Elevation gradient drives distribution of soil carbon in a semiarid of British Columbia

A sequence of Brown, Dark Brown and Black Chernozems spanning a 600 m elevation gradient in a semiarid bunchgrass ecosystem (Lac du Bois Grassland) near Kamloops, British Columbia was first described in 1961. More soil organic carbon (SOC) at higher elevations along the sequence was attributed to increasing effective precipitation with increasing elevation. Since the 1961 study, plant community composition has shifted toward the desired climax community due to improved livestock management instituted in the 1970s; however, changes in soil carbon stocks remain unknown. The objective of this study was to quantify SOC and soil inorganic carbon (SIC) stocks using the same site selection criteria as used in 1961. SOC stocks (kg m-2 +/- SD; 0-60 cm) were similar for Brown (5.73 +/- 1.7) and Dark Brown Chernozems (5.87 +/- 0.76) but increased sharply (10.11 +/- 2.5) for the higher elevation Black Chernozems. SIC increased with depth in all three soil zones, representing 33%-50% of total C from the 30-60 cm soil depth. To evaluate changes in SOC (0-20 cm) from the 1961 measurements, three different approaches for calculating SOC stocks were used based on the inclusion or exclusion of coarse fragments. Results varied across the three soil zones from no change to a 20% increase in the Brown, an increase of 7% to a reduction of 26% in the Dark Brown, and a decrease of 12% to 35% in the Black soil zone. Information about soil coarse fragments and the distribution of SOC and SIC stocks within the soil profile is crucial for accurate comparisons across studies or resampling events.