Carbon and nitrogen pools and mineralization rates in boreal forest soil after stump harvesting

Abstract

25The use of forest-derived biomass has steadily increased in Finland and Sweden during the 26 past decades leading to more intensive forest management practices in the region, such as 27 whole-tree harvesting, both above-and belowground. Stump harvesting results in a direct 28 removal of stump and coarse-root carbon (C) from the stand and can cause extensive soil 29 disturbance, which in turn can result in increased C mineralization. In this study, the effects 30 of stump harvesting on soil C and nitrogen (N) mineralization, and soil surface disturbance 31 were studied in two different clear-felled Norway spruce (Picea abies) sites in Central 32Finland. The treatments were whole-tree harvesting (WTH, removal of stems and logging 33 residues), and WTH and stump harvesting (WTH+S). Both sites, Honkola (2 stands) and 34Haukilahti (6 stands) were mounded. In both treatments, soil samples were taken from 35 different soil layers down to a total depth of 20 cm from (i) mounds, (ii) undisturbed soil and 36 (iii) pits. The sampling was performed 11-12 years after treatments. Soil C and N 37 mineralization rates were determined in laboratory incubation experiments. In addition, total 38 C and N pools (g m -2 ) were estimated for each disturbance class and soil layer. Soil C and N 39 pools tended to be lower following stump harvesting, but no statistically significant treatment 40 effect was detected. Stump harvesting increased soil mixing as indicated by a significant 41 decrease in C concentration in the mound disturbance class. There was no significant effect 42 of stump harvesting on soil C mineralization rates. A combination of mineralization rates and 43 soil pool data showed that field C mineralization (g CO2-C m -2 yr -1 ) did not significantly 44 differ between stands where stumps were removed or were retained. Further, stump 45 harvesting did not seem to have any stimulating effect on soil CO2 efflux 11-12 years after 46 treatment. 47 48 49 3

Stump harvesting for bioenergy: A review of climatic and environmental impacts in northern Europe and America

“…Longer-term effects of stump harvesting on heterotrophic respiration (R h ) were studied in Finland 11-12 years after clearcutting (Kaarakka et al, 2016). R h rates were determined in mounds (with a double humus layer), pits (lacking humus layer), and undisturbed soil, but no significant effect of stump harvesting, in comparison with patch scarification, could be detected.…”

Transient trade‐off between climate benefit and biodiversity loss of harvesting stumps for bioenergy

“…In this study, we did not account for any feedbacks between stump harvesting and soil carbon turnover through enhanced soil disturbances, although stump extraction might lead to soil mixing, compaction, temperature increases, wetter soils and damage on decomposers (Walmsley & Godbold, ). These different effects might lead to both faster and slower decomposition rates, but still, field experiments indicate no significant net effects on soil C mineralization rates in boreal forests (Kaarakka et al ., ). In case of increased soil carbon turnover, the negative climate effects might be long‐lasting, though (Ortiz et al ., ).…”

Nitrogen addition enhances nitrogen but not carbon mineralization in aggregate size fractions of soils in a Pinus massonia plantation

“…Soil moisture was adjusted at 60% of the field capacity. Levels of CO 2 absorbed in NaOH, as measured by total oxidizable C, were used to calculate Soil Organic Carbon (SOC) mineralization (Rabbi et al, 2014;Kaarakka et al, 2016). These soil fractions were incubated in an incubator at 25°C for 24 days.…”

“…In subtropical forest ecosystems, stability and primary productivity of the ecosystem are constrained by the effectiveness of nitrogen (N, Du et al, 2021), Over the past century, there has been an approximately tenfold increase in N input into these ecosystems by atmospheric deposition, significant augmenting N level in the soil (Galloway et al, 2004;Peñuelas et al, 2012). The process of N mineralization plays a crucial role in breaking down soil organic N into inorganic N, thereby critically regulating the N balance within forest ecosystems (Kaarakka et al, 2016). Atmospheric N deposition can modify soil organic N mineralization rates through its effect on inorganic N stocks (Baldos et al, 2015), and it can also impact overall N mineralization by impacting stoichiometric ratios (Gao et al, 2020).…”