Effects of deforestation on ecosystem carbon densities in central Saskatchewan, Canada

Ecosystem carbon densities (aboveground vegetation plus soil organic carbon (SOC) to 45 cm depth) were compared for forested and deforested sites on hummocky glacial till landforms in central Saskatchewan. Six forest sites in Prince Albert National Park, six pasture sites in or near the Cookson Community Pasture, and six privately owned cultivated fields were sampled across a 30 000 ha study area (53°34ʹN, 106°20ʹW). The median ecosystem C density for forests (158 Mg C ha^-1) was significantly greater (P<0.05) than the median for pastures (63 Mg C ha^-1) and the median for cultivated fields (81 Mg C ha^-1). For soil organic carbon alone, significant differences were not detected between forested and deforested sites. The range for SOC density across the study area was 51 Mg C ha^-1 for natural forest sites, 54 Mg C ha^-1 for pastures and 92 Mg C ha^-1 for cultivated fields. Spatial variation in SOC densities within each treatment group precluded detection of land-use effects on SOC densities (expected to be =>25 Mg C ha^-1) with this research design. SOC may have been elevated at sites with shallower groundwater, but further research is required to confirm this and to identify the responsible processes. Differences in ecosystem C densities between the forested and deforested sites were primarily the result of differences in vegetation biomass. Median live plus dead vegetation C density for the forest group was 60 Mg C ha^-1 greater than the pasture group (P<0.05) and 56 Mg C ha^-1 greater than the cultivated group (P<0.15). Including estimated C in coarse roots and lesser vegetation at the forest sites would increase these differences by approximately 15 Mg C ha^-1. Accounting for disturbance processes such as forest fires, differences in vegetation carbon between forested and deforested sites in this study area are estimated to vary between 30 to 75 Mg C ha^-1 over time. Continued agricultural expansion within the study area would result in losses of at least 30 Mg C ha^-1. Recent ratification of the Kyoto protocol by Canada provides an incentive to curtail deforestation and initiate reforestation actions. Future reforestation with trembling aspen dominated vegetation in central Saskatchewan has the potential to sequester 30–75 Mg C ha^-1 over the next 50–100 years. However, legislative protection or strong financial incentives will be required to secure longterm carbon gains through reforestation.