Effectiveness of soil N availability indices in predicting site productivity in the oil sands region of Alberta

Background and aims: Quantitative relationships between soil N availability indices and tree growth are lacking in the oil sands region of Alberta and this can hinder the development of guidelines for the reclamation of the disturbed landscape after oil sands extraction. The aim of this paper was to establish quantitative relationships between soil N availability indices and tree growth in the oil sands region of Alberta. Methods: In situ N mineralization rates, in situ N availability measured in the field using Plant Root Simulators (PRS™ probes), laboratory aerobic and anaerobic soil N mineralization rates, and soil C/N and N content were determined for both the forest floor and the 0-20 cm mineral soil in eight jack pine (Pinus banksiana Lamb.) stands in the oil sands region in northern Alberta. Tree growth rates were determined based on changes in tree ring width in the last 6 years and as mean annual aboveground biomass increment. Results: Soil N availability indices across those forest stands varied and for each stand it was several times higher in the forest floor than in the mineral soil. The in situ and laboratory aerobic and anaerobic soil N mineralization rates, soil mineralized N, in situ N availability measured using PRS probes, soil C/N ratio and N content in both the forest floor and mineral soil, as well as stand age were linearly correlated with tree ring width of jack pine trees across the selected forest stands, consistent with patterns seen in other published studies and suggesting that N availability could be a limiting factor in the range of jack pine stands studied. Conclusions: In situ and laboratory aerobic and anaerobic N mineralization rates and soil C/N ratio and N content can be used for predicting tree growth in jack pine forests in the oil sand region. Laboratory based measurements such as aerobic and anaerobic N mineralization rates and soil C/N ratio and N content would be preferable as they are more cost effective and equally effective for predicting jack pine growth.