World’s Soil Resources

where the drainage in the 1960’s of areas previously classified as peatland caused the SOC content to fall to 7.5
percent (Panagos et al., 2013). Without further adjustments of SOC stock estimates to take account of local
changes in the factors that influence SOC, no clear timestamp can be attached to the global estimates. This
lack of a clear timestamp of SOC stocks is of consequence when estimating temporal changes in SOC stocks.
Estimates of changes in SOC stock therefore concentrate on modelling variations in SOC from changes in land
use and cover.
6.2.3 | Spatial distribution of SOC
Different methods of combining point data from soil profiles with soil spatial layers and ancillary ecological
data can be applied to derive spatial estimates of SOC stocks (Kern, 1994). SOC density and stock estimates
from soil profile data were combined with spatial data of major ecosystems by Post et al. (1982). The total SOC
stocks for all life zones to a depth of 1 m was 1 395 Pg of SOC. A combination of soil profile data with ancillary
information on climate, vegetation and land use was used by Jobbágy and Jackson (2000) to estimate SOC
stocks in 11 biomes. The estimates for the biomes were further divided into increments of 1 m soil depth and
of 20 cm for the first meter. The distribution of SOC stocks by ecological regions has also been presented, for
example by Amundson (2001), who used life zones as the study unit. Eglin et al. (2010) used the SOC stock
estimates to a depth of 3 m from Jobbágy and Jackson (2000) and modified SOC stocks in permafrost areas
(Tarnocai et al., 2009). These SOC stock estimates were combined with estimates provided by the IPCC (IPCC,
2000) of C in vegetation to derive estimates of C in soil and biomass for 10 biomes, with an explicit class for
peatlands. A step towards adding a temporal dimension to spatial SOC stock estimates, assessing historical
and future trends, was made possible by the availability of SOC models. Combining the models with historic
land use and climate data has allowed estimation of SOC stocks with a timestamp and with regional variations
(Eglin et al., 2010; Schmidt et al., 2011).
Carré et al. (2010) produced estimates of SOC stocks and density using climate data, IPCC methodology and
the Harmonized World Soil Database. The results by IPCC Climate Region are presented in Table 6.1.
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