Life cycle greenhouse gas emissions of woodchip-paved walkways using tsunami salt-damaged wood: examination in Otsuchi, Iwate Prefecture

Climate Change Mitigation Potential of Wood Use in Civil Engineering in Japan Based on Life-Cycle Assessment

“…Meanwhile, the lack of decay over long periods of log piles stored underground has been reported regarding the biodegradation in wood [44,45]. In contrast, the speed of the decay in the other applications is not scientifically clear [34][35][36][37]46]. Therefore, this study did not consider the decrease of carbon storage in wood as a result of the biodegradation in wood for the operational period.…”

“…where ACSW (t-CO 2 eq/year) is the year-to-year change in the amount of carbon stored in wood, CSW (t-CO 2 eq) is the carbon storage in wood in a given year, WS (m 3 ) is the volume of wood stock used in civil engineering, DW (t/m 3 ) is the density (oven dry mass over air dry volume) of wood (0.45 for coniferous wood) [43], CC (t-C/t) is carbon content of oven-dried wood (0.50) [43], CD (t-CO 2 /t-C) is conversion factor from the weight of carbon to the weight of carbon dioxide (=44/12), WU (m 3 /year) is the wood product use potential in civil engineering as described in Section 2.1, LT (-) is the lifetime function, n (years) is the number of years elapsed, r (-) is the rate of decrease (0.2), and a (years) is the civil engineering lifetime (half-life) (infinite for log piles and wooden check dams; 10 years for woodchip-paved walkways and wooden guardrails; 30 years for wooden noise barriers) [33][34][35][36][37]. Additionally, t represents the year, and i is an index denoting the respective wood applications (log pile, wooden check dam, woodchip-paved walkway, wooden guardrail, and wooden noise barrier).…”

“…The maximum potential assumes that woodchip-paved walkways will account for 10% of the Road Act coverage annual (i.e., 400 ha/year) and 100% of the annual forestry road coverage (i.e., 400 ha/year) Sustainability 2018, 10, 561 4 of 19 in the same year. We estimated the potential volume (m 3 /year) of wood use for woodchip-paved walkways by multiplying the annual paving area (ha/year) for such walkways by the usage volume of woodchips per unit paving area (0.06 m 3 /m 2 ) [35]. Values from 2018 to 2049 were interpolated using a sigmoid curve (Figure 1).…”

“…Many prior studies [3,7,16,27,[34][35][36][37] assumed the biogenic carbon (CO 2 ) balance of wood in the LCA and the CFs to be carbon-neutral. In other words, they had no effect on the CO 2 concentrations in the atmosphere; thus, the biogenic carbon balance was considered zero.…”

“…There are few prior research cases of LCA targeting wood use in civil engineering in Japan. Although studies have analyzed the life-cycle GHG emissions from wood use in civil engineering and the emission reductions resulting from substituting wood for non-wooden materials [33][34][35][36][37], these studies have targeted only individual applications, including log piles [33], wooden check dams [34], woodchip-paved walkways [35], wooden guardrails [36], and wooden noise barriers [37]. The future availability of wood for civil engineering structures in the country as a whole and the associated nationwide potential for climate change mitigation remain unclear.…”