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• Substitution factors for forest products for the Canadian context were developed. • Substitution factors ranging from 0.51 to 0.91 tC/tC were found. • They will lead to more accurate assessments of the forest GHG mitigation potential. • These factors will help governments to manage forest and fight climate change. Evaluating the climate change mitigation potential of the forest sector requires a holistic approach based on forest carbon (C) sequestration, C storage in harvested wood products (HWP) and substitution on markets. High uncertainty is associated with substitution factors, that express avoided fossil greenhouse gas (GHG) emissions from the use of forest-based products in replacement of GHG-intensive materials and fossil fuels. Few studies have focused on the development of substitution factors in Canada, resulting in the use of unrepresentative generic data. Here, we provide a framework to reduce uncertainties related to substitution factors for primary wood products in a Canadian context. A life cycle assessment framework is used to quantify fossil GHG emissions for a baseline and a wood-intensive scenario. For solid product substitution, we focused on the construction sector and analyzed a range of innovative wood buildings with steel and reinforced concrete as alternative materials. We found non-weighted averages of 0.80 tC/tC for sawnwood and 0.81 tC/tC for panels. For energy substitution, we analyzed cases with different specifications on biomass product, facility type and alternative fossil fuel source in non-residential heat production and biofuel transportation sectors. We found a non-weighted average of 0.80 tC/tC for non-residential heat production and 0.51 tC/tC for biofuel transportation, that can be interpreted as 0.91 tC/tC for heavy fuel oil, 0.69 tC/tC for light fuel oil and 0.68 tC/tC for natural gas substitution. These results provide a benchmark for substitution factors in Canada, to help guide forest management strategies for climate change mitigation. [ABSTRACT FROM AUTHOR]

• Soil organic carbon (SOC) stabilities were studied in two agroforestry systems. • We studied hedgerow and shelterbelt systems and their component land-uses (cropland vs forest). • The biological stability of SOC was higher in hedgerow than in shelterbelt system. • The biological stability of SOC was higher in cropland than in forest land-use. • Agroforestry system by land-use interactively affected the thermal stability of SOC. Agroforestry systems play important roles in carbon (C) sequestration in western Canada. However, the effect of agroforestry system type and their component land-uses (forested area and cropland) on soil organic C (SOC) stability is poorly understood. We studied SOC stability in surface soils from two agroforestry systems (shelterbelt system and hedgerow system) and their component land-uses (forested area and cropland) in western Canada. A 61-day laboratory incubation was used to assess SOC biological stability, and compared to thermal stability measured during ramped combustion. The shelterbelt system had a lower biological stability than the hedgerow system as indicated by the higher cumulative soil respiration and SOC loss during incubation. Cumulative respiration and SOC loss during incubation in the forested area was 1.63 and 1.57 times that in the cropland, indicating a lower SOC biological stability in the former. Thermal stability indicators, CO 2 -T 50 (the temperature at which half of the CO 2 is produced), DSC-T 50 (the temperature at which half of the exothermic energy of the SOC is released) and ROI (return on energy investment) were influenced by the interactive effects of the agroforestry system by land-use, while TG-T 50 (the temperature at which half of the exothermic mass is lost) and Ed (energy density) were influenced by land-use and the interactive effects of agroforestry system by land-use. Hedgerow cropland had a higher SOC thermal stability (higher TG-T 50) than the hedgerow forested area, while there was no difference among shelterbelt cropland, and the forested areas of shelterbelt and hedgerow system. We conclude that planting trees on agricultural land to form agroforestry systems alters SOC biological and thermal stabilities, and the hedgerow system may have a more stable SOC than the shelterbelt system, thus, maintaining the hedgerow system may enhance C stability, promote C sequestration and climate change mitigation. [ABSTRACT FROM AUTHOR]

Improved land stewardship is necessary for climate change mitigation. As such, actions are needed to increase carbon (C) sinks and reduce C emissions from land use activities. Residual materials with fertilizing capacity can be used to reconstruct severely degraded soils and recreate a sustainable vegetation cover, leading to reductions in atmospheric CO 2 levels. We studied the temporal dynamics of CO 2 sequestration potential in soils reconstructed with 1200 Mg ha−1 biosolids along a young chronosequence ranging from 0 to 7 years after initiating reclamation of a decommissioned asbestos mine in southern Québec, Canada. We measured in situ soil CO 2 fluxes, soil C pools and soil physicochemical properties. Since bacterial communities are highly responsive to soil physicochemical properties, we also analyzed both their diversity and community structure. The age since soil reclamation did not have a clear effect on soil properties, but it exerted greater control over soil C fluxes and soil bacterial community diversity and structure. Our results suggest large C fluxes to the atmosphere within the first year following soil reconstruction, but soils constitute a stable C pool thereafter. [ABSTRACT FROM AUTHOR]

• Tree planting on degraded land has been identified as an effective carbon capture strategy. • Unclear how associated restoration treatment influence carbon sequestration. • Tree carbon pool increased with greater restoration effort. • Existing site characteristics influence carbon sequestration potential. • Land managers must balance restoration cost with carbon sequestration. Landscape carbon storage is a key component of climate change mitigation. Tree planting on degraded land has been identified as an effective carbon capture strategy, but it is unclear how various associated restoration treatments influence carbon sequestration. In this study, we measured carbon pools in jack pine (Pinus banksiana Lamb.) stands subject to different restoration treatments within severely damaged upland areas in the metal mining region of Sudbury, Ontario, Canada. Treatments included: i) soil amendment (liming, fertilizing and grass/legume seeding) followed by jack pine planting, ii) jack pine planting alone, iii) soil amendment only, and iv) untreated plots with some natural regeneration as a result of improving air quality in the region. Twenty-four years after the initial treatments, we measured the carbon storage in coarse and fine woody debris, herbs, shrubs, forest floor (LFH), mineral soil, and trees. The carbon pool in planted trees was 1.5 times higher in plots when soil amendments were applied. This increase in the tree carbon pool was the result of greater carbon sequestration per individual jack pine tree rather than changes in tree density or arrival of new species. Similarly, naturally regenerated white birch (Betula papyrifera Marshall) in the amended plots stored 1.7 times more carbon than white birch in the untreated plots. Tree planting proved essential on this landscape with natural tree regeneration rates very low even 50 years after local pollution was massively reduced. However, tree planting surprisingly did not significantly affect total carbon storage in these exposed upland sites. Total ecosystem carbon varied from 21.4 Mg ha−1 to 124.5 Mg ha−1 across all plots (mean of 67.6 ± 4.8 Mg ha−1) but no statistically significant differences were observed among the treatments. Soil organic carbon (SOC) proved to be the largest carbon pool across plots and stored on average 66% of total ecosystem carbon. However, at this early stage the restoration treatments had no influence on SOC pools on this highly degraded landscape, which still appears to be severely affected by ongoing erosion of surface soil and metal contamination. The restoration treatment also did not significantly affect the understory or downed woody debris carbon pools. This study demonstrates that the current restoration treatments used in Sudbury do influence the amount of carbon sequestrated mainly through tree restoration on this industrially degraded landscape, but long-term storage potential is still limited by poor soil conditions. [ABSTRACT FROM AUTHOR]