Current free growing standards in British Columbia stipulate that crop trees must be free of competing vegetation. This is often achieved at great economic cost, as well as at a cost to landscape level biodiversity and stand structure variation. The relative impacts of competing vegetation on free-growing aged spruce crop trees in the sub-boreal and boreal mixedwood forests of BC are investigated. Temporary sample plots were installed in the sub-boreal near Mackenzie, and in the boreal forest near Fort Nelson and Fort St. John. Growth of spruce was measured under varying densities of aspen and birch, respectively. Impacts from deciduous vegetation on diameter growth of spruce appear to be minimal up to a threshold of 5000 to 6000 stems per hectare of aspen or birch. Long-term timber volume and conifer densities projected in TIPSY and TWIGS, two growth models, suggest the stands growing with varying densities of deciduous stems are above expected diameters for their age. Concerns for volume loss in these stands over the rotation due to competition from non-crop vegetation may not be valid.
Menounos, Kimberly, Hawkins, Chris D.B.; Harper, George J.; Kabzems, Richard. 2005. Managing northern mixedwood stands to sustainably maximize productivity and minimize costs. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report