Carbon Stocks in Soils Based on the State Forest Inventory Data

The main organic carbon stocks in the predominantly boreal forests of Russia are contained in the soil pool. Quantitative estimates of soil pool carbon stocks vary considerably. This is due to the high temporal and spatial variability of the organic carbon content in soils, the lack of empirical data for a number of regions, the difference in approaches to assessing soil carbon and the density of soil horizons, the thickness of the soil layer taken into account, the inclusion of forest litter carbon stocks, the peat layer, etc. In 2020, the 1st cycle of the State Forest Inventory in Russia was completed using a selective statistical method. Forest inventory characteristics, environmental indicators and information on forest growth conditions have been obtained for 69.1 thousand permanent sample plots. The limited availability of field descriptions of soils necessitates the testing of an integrated approach to using the State Forest Inventory data in the software environment of geographic information systems in combination with open-access digital resources to assess carbon stocks in the soil pool. A methodology for quantitative assessment of carbon stocks in the forest soil pool has been developed and experimentally tested. The proposed methodology includes: 1) geo-referencing of sample plots; 2) bringing the initial data of the State Forest Inventory on soil types to a standard classification; 3) using the digital resources of the World Data Center for Soils (SoilGrids) to obtain reference average carbon stocks on the network of sample plots surveyed during the State Forest Inventory; 4) calculating the total carbon stock in the soil pool of forest lands based on the average carbon stocks of SoilGrids and areas of standard soil types based on the data of the State Forest Inventory. The experimental testing has been carried out using the Republic of Karelia as an example. The sample size has been 667 permanent sample plots. According to the results of the study, the predominant complex of soil types – illuvial-ferruginous and illuvial-humus podzols (without division), illuvial low- and high-humus podzols – covers an area of 7.28 mln ha. The total carbon stock in the 0–30 cm soil layer for the forest lands of the Republic of Karelia is estimated at 773.9 Mt C with an average of 79.1 t C/ha.