For tropical forest production countries, adopting forest certification and timber tracking management practices could reduce emissions from deforestation and forest degradation by 29-50 per cent and improve carbon storage in sawn wood products and reduce wood waste by 14-184 per cent (Sasaki et al. 2016).
Clear-cuts and off-cuts from wood manufacturing have potential to serve as feedstocks for use in panelling, boards, furniture and flooring applications.
Recuperation of forest detritus and upgrading infrastructures could minimise tree felling for primary timber and save vast amounts of carbon by helping to reduce forest fires (Yale Carbon Containment Lab 2022).
Encourage upgrading of existing infrastructure to use renewable energy sources in wood manufacturing.
Replacing petrochemical glues with bio-based adhesives would reduce embodied emissions while improving the mechanical and hygrothermal performance of wood and reconstituted wood products.
Improve social acceptance and address regulatory barriers governing fire safety in buildings.
Key policy incentives aimed at stimulating market demand are needed to broadly promote the use of renewable, bio-based materials such as timber.