Abstract
Using residual biomass from forest harvesting to produce energy is viewed increasingly as a means to reduce fossil fuel consumption. However, the impact such practices on soil and future site productivity remains a major concern. We revisited 196 forest plots that were subject to either whole-tree (WTH) or stem-only (SOH) harvesting 30 years ago in the boreal forest in Quebec, Canada. Plots were stratified by four soil regions grouped by so-called ‘soil provinces’. Soil analyses indicated that after 30 years, the forest floor of WTH sites had smaller pools of N (−8%), exchangeable Ca (−6%) and exchangeable Mn (−21%) and a higher C/N ratio (+12%) than that of SOH sites. Mineral soil responses to the two harvesting intensities differed among soil provinces. In the two coarse-textured granitic soil provinces, organic matter, organic carbon, and nitrogen pools over the whole solum (0–60 cm soil depth) were at least 28% smaller after WTH than after SOH. Site productivity indicators followed differences between soils and were lower after WTH than after SOH in the two granitic soil provinces. The study shows that soil characteristics greatly influence a soil’s sensitivity to increased forest biomass harvesting in the long term.
Highlights
The development of bioenergy and renewable energy technologies to shift away from the use of high-emission fossil fuels is key to achieving reductions in greenhouse gas emissions
In these two soil provinces similar amounts of biomass were harvested, but about half mineralomass were exported by stem-only harvesting (SOH) as compared to whole-tree harvesting (WTH). This is due to the larger basal area—and greater bole biomass—in sites subjected to SOH compared to WTH (Supplementary Material Table S1)
Our results showed smaller soil organic matter (OM) and organic C pools in WTH sites as compared to SOH sites, but only in the two granitic soil provinces characterized by a coarser soil texture, even though exported biomass was similar
Summary
The development of bioenergy and renewable energy technologies to shift away from the use of high-emission fossil fuels is key to achieving reductions in greenhouse gas emissions. The various transition pathways explored so far to limit the rise of global mean temperature abundantly rely on bioenergy due to its multiple roles in the decarbonization of energy [1]. Residual biomass generated by forest harvesting in public forests in Quebec amounted to 8779 green Mg in 2018–2019, of which only 8.6% was attributed to users [2]. Forest biomass converted into bioenergy primarily for the targeted substitution of greenhouse gas-intensive materials or energy is part of various scenarios to mitigate the rise of atmospheric CO2 , by the Quebec forestry sector for example [3]. Among the methods used to harvest wood, whole-tree harvesting (WTH), which encompasses several methods in which all parts of the tree above the stump are harvested, and stem-only harvesting (SOH) in which only the merchantable stems are harvested, are generally used to analyze the effects of more intense harvesting, such as those for biomass production
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