Measurements and models –a comparison of quantificationmethods for SOC changes in forestsoils

• The Swedish UNFCCC1-reporting of the LULUCF2-sector is based on methods incompliance with the “Good practice” as described by the Intergovernmental Panelon Climate Change (IPCC). Biomass and soil inventory data from the SwedishInventory of Forests is the major source of information used to quantify changes inthe various carbon pools on forest land. Even if the reported uncertainties in soilcarbon changes are small from a statistical perspective, they are large in relation tothe total Swedish emissions of green house gases. This is due to the fact that thesoil carbon pool is so large, that even small and statistically non-significantchanges may have an impact on the Swedish CO2 balance. Sampling based methodsmay also result in considerable inter annual variations that may look conspicuousin the reporting. Because of the uncertainty and inter annual variations therehas been a discussion on the methods used and if there are possibilities to lower theuncertainty and to get more stable estimates of soil carbon changes by combiningmeasurements and models. In this study results from the two soil carbon models,Yasso07 and Q, were compared with repeated measurements of the soil inventoryduring the years 1994 to 2000. Soil carbon fluxes were simulated with the twomodels from 1926 to 2000 with Monte Carlo methodology to estimate uncertaintyranges. The results from the models agreed well with measured data. The simulationsof Yasso07 and Q resulted in a soil organic carbon stock in year 2000 of1600 Mton C and 1580 Mton C, respectively while the measured carbon pool was1670 Mton C. The annual change in soil organic carbon varies substantially betweenthe three methods mainly due to different assumptions regarding annualclimate variation. However, the five year averaged mean of annual soil organiccarbon change for the two periods 1994-1998 and 1996-2000 indicate the size anddirection of the estimated annual changes agree reasonable well. The mean annualchange for the two periods was for the Q-model 5.5 Mton C yr-1 and 5.6 Mton C yr-1with a confidence interval of 2.1-10.7 Mton C yr-1, and for the Yasso07-model 3.7Mton C yr-1 and 0.9 Mton C yr-1 respectively with a confidence interval rangingbetween -5 to 12.6 and -7 to 9.8 Mton C yr-1 respectively. The mean annual changefor the two periods estimated using NFI-data was 1.6 M ton C yr-1 and 2.5 M ton Cyr-1 with a standard error of 2 The general conclusion drawn from this study is thatboth sampling and the models Yasso07 and Q are possible tools to predict the soilorganic carbon accumulation and annual changes for Swedish forest soils. Theestimates based on measurements as well as the modelled results indicate an increasein carbon stocks in Swedish forest soils. This study does not support achange of method from inventory to model predictions. However, the agreementbetween the methods shows that the models are suitable as a complement to othersoil carbon estimation methods. They are particularly useful for projections and werecommend a further development of the modelling tools.

Subject headings

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Environmental Sciences (hsv//eng)

LANTBRUKSVETENSKAPER  -- Annan lantbruksvetenskap -- Förnyelsebar bioenergi (hsv//swe)

AGRICULTURAL SCIENCES  -- Other Agricultural Sciences -- Renewable Bioenergy Research (hsv//eng)

LANTBRUKSVETENSKAPER  -- Lantbruksvetenskap, skogsbruk och fiske -- Skogsvetenskap (hsv//swe)

AGRICULTURAL SCIENCES  -- Agriculture, Forestry and Fisheries -- Forest Science (hsv//eng)

Keyword

SMED (Svenska MiljöEmissionsData)

SMED (Svenska MiljöEmissionsData)

Luft

Luft

Clean air

Frisk luft

Hazardous substances

Publication and Content Type

vet (subject category)

rap (subject category)