Overview

Soils store about three times as much carbon as does terrestrial vegetation (Schlesinger, 1986). About 27 per cent of this carbon is found in tundra and boreal forest ecosystems. Since a large part of Canada lies within these regions, a significant portion of the world's soil carbon occurs in Canadian territory. The grassland region, which includes arid, transitional and subhumid grassland, stores considerably less carbon than the more northern regions.

On the whole, little published data exist on the amount of organic carbon in Canadian soils. To address this deficiency and obtain an accurate estimate based on soil measurements, the Soils Carbon Project was initiated in 1991. With the use of a variety of techniques and a geographical information system (GIS), a database was compiled on Canadian soils to calculate the amount of organic carbon in various soils. This database provided a means for determining the relationships between the amount of soil carbon and its attributes (including soil drainage, mode of deposition of parent soil material, broad vegetation cover and land use). Carbon values were derived for all soil areas in Canada. The soil carbon mass and contents were initially determined based on the individual soil components. The database was designed so that carbon values for the upper 30 cm of both mineral and organic soils could be determined separately.

Canada is divided into 18 ecoclimatic provinces within six broader ecoclimatic provinces, specifically, the arctic, subarctic, boreal, cordilleran, temperate and grassland. The greatest surface and total carbon content was found in the boreal ecoclimate province, with around 11.8 kg/m² of surface carbon and 50.5 kg/m² of total carbon. This total was closely followed by the subarctic ecoclimatic province with around 11.0 kg/m² of surface carbon and 50.4 kg/m² of total carbon. The grasslands fall a distant sixth, at 7.2 kg/m² of surface carbon and 12.2 kg/m² of total carbon.

The largest surface carbon mass again occurred in the boreal ecoclimatic province with around 26.1 Gt. This was followed by the subarctic ecoclimatic province with 16.6 Gt, and the arctic ecoclimatic province with 16.2 Gt. Together, these three ecoclimatic provinces compromise 82 per cent of the surface carbon mass in Canada. The largest total carbon mass also occurred in these three ecoclimatic provinces. The boreal region led with 111.8 Gt, followed by the subarctic region with 75.7 Gt, and the arctic region with 43.0 Gt, which combined contain approximately 88 per cent of the total carbon mass for Canada. The grassland province, at 3.3 Gt, falls a distant sixth.