Soil carbon stock increases in the organic layer of boreal middle-aged stands

Abstract

Abstract. Changes in the soil carbon stock can potentially have a large influence on global carbon balance between terrestrial ecosystems and atmosphere. Since carbon sequestration of forest soils is influenced by human activities, reporting of the soil carbon pool is a compulsory part of the national greenhouse gas (GHG) inventories. Various soil carbon models are applied in GHG inventories, however, the verification of model-based estimates is lacking. In general, the soil carbon models predict accumulation of soil carbon in the middle-aged stands, which is in good agreement with chronosequence studies and flux measurements of eddy sites, but they have not been widely tested with repeated measurements of permanent plots. The objective of this study was to evaluate soil carbon changes in the organic layer of boreal middle-aged forest stands. Soil carbon changes on remeasured sites were analyzed by using soil survey data that was based on composite samples as a first measurement and by taking into account spatial variation on the basis of the second measurement. By utilizing earlier soil surveys, a long sampling interval, which helps detection of slow changes, could be readily available.The range of measured change in the soil organic layer varied from −260 to 1260 g m −2 over the study period of 16-19 years and 23 ± 2 g m −2 per year, on average. The increase was significant in 6 out of the 38 plots from which data were available. Although the soil carbon change was difficult to detect at the plot scale, the overall increase measured across the middle-aged stands agrees with predictions of the commonly applied soil models. Further verification of the soil models is needed with larger datasets that cover wider geographical area and represent all age classes, especially young stands with potentially large soil carbon source.

Increasing soil carbon stocks in eight permanent forest plots in China

“…than one-half of the vegetation C uptake rate in China's forests (702.0 kg C ha −1 yr −1 ) (Guo et al, 2013;. This result suggests that China's forest soils have contributed to a negative feedback to climate warming during the past 2 decades, rather than the positive feedback predicted by coupled C-climate models (Cox et al, 2000;He et al, 2016;Wang et al, 2018).…”

Global estimates of boreal forest carbon stocks and flux

“…Yet quantifying both storage and flux from permafrost in the context of the boreal is confounded by datasets created to address issues across the northern cryosphere, rather than separating Arctic/tundra from strictly boreal deposits (McGuire et al, 2010;Grosse et al, 2011) (but see Tarnocai, 1998Tarnocai, , 2000. Likewise soil carbon, which in the boreal accounts for at least three times the carbon that is stored in vegetation (Malhi et al, 1999), is often determined using model predictions rather than repeated soil measurement over sufficient time sequences at permanent sample plots (Häkkinen et al, 2011). Those assessments of soil carbon stores available are frequently made to only ≤ 1 m depth and consequently ignore any stores below (Jobbágy and Jackson, 2000;Seedre et al, 2011), although soils below 1 m are considered by many (e.g., Deluca and Boisvenue, 2012) not to contain substantial amounts of carbon (but see Tarnocai et al, 2009;Jorgenson et al, 2013;Kuhry et al, 2013;Hugelius et al, 2014).…”

Mapping Above- and Below-Ground Carbon Pools in Boreal Forests: The Case for Airborne Lidar

“…Boreal forest soils represent a large C pool characterized by high spatial and temporal variations [ 15 , 16 ], making accurate assessments of soil C expensive and labor intensive. For purposes such as investment planning in forest C offset projects, the variability and rate of soil C storage and accumulation is a major challenge.…”