Winter planting of frozen black spruce seedlings was studied in a northern Alberta wetland supported by the Oil Sand Leadership Initiative (OSLI) Land Stewardship Working Group, comprised of ConocoPhillips Canada, Shell Canada, Statoil, Suncor Energy Inc., Nexen Inc., and Total E&P Canada. The major objective is to address accessibility issues in oil sands wetland restoration processes. Close to 500 1+0 black spruce frozen container seedlings were winter-planted at a small wetland area on February 22, 2011 at -17°C immediately after a total of 260 mounds were generated. On each mound two seedlings were planted at either 4 cm or 8 cm deep, i.e. the depth from the top of seedling plug to soil surface. Another group of 240 black spruce seedlings from the same stock was spring-planted in May 25, 2011 after operational thawing. Seedlings’ survival, first year new height growth, and damages to terminal bud and side branch were measured in September 2011.
More than 94% of the seedlings survived in all planting treatments although the seedlings winter-planted to 4 cm had 4-5% less survival rate. There was no difference in survival between the seedlings winter-planted to 8 cm and spring-planted. Winter planting induced substantial damage to terminal bud (46%) and branch (58-86%) although planting to 8 cm resulted in less branch damage. All seedlings had a very healthy height growth in 2011 (10-20 cm) and there was no difference between the different planting depths although the spring-planted grew 4-7 cm more.
The results suggest that winter-planting of frozen black spruce container stocks is a feasible option for northern Alberta wetlands although similar trials should be conducted before other species can be applied. A planting depth of more than 8 cm is beneficial and critical to enhance the performance of the winter-planted seedlings. Our findings also suggest that a temperature of -15°C may be a safe operational threshold for transporting and planting frozen black spruce container stocks. Although this study has proved the feasibility of winter planting, significant improvement in winter-planting performance may also be achieved through reducing seedling bud damage (e.g. better stress tolerance, different seedling sizes and planting depths) and increasing mound stability after site preparation.