Environmental impacts of structural and concrete formwork plywood in Japan

Addressing climate change requires reducing greenhouse gas (GHG) emissions across industries. Plywood, a wood-based material, has the potential to be a carbon–neutral product if sourced from sustainably managed forests. However, fossil fuel resources are used at various stages of production, leading to GHG emissions. This study evaluates the environmental impacts of plywood manufacturing in Japan, focusing on structural and concrete formwork plywood, using life cycle assessment (LCA). Data were collected from 18 plywood factories across Japan, covering 64% of structural plywood and 94% of concrete formwork plywood production in the country. Both mass and economic allocation methods were applied. The results showed that structural plywood had GHG emissions of 166 kg-CO2eq/m³ under mass allocation and 185 kg-CO2eq/m³ under economic allocation. For concrete formwork plywood, GHG emissions were 205 kg-CO2eq/m³ and 229 kg-CO2eq/m³, respectively. Key contributors to emissions include electricity consumption and adhesives, whereas coatings play a significant role in concrete formwork plywood production. All the surveyed factories used biomass boilers, primarily fueled by in-house wood residue. Factories with on-site biomass power generation had lower GHG emissions owing to their reduced reliance on purchased electricity. The analysis also highlighted that optimizing the paints used in concrete formwork plywood production could significantly reduce environmental impacts. Furthermore, while biogenic carbon absorption and emissions are much greater than fossil fuel-derived emissions, ensuring sustainable forestry practices is critical for maintaining carbon neutrality in plywood production. This study provides representative LCA data for Japan’s plywood industry and identifies key areas for emissions reduction. These findings highlight the importance of efficient energy use, alternative low-carbon adhesives and coatings, and roundwood sourcing to minimize the environmental impact of plywood production.

Reducing greenhouse gas (GHG) emissions associated with human activities is urgent for addressing climate change issues. Japan has set the goal of achieving net-zero GHG emissions by 2050. Because wood stores carbon from the atmosphere, it can be considered a carbon–neutral and renewable material if appropriate forest management is implemented. However, fossil resources are used in processes ranging from forest management to wood product manufacturing, which lead to the emission of GHGs derived from fossil fuels. Wood products are required to reduce greenhouse GHG emissions.

Plywood consists of three veneers cut using rotary lathes or slicers [1]. A core veneer is sandwiched between the face and back veneers in a three-layer plywood. Depending on the application, additional veneers called crossbands may be added. Unlike lumber, plywood can support loads over a wide surface and has relatively uniform strength in both the longitudinal and width directions.

Plywood can be classified into structural plywood, concrete formwork plywood, and other types. Structural plywood is used in the load-bearing parts of wooden structures, whereas plywood for concrete formworks is used as a mold during concrete casting. Other types include specially processed plywood with printed wood-grain patterns on the surface.

Studies conducted in Japan [2, 3], the United States [4], China [5, 6], and Indonesia [7] have reported GHG emissions from plywood manufacturing. Komata et al. [2] collected data from two plywood factories located in Hokkaido, Japan. They reported that the GHG emissions up to plywood production were 121.7 kg-CO₂ eq/m³. No environmental impacts were allocated to by-products.

In Komata et al. [3], the impact of log and lamina imports was evaluated using the process data [2]. In the case of importing logs from Russia, the total GHG emissions for plywood production were 184 kg-CO₂ eq/m³, with a significant portion attributed to international log transportation. In the case of manufacturing plywood in Canada and importing it to Japan, the GHG emissions up to plywood production were lower than those of domestically produced plywood in Japan. However, the impact of plywood transportation was significant, resulting in total emissions of 125 kg-CO₂ eq/m³.

Southern pine was the primary raw material for U.S. softwood plywood. Based on mass allocation, the GHG emissions from fossil fuels used until the plywood manufacturing stage were 280 kg-CO₂ eq/m³. However, detailed contributions, such as the impact of adhesives, have not yet been reported. The study investigated factories accounting for 34% of production in the southeastern region of the U.S.

A Chinese study [5] reported GHG emissions of 538 kg-CO₂ eq/m³ based on mass allocation. Veneer production accounted for 48% of the emissions, followed by melamine–urea–formaldehyde (MUF) adhesive production at 21%. However, the data were collected from a Chinese company, making their representativeness uncertain. Another Chinese study [6] reported GHG emissions of 1,880 kg-CO₂ eq/m³ for plywood manufacturing. The drying and composition processes contributed 33% and 34% of the emissions, respectively. However, because the unit process data have not been reported, details such as the contribution of electricity consumption within the factory remain unclear. This study relied on primary data collected from a single factory.

In Indonesia [7], GHG emissions from plywood manufacturing using Sengon trees were evaluated. Based on mass allocation, the total emissions were 622 kg-CO₂ eq/m³, with adhesives contributing 375 kg-CO₂ eq/m³, accounting for the majority. This study assessed data from three factories in Central Java, Indonesia.

As seen in these cases, multiple life cycle assessment (LCA) studies on plywood exist, but GHG emissions vary significantly by region due to differences in raw materials and manufacturing methods. Although some imported logs are used in Japan, domestic logs constitute most of the material, making applying the foreign evaluation results inappropriate. While LCA studies exist for Japanese wood products, such as sawn timber [8], insulation boards, hardboards, particle boards, medium-density fiberboard (MDF) [9], and cross-laminated timber (CLT) [10], there is no established unit inventory for plywood using a process-based approach. Moreover, previous plywood studies have not collected data from multiple factories to ensure regional representativeness. The studies in Japan [2, 3] also focused only on two factories in Hokkaido and did not evaluate the variability across the entire country.

Therefore, this study aims to analyze the environmental impacts of plywood manufacturing in Japan, establish nationally representative LCA data, and identify key points for reducing environmental impacts. While various environmental impact categories were assessed, a special emphasis was placed on climate change, a critical environmental issue in Japan. This study focuses on structural and concrete formwork plywood, which accounts for most domestic plywood production.

Goal and scope definition

The environmental impact of the plywood was evaluated using LCA, as defined in ISO 14040:2006 [11]. The LCA begins by defining the goal and scope, followed by inventory analysis, impact assessment, and interpretation. The functional unit was the manufacturing of 1 m³ of plywood. This study assessed the structural plywood and the concrete formwork plywood in compliance with the Japanese Agricultural Standard (JAS) [12]. Structural plywood refers to the non-decorative plywood used in critical structural parts of buildings, whereas concrete formwork plywood is used as a mold to shape concrete structures.

Although the processes may vary slightly among factories, the primary production processes and system boundaries for plywood are illustrated in Fig. 1. In a typical plywood factory, roundwood is debarked and processed into veneers using rotary lathes. Roundwood is sometimes steamed beforehand to improve the veneer cutting workability. The cut veneers were dried using a dryer. After drying, the adhesive was applied, followed by assembly, lamination, and pressing. Pressing consisted of an initial cold press at room temperature to temporarily fix the assembled veneers, followed by a hot press that applied heat to cure the adhesive. In the finishing stage, the structural plywood is planned to be completed. The concrete formwork plywood was then painted to improve its peelability after hardening.

Steam is used in roundwood steaming, veneer drying, and hot-pressing processes. It is supplied through biomass and/or fossil-fuel boilers. The steam generated by the boiler is primarily used for processes, but in some boilers, it is also used for power generation. Biomass boilers use fuel sources, such as bark from the debarking process, offcuts from veneer cutting, and shavings from the finishing process. Offcuts and shavings are sold externally. They can also be used as pulp and paper manufacturing materials if sold before the adhesive application.

The system boundary includes plywood factories and forestry activities related to roundwood production and transportation. It also includes manufacturing various auxiliary materials and chemicals used in factories. As discussed later, the potential impact of the end-of-life stage was also estimated.

Foreground data

The data collection period was set to 2021, a year relatively unaffected by market disruptions due to COVID-19. As some surveyed factories underwent facility upgrades during the study period, data were collected from the operational periods closest to normal operations. Data were collected monthly for 1 year from all the factories.

Eighteen factories of 17 companies across Japan were selected based on geographical balance. Data on the manufacturing inputs and outputs were obtained. Data were collected from seven factories for the concrete formwork plywood. Factories producing concrete formwork plywood without structural plywood were excluded from the study. The geographical distribution of the surveyed factories is shown in Fig. 2.

Many plywood factories in Japan are located in the Hokkaido and Tohoku regions, and eight factories were selected. Four factories were chosen from the Chubu region, with significant plywood production. Table 1 summarizes the production scales of the selected factories. The two factories produce over 200,000 m³ of plywood annually. Seven factories had an annual production of 100,000–200,000 m³. One relatively small factory producing less than 2500 m³ annually was also included to account for differences in production scale.

In 2021, JAS-certified structural plywood had a grading volume of 1,808,817 m³ [13], of which the surveyed factories produced 64%. JAS-certified concrete formwork plywood had a grading volume of 37,716 m³ [13], with 94% produced by the surveyed factories.

Data entry sheets were created and sent to each factory in advance. On-site visits were conducted to verify and collect data on the annual procurement of raw materials, such as roundwood, adhesives, auxiliary materials, cutting tools, and energy consumed, such as diesel. Information regarding transportation methods and distances was also collected. In addition to plywood production, data on the production volume and sales prices of co-products such as wood chips were collected.

All surveyed factories used biomass boilers. The fuel for these boilers mainly consists of bark and wood chips generated within the factory. However, many factories do not accurately measure their biomass consumption. Therefore, we estimated the thermal energy consumption of biomass fuel based on the collected data on steam usage and boiler thermal efficiency of each factory. The boiler thermal efficiency was surveyed in each factory, but when unknown, a default value of 70% was applied. The efficiency of power generation was surveyed individually. If electricity is sold under the feed-in tariff (FIT) system, the environmental value is considered sold, and the assessment should be conducted assuming the use of grid electricity instead of biomass-generated electricity. However, in the factories surveyed in this study, all the generated steam and electricity were consumed within the manufacturing process.

Because plywood factories also produce multiple products, the allocation of environmental impacts is needed. In principle, allocation should be avoided by separating processes [14]. When unavoidable, physical-criteria-based allocation is considered a high-priority approach [14]. Mass-based allocation is considered appropriate, because economic and social fluctuations less influence it [15]. However, there are significant price differences between plywood and wood chips, and an economic allocation was used [16]. North American structural and architectural wood products require allocation by economic value when the main products exceed the co-product value by more than 10% [17]. The European standard EN16485:2014 [18] follows a similar allocation rule. Nonetheless, economic allocation assigns more resources and energy inputs to higher value products, leading to inconsistencies in mass balance. Thus, allocation methods significantly affect LCA results for wood products [16, 17, 19, 20], and different academic studies have employed various approaches [21].

This study minimized allocation through process disaggregation whenever possible. When allocation was necessary, both mass and economic allocation cases were evaluated. For example, the power consumption in the debarking process was divided between the bark and plywood, whereas the adhesives were fully allocated to the plywood. By providing unit processes for both allocation methods, users can select an appropriate approach based on their analytical requirements. Some factories also manufactured non-JAS-certified plywood. Since the manufacturing process for non-JAS-certified plywood is often the same as that for JAS-certified plywood, both were regarded as the same in this study.

The parameters used to establish the unit processes for plywood manufacturing, such as the apparent density, moisture content, and unit price, were derived from the literature [8, 22], statistical reports [23], research reports [24, 25], standards [12], and factory performance data. The parameters are listed in Table 2.

Background data

The background data used in this study were obtained from the Japanese process-based LCA database, IDEA version 3.4 [26]. For assessing the impact to climate change, data compliant with ISO 21930 [27] was used to calculate GHG emissions from both fossil fuel sources and land use and land use change (LULUC) sources. For assessing other impact categories, the LIME2 datasheet [26] was used.

The round woods used for Japanese plywood include Japanese cedar (Cryptomeria japonica), Japanese cypress (Chamaecyparis obtusa), Japanese larch (Larix kaempferi), and Sakhalin fir (Abies sachalinensis). The unit processes for roundwood production were obtained from the literature source [28]. As some roundwood was imported from North America, the environmental impact of imported roundwood was estimated using North American data [29]. The GHG emissions of roundwood used for the calculation are summarized in Table 3

Some factories use small quantities of the purchased veneers. As no published LCA data exist for veneer production, sawmilling data [8] were used as a proxy.

IDEA version 3.4 [26] includes environmental impact data for international ship transportation. However, these data are based on 2001 estimates. Updated environmental impact data were derived from continuous fuel efficiency improvements and stricter sulfur regulations since 2020 under the International Convention for the Prevention of Pollution from Ships [30]. Japan’s international container-shipping companies have been integrated into Ocean Network Express Pte., Ltd. GHG emissions (Scope 1) from Ocean Network Express Pte. Ltd. [31] were used to back-calculate heavy oil consumption, and this study used 3.34 g-CO₂ eq/tkm for international ship transportation. Sulfur oxide emissions were estimated assuming a 0.5% sulfur content in the fuel.

Impact assessment method

The primary objective was to assess the impact on climate change. The 100-year index from the IPCC Sixth Assessment Report [32] was used to characterize climate change impacts. IDEA version 3.4 accounts for GHG emissions from land use and transformation over a 50-year timeframe and these impacts were incorporated into this assessment.

In LCA, various environmental aspects beyond climate change can also be assessed. However, the reliability of the data may sometimes be low. Therefore, for reference, other environmental impact categories were assessed as preliminary assessments. LIME2 [33] was used as the impact assessment method. The preliminary assessed environmental impact categories included ozone layer destruction, acidification, urban area air pollution, photochemical ozone, human toxicity—cancer effects, human toxicity—non-cancer effects, aquatic toxicity, biological toxicity, eutrophication, land-use—occupation, land-use—transformation, and abiotic resource depletion.

Plywood production process (gate-to-gate)

Data on energy consumption, water consumption, raw material usage, auxiliary material usage, and waste disposal per 1 m³ of production at the factory level were compiled for structural plywood and concrete formwork plywood. The energy and water consumptions are presented in Table 4, and the other process data are summarized in Table 5. The data represent the weighted average values based on the JAS certification volumes at each factory, including both mass and economic allocations. The process names were aligned with those in IDEA version 3.4.

In all cases, the highest energy consumption was attributed to wood combustion in the biomass boilers. However, the fuel used in these boilers consists primarily of bark and chips generated in factories. Electricity usage was the source of the second highest energy consumption. The economic allocation results in higher values, because plywood has a higher unit price than wood chips and sawdust.

Concrete formwork plywood requires additional coating after structural plywood manufacturing, leading to higher energy consumption than structural plywood. However, whereas the structural plywood values represent the weighted average of 18 factories, the concrete formwork plywood values are based on the weighted average of only seven factories. Consequently, not all parameters increased in value.

The raw materials and service inputs of the factories are summarized in Table 4. These services include outsourced waste disposal. Japanese cedar was used as the primary raw material, followed by Japanese larch. Using imported round wood accounted for less than 8% of the total. The purchase volumes of externally sourced veneers for structural and concrete framework plywood were approximately 8.00 ×ばつ 10^–2 m³/m³ and 1.91 ×ばつ 10^–2 m³/m³, respectively. Concrete formwork plywood requires more paint than structural plywood.

In the factories surveyed in this study, roundwood was primarily imported from Canada, with some imports also coming from the United States. In addition, some factories imported Lauan logs from Malaysia; however, their share of the total imported roundwood volume was less than 0.1%.

Table 6 summarizes the transportation volume data per 1 m³ of plywood production. This data includes the transportation of roundwood, veneers, waste, and other materials and represents the weighted average of the surveyed factories. In terms of transportation volume (tkm), more than 95% of the total transport for both structural plywood and concrete formwork plywood was attributed to roundwood and veneers. Specifically, for structural plywood, over 90% of the transportation volume was associated with roundwood transport, while for concrete framework plywood, roundwood accounted for more than 77%. In the case of concrete formwork plywood, veneer transport accounted for 18%.

Regarding transportation modes, international maritime shipping constituted 77% of the total transport volume. The transportation volumes of auxiliary materials and waste were relatively small.

Under Japan’s Pollutant Release and Transfer Registers Law, companies emitting a certain amount of Volatile Organic Compounds (VOCs) must report their emissions to the government annually. In reality, small amounts of formaldehyde and other VOCs were emitted; however, none of the factories had sufficiently high VOC emissions to fall under the reporting threshold of the PRTR law. Therefore, VOC emissions were not included in the inventory data.

Plywood production (cradle-to-gate)

The GHG emissions from resource extraction to plywood manufacturing (cradle-to-gate) are summarized in Fig. 3, and results of other impact categories are summarized in Tables S1–S4 in the electric supplementary material.

Structural plywood

For structural plywood, the GHG emissions were 166 kg-CO₂ eq/m³ based on mass allocation and 185 kg-CO₂ eq/m³ based on economic allocation. Without considering production volume variations among factories, the standard deviation was 27.2 kg-CO₂ eq/m³ for mass allocation and 33.9 kg-CO₂ eq/m³ for economic allocation.

The impact of climate change was mainly attributed to adhesive (27%) and electricity consumption (22%). Roundwood contributed 17%, transportation 11%, and additives 16%. The influence of the purchased veneers, other energy sources, and paints was minimal. The destruction of the ozone layer also showed a composition similar to climate change, while the impact on transportation was small. Other energy sources primarily drive acidification and urban air pollution. Adhesives account for approximately 40% of hazardous chemical emissions. Additives significantly affect ecotoxicity and eutrophication. Roundwood production had a dominant impact on land use and occupation, whereas additives had a substantial effect on land-use transformation. Resource consumption was predominantly influenced by adhesives (83%).

Concrete framework plywood

For the concrete formwork plywood, the GHG emissions were 205 kg-CO₂ eq/m³ based on mass allocation and 229 kg-CO₂ eq/m³ based on economic allocation. Economic allocation resulted in higher values across all the impact categories. Without considering production volume variations, the standard deviation for concrete formwork plywood was 75.3 kg-CO₂ eq/m³ for mass allocation and 73.4 kg-CO₂ eq/m³ for economic allocation.

Adhesives contributed the highest share of GHG emissions at 22%, paints at 21%, electricity at 19%, and additives at 16%. The impact of ozone layer destruction followed a trend similar to that of the climate change assessment results. The "Other energy" contributed 49% to the acidification and 46% to the urban air pollution. Among the photochemical oxidants, adhesives and additives accounted for 26% and 24% of the total, respectively. Paints significantly affect hazardous chemical emissions, ecotoxicity, and resource consumption. Additives had the most substantial influence on eutrophication and land use transformation. For land use transformation, roundwood had a dominant contribution of 69%.

GHG emissions from roundwood production

The details of the GHG emissions from roundwood production are shown in Fig. 4. Although the GHG emission factor is lower compared to other domestically produced roundwood, the GHG emissions associated with Japanese cedar production were the highest in all cases. In structural plywood production, 41–43% of GHG emissions originate from Japanese cedar roundwood, whereas in concrete formwork plywood, this figure ranges from 50 to 54%. Following Japanese cedar production, larch production also contributed significantly to GHG emissions. Because the proportion of imported roundwood used was small, the GHG emissions associated with imported roundwood production were minimal.

GHG emissions from transportation

The GHG emissions associated with the transportation of roundwood, purchased materials, and waste are shown in Fig. 5. Domestic roundwood transportation has the greatest impact on GHG emissions because of the large proportion of domestically sourced roundwood. In structural plywood production, the impact of imported roundwood transportation accounted for 12% of mass and economic allocations. The GHG emissions associated with veneer transportation were relatively low.

Generally, concrete formwork plywood has a higher environmental impact than structural plywood because of the finishing process, which involves coating. Paints’ environmental impacts are particularly high regarding human health and ecotoxicity. It also contributes 17–19% to GHG emissions. Therefore, low-impact coatings are required to reduce the environmental impact of concrete formwork plywood production.

In structural plywood, 93% of the raw material was domestic roundwood, whereas in concrete formwork plywood, the figure was 95%, indicating that the share of imported roundwood was only a small percentage. Consequently, the GHG emissions from transportation were primarily influenced by domestic roundwood transportation. Considering the GHG emissions from imported roundwood, its contribution to manufacturing (Fig. 4) was minor, whereas its contribution to transportation (Fig. 5) was more significant. The associated GHG emissions are non-negligible, because imported roundwood is transported long distances. Although the current usage of imported roundwood is low, an increase in its use has amplified the impact of international transportation.

Roundwood production accounted for most of the impact regarding land use and occupation. However, this impact was calculated by summing the total land area used for production without considering the land types. Because forestland occupation has a relatively low environmental impact, it is not considered a critical environmental issue.

When the allocation method was changed from a mass-based to an economic-based approach, the environmental impacts increased in all cases. This is because plywood has a higher economic value than wood chips and other by-products, resulting in a larger share of the environmental impacts being allocated to it.

However, adhesives and paints were allocated entirely to plywood regardless of the allocation method. Since other inputs, such as roundwood and electricity, are subject to allocation, a mass-based approach results in a relatively higher proportion of the impact being attributed to adhesives and paints. When interpreting the LCA results of wood products, it is important to consider that the contribution of different factors may vary depending on the allocation method used.

Comparison among factories

For example, using the results based on mass allocation, three factories each with high and low GHG emissions were selected, and their simple averages are summarized in Fig. 6. In structural plywood production, the "High" factories showed more than double the impact of electricity consumption. While all factories used biomass boilers, some "Low" factories also had biomass power generation facilities, significantly reducing purchased electricity use. The "High" factories also had higher GHG emissions from adhesives and additives. Because there was little difference in roundwood-derived GHG emissions, it was inferred that the yield differences were minimal.

Significant differences were observed in the GHG emissions from the paints for concrete formwork plywood. The coating-related GHG emissions in "High" factories were approximately four times greater than in "Low" factories. While various types of paints were used, the GHG emission factors did not differ significantly, indicating that the differences were primarily due to the amount of coating applied. Although the standards for plywood include regulations on the performance of paint, there are no regulations regarding the thickness of the paint [12]. The difference in application amount may be related to the number of coating cycles and paint loss. By optimizing paint usage, "High" factories could significantly reduce the GHG emissions associated with concrete formwork plywood production. In addition, "High" factories consumed 71% more electricity. As with structural plywood, some "Low" factories included facilities that generated their electricity using biomass fuel.

In Japan, the supply of fuel wood chips has been strained due to the FIT system, making it difficult to introduce new biomass boilers. However, implementing biomass power generation remains an effective measure for reducing GHG emissions. Notably, the analysis results remained consistent even when evaluated using economic allocation.

Biogenic carbon and end-of-life

Because plywood is primarily made from wood, it retains biogenic carbon. The estimated dry densities of structural plywood and concrete formwork plywood, based on the roundwood composition shown in Table 5, are 347 kg/m³ and 332 kg/m³, respectively. The densities of each wood species were referenced from the literature [34]. Based on a carbon content ratio of 0.51 [34], the carbon content (CO2 equivalent) of structural plywood is calculated as 177 kg-C/m³ (649 kg-CO2 eq/m³) and that of concrete formwork plywood as 169 kg-C/m³ (620 kg-CO2 eq/m³).

This carbon is absorbed from the atmosphere as forests grow and released upon the disposal of plywood. In addition, the biomass fuel used in plywood factories releases carbon into the atmosphere during manufacturing. Therefore, the inflow and outflow of biogenic carbon, including at the disposal stage, were analyzed.

There are two approaches for assessing biogenic carbon impact in LCA, the 0/0 approach and the − 1/+ 1 approach [35]. In the 0/0 approach, a characterization factor of 0 is applied to the input flow associated with CO2 fixation from the atmosphere during biomass growth. Likewise, a characterization factor of 0 is used for CO2 emissions into the atmosphere from biomass combustion, ensuring a balanced input–output approach. On the other hand, the − 1/+ 1 approach assigns a characterization factor of − 1 for CO2 fixation from the atmosphere and + 1 for CO2 emissions into the atmosphere, maintaining consistency in the calculation.

In the previous sections, the assessment was conducted using the 0/0 approach. However, in this section, the – 1/+ 1 approach is applied to assess the flow of biogenic carbon. Plywood can be reused or crushed as a raw material for fibreboard production. In such cases, the biogenic carbon in plywood is not immediately released into the atmosphere. However, EN16485:2014 [18] evaluates this carbon as if released into the atmosphere.

This study also assumes that all biogenic carbon in plywood is released as CO2 during the end-of-life stage. In the previous sections, the impacts of LULUC were aggregated; however, in this section, they are separated.

In this study, the transportation distance of used plywood was not investigated; therefore, the plywood used was assumed to be transported 100 km by a 4-ton truck and crushed for energy recovery. The adhesives and paints used in the plywood were derived from crude oil. Assuming a carbon content of 50%, the fossil-derived CO2 emissions were estimated. The dismantling stage was not included in this analysis. GHG emissions during manufacturing were based on the results of mass allocation.

Regarding construction material, ISO21930:2017 [27] defines the material production stage as Module A and the disposal stage as Module C. In addition, "Extraction and upstream production" is categorized as Module A1, "Transport" as Module A2, and "Manufacturing" as Module A3. The disposal stage is further divided into "Transportation to waste processing or disposal" (Module C2) and "Waste processing" (Module C3). This study followed these classifications to organize the results.

The results of the structural and concrete formwork plywood analyses are shown in Fig. 7. It was estimated that 84 kg-CO2 eq/m³ from adhesives and an additional 19 kg-CO2 eq/m³ from paints in concrete formwork plywood would be released during disposal (C3). Compared to the GHG emissions from manufacturing (structural plywood: 166 kg-CO2 eq/m³, concrete formwork plywood: 194 kg-CO2 eq/m³), these emissions are not negligible, indicating that introducing lower-carbon adhesives and paints is crucial.

However, the removal and emission of biogenic carbon far outweigh fossil fuel-derived CO2 emissions. In "Extraction and upstream production" (A1), biogenic carbon used as biomass fuel and stored in plywood appeared to have significant negative values. The biogenic carbon balance was −1,244 kg-CO2 eq/m³ for structural plywood and −1,017 kg-CO2 eq/m³ for concrete formwork plywood. A portion of this carbon was released from biomass boilers during manufacturing (A3), while the biogenic carbon stored in the product (structural plywood: 649 kg-CO2 eq/m³, concrete formwork plywood: 620 kg-CO2 eq/m³) was released at the end-of-life stage (C3).

Because biogenic carbon is originally absorbed from the atmosphere, it was evaluated as a carbon–neutral emission. However, if forests are not regenerated, the products cannot benefit from carbon removal through "extraction and upstream production" (A1) [27]. While reducing fossil-fuel-derived GHG emissions is important, the most crucial factor is to ensure that raw materials are sourced from sustainably managed forests [36].

Comparison with other studies

Komata et al. [2] reported GHG emissions of 121.7 kg-CO2 eq/m³ up to the plywood manufacturing, based on data from factories in Hokkaido. Since their study allocated the total environmental impact entirely to plywood, this approach is more comparable to economic allocation, which generally assigns a higher proportion of emissions to plywood than mass allocation.

In this study, the GHG emissions of structural plywood were calculated as 185 kg-CO2 eq/m³ under economic allocation, approximately 1.5 times higher than the value reported by Komata et al. [2]. However, when examining unit process data, electricity consumption in Komata et al. [2] was 113 kWh/m³, whereas in this study, it was 84 kWh/m³. If the unit process data reported by Komata et al. were used with the background data from this study, the estimated GHG emissions would be 199 kg-CO2 eq/m³. The logs were evaluated as entirely domestic Japanese larch.

This suggests that while improvements have been made at the unit process level compared to the reported data [2], the increase in GHG emissions is likely due to changes in background data. Background data continuously undergo quality improvements. In addition, following the 2011 Great East Japan Earthquake, the shutdown of many nuclear power plants resulted in a higher electricity GHG emission factor compared to previous years. These factors are presumed to have contributed to the observed differences in results.

Data quality check and limitations

Annual data were collected from 18 factories in Japan. Consequently, the data set has high temporal, technological, and geographical representativeness. While IDEA version 3.4, Japan’s most comprehensive LCA database, was primarily used, higher quality data were applied to key processes, such as roundwood production and international container transport. The environmental impact of the purchased veneers was approximated using sawmill data. However, because its contribution to the results was minor, its effect on the overall findings was considered negligible.

"Other energy" significantly influenced the environmental impact categories of acidification and urban air pollution, primarily due to sulfur oxides (SOx) and nitrogen oxides (NOx) emitted from factory biomass boilers. The "waste wood combustion" process in IDEA version 3.4 was modeled based on data from general waste incineration without specifying the source. However, biomass generally has a low sulfur content, and Japan’s Air Pollution Control Act regulates emissions from factory biomass boilers. Therefore, there is a high likelihood that SOx and NOx emissions are overestimated. Future studies should incorporate more refined and accurate data.

As plywood is primarily made from wood, a carbon–neutral and renewable resource, its widespread use is expected to be a climate change mitigation measure. This study assessed the environmental impacts of structural and concrete formwork plywood from raw material production to manufacturing. Annual data were collected from 18 factories producing structural plywood and seven factories producing concrete formwork plywood, covering 64% and 94% of domestic production, respectively, making the data set highly representative.

The results showed that the GHG emissions of structural plywood were 166 kg-CO2 eq/m³ under mass allocation and 185 kg-CO₂ eq/m³ under economic allocation. For concrete formwork plywood, GHG emissions were 205 kg-CO2 eq/m³ under mass allocation and 229 kg-CO₂ eq/m³ under economic allocation. The primary contributors were electricity and adhesives, whereas for the concrete formwork plywood, the paints used for coating also significantly impacted GHG emissions. In terms of other impact categories, adhesives accounted for several tens of percent of the impact in resource consumption, photochemical oxidants, and human toxicity. Although there is some uncertainty in the data, further reduction of the environmental impacts of adhesives is desirable.

When comparing factories with high and low GHG emissions, those with higher emissions contributed more to the consumption of purchased electricity. Factories with lower GHG emissions included those generating biomass fuel power, significantly affecting the results. Although there are resource constraints on biomass fuel procurement, its introduction has resulted in clear GHG reduction. High-emission factories use more paint for concrete formwork plywood. This finding indicates that optimizing the coating application can reduce the environmental burden.

The amount of biogenic carbon involved in plywood manufacturing is much greater than that of fossil fuel-derived carbon. Therefore, ensuring that roundwood is sourced from well-managed sustainable forests is crucial for maintaining the carbon neutrality of plywood products.

The data sets used and/or analyzed in the current study are available from the corresponding author upon reasonable request, except for companies’ proprietary data and data licensed by third parties.

• (2025年10月02日 追記)

  02 October 2025

  The original online version of this article was revised: The correct values included in the article PDF

  (追記ここまで)

BDt:

Bone dry tonne

CLT:

Cross-laminated timber

FIT:

Feed-in Tariff

GHG:

Greenhouse gas

HHV:

Higher heating value

JAS:

Japanese agricultural standard

LCA:

Life cycle assessment

LULUC:

Land use and land use change

LHV:

Lower heating value

MAFF:

Ministry of Agriculture, Forestry and Fisheries

MDF:

Medium-density fiberboard

MUF:

Melamine–urea–formaldehyde

VOC:

Volatile organic compounds

The authors thank the 18 companies that provided the plywood production data for this study. The authors express their gratitude to the Japan Plywood Manufacturers’ Association for coordinating the survey.

This research was supported by grants from the Forestry Agency, Japan.

Authors and Affiliations

1. College of Policy Science, Ritsumeikan University, Iwakura-cho 2-150, Ibaraki, Osaka, 567-8570, Japan

   Katsuyuki Nakano

2. Tokyo University of Agriculture and Technology, Toyogaoka 2-11-2-103, Tama, Tokyo, 206-0031, Japan

   Nobuaki Hattori

3. Sustainable Management Promotion Organization (SuMPO), Uchikanda 1-14-8, Tokyo, 101-0047, Japan

   Masahiro Koide & Mai Imago

4. S-Pool Blue Dot Green, Sotokanda 3-12-8, Chiyoda, Tokyo, 101-0021, Japan

   Yuta Yamada

5. Usuki Energy, Sashiu 5154-1, Usuki, Oita, 875-0001, Japan

   Takuya Ogawa

6. Japan Wood Energy, Kizuna no Mori 2 F, 4-3-1 Higashi-Ome, Ome, Tokyo, 198-0042, Japan

   Yoshiki Toyoshima

Contributions

Conceptualization: Nobuaki Hattori; methodology and formal analysis: Katsuyuki Nakano; investigation: Masahiro Koide, Mai Imago, Yuta Yamada, Takuya Ogawa, and Yoshiki Toyoshima; writing—original draft preparation: Katsuyuki Nakano; writing—review and editing: Nobuaki Hattori; funding acquisition and supervision: Nobuaki Hattori.

Corresponding author

Correspondence to Nobuaki Hattori.

Consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

The original online version of this article was revised: The correct values included in the article PDF.

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

Reprints and permissions