Limiting factors for lodgepole pine (Pinus contorta) and white spruce (Picea glauca) growth differ in some reconstructed sites in the Athabasca oil sands region

Peat-mineral soil mix (PMM) over tailings sand (TS) or overburden (OB) is a commonly used prescription for oil sands reclamation. The TS and OB (the substrates) often have unfavorable conditions such as high salinity, soil compaction, low nutrient availability in OB, and low nutrient and water availabilities in TS, which may limit tree growth. The objective of this study was to identify limiting factors for growth of lodgepole pine (Pinus contorta) on PMM over TS and white spruce (Picea glauca) on PMM over OB in the Athabasca oil sands region, Alberta, Canada. In the pine sites, mean annual growth of height (HG), diameter at breast height (DBHG) and aboveground biomass (ABG) were significantly correlated with volumetric water content (VWC) in PMM and foliar δ13C in current-year needles. Sites with high productivities had the lowest foliar δ13C relative to sites with low and medium productivities. The VWC and dissolved organic carbon (DOC) together explained 80% of the variation in both the current annual increment of height (HI) (p = 0.007) and aboveground biomass (ABI) (p = 0.008). In the spruce sites, foliar potassium (K) and foliar and soil nitrogen (N) concentrations were positively correlated with HG, DBHG and ABG, consistent with patterns in K and inorganic N (the sum of NH4+-N and NO3−-N) concentrations in PMM in those sites. Soil electrical conductivity (EC) and bulk density (Db) were greater in low than in medium and high productivity sites. The Db and inorganic N concentration together explained 67% of the variation in HI (p = 0.037), while Db and EC together explained 79% of the variation in ABI (p = 0.009). In conclusion, lodgepole pine trees planted on PMM over TS sites were limited by low water availability, while low soil N availability and high salinity limited the growth of white spruce trees planted on PMM over OB sites. Reclamation practices need to address water and nutrient limitations to ensure the success of reclaiming disturbed areas in the oil sands region.