Underestimation of boreal forest soil carbon stocks related to soil classification and drainage

Abstract

Soil organic carbon (C), accumulated over millennia, comprise more than half of the C stored in boreal and temperate forest landscapes. We used the Norwegian national forest inventory and soil survey network (n = 719, no deep organic soils) to explore the validity of a deterministic model representation of this pool (Yasso07). We statistically compared simulated and measured soil C stocks and related differences (measured -simulated) to site factors (drainage, topography, climate, vegetation, C-to-N ratio, and soil classification). Median C stocks were 5.0 kg C·m −2 (model) and 14.5 kg C·m −2 (measurements). Soil C differences related to site factors (r 2 of 0.16 to 0.37). For Brunisols, Gleysols, and wet Organic soils, differences related primarily to topographic wetness. For Regosols, Podzols, and Dystric Eluviated Brunisols, they related to climate, profile depth, and, in some cases, drainage class and site index. We argue that soil moisture regimes in our study area overrule tree productivity effects in the determination of soil C stocks and present conditions for soil formation that the model cannot (and does not explicitly) account for. These are processes such as humification and podsolization that involve eluviation and illuviation of dissolved organic C (DOC) with sesquioxides to form spodic B horizons and carbon enrichment due to hampered decomposition in frequently anoxic conditions.Key words: drainage, national forest inventory (NFI), SOC simulation, soil classification, soil-forming factors, soil moisture regime, soil survey, podsolization, Yasso07. Résumé :Le carbone (C) organique du sol accumulé au fil des millénaires correspond à plus de la moitié du C stocké dans les paysages forestiers boréaux et tempérés. Nous avons utilisé l'inventaire forestier national norvégien et le réseau d'inventaire des sols (n = 719, aucun sol organique épais) pour étudier la validité d'une représentation de ce réservoir (Yasso07) à l'aide d'un modèle déterministe. Nous avons statistiquement comparé les stocks de C du sol simulés et mesurés, et relié leurs différences (mesurés -simulés) à des caractéristiques de la station (drainage, topographie, climat, végétation, rapport de C à N et classification du sol). Les stocks médians de C atteignaient 5,0 (simulé) et 14,5 (mesuré) kg C·m -2 . Les différences de C du sol étaient reliées aux caractéristiques des stations (r 2 de 0,16 à 0,37). Pour les brunisols, les gleysols et les sols organiques humides, les différences étaient surtout reliées à l'humidité topographique. Pour les régosols, les podzols et les brunisols dystriques éluviés, les différences étaient reliées au climat, à la profondeur du profil et, dans certains cas, à la classe de drainage et à l'indice de qualité de station. Nous avançons que le régime d'humidité du sol de notre aire d'étude est un facteur plus important que les effets de la productivité ligneuse pour déterminer les stocks de C, et qu'il engendre des conditions de formation des sols dont le modèle ne peut tenir compte et ne tient pas ...

Patterns and predictors of soil organic carbon storage across a continental-scale network

“…3). Importantly, few sites (whether NEON or otherwise) span the full range of drainage classes, and while each of the three we assessed shows a grossly similar qualitative trend, not one shows the clearly significant pattern that we observed at the continental scale, or others have reported at regional and continental scales (Dalsgaard et al 2016;Davidson 1995;Davidson and Lefebvre 1993;Wills et al 2013). Thus, expecting drainage sequences to align neatly with SOC stocks on any landscape is unwarranted, despite the convincing pattern from the largescale dataset, which has been documented in individual site-level studies elsewhere (Raymond et al 2011;Richardson and Stolt 2013;Webster et al 2008).…”

Evaluation of organic carbon stocks in mineral and organic soils in Lithuania

“…Carbon sequestration in forest soils plays an important strategic role (Jobbágy & Jackson, 2000). Boreal forest soils, which accumulate up to five times more organic carbon (OC) than plant biomass or about 85% OC in forest ecosystems, are a reservoir for long-term storage of boreal C and a significant contributor to global C storage (Dalsgaard et al, 2016;Jones et al, 2009;Martin et al, 2005;Pan et al, 2011). In European forest soils, SOC accumulation is approximately 1.5 times higher than in tree stem biomass (de Vries et al, 2003).…”

Evaluating the terrestrial carbon dioxide removal potential of improved forest management and accelerated forest conversion in Norway

“…Where labile groups are chemically defined (by solubility; values are provided in Table S1) and constrained by empirical mass loss, the parameters determining humus dynamics are primarily constrained by soil C stock data. Application to Norwegian conditions is further described in Dalsgaard, Astrup, et al (2016) and Dalsgaard, Lange, et al (2016).…”

“…Each plot is initialized by a spin‐up to equilibrium in five pools (e.g., the three labile + insoluble + humus) using the average litter input 1990–2016 grouped by site index and dominant tree species (Table S6). Forested plots are then subject to a pre‐simulation or “backcast” of 30 years (6 × 5 year time steps) as described in Dalsgaard, Astrup, et al (2016) and Dalsgaard, Lange, et al (2016). This backcast is based on land use prior to NFI plot establishment and national standards for harvest volumes and ages for the relevant time period.…”