- Stiell, W.M.
- Canadian Forestry Service, Petawawa National Forestry Institute
Understory 55-year-old white pine in mixedwood stands were released in 1971 from an (ca. 80-year- old) overstory of intolerant hardwoods using wheeled skidders in a commercial logging operation. The main aim of the study was to increase the growth and yield of white pine for sawlogs over the following 20 to 30 year period by releasing suppressed pine. Growth of released, healthy white pine was assessed after logging for a range of stand densities (basal areas of 6.9, 11.5, 16.1 m2 hr^-1) using suitable control plots and a randomized complete block design with five replicates. Plots were remeasured l0 and 20 years after treatment. By harvesting, much of the natural mortality associated with these stands over the 20 year-period was utilized. Growth responses associated with overstory release were highly significant and demonstrated an 80% increase in sawlog volume increment for treated stands after 20 years. Herb diversity was higher in treated stands and browse potential was not affected. However, white pine regeneration was unacceptably low in all cases. Overstory release increased the natural rate of succession in these stands, but without further management activities or wildfire, the study area will revert to the economically lower-valued hardwoods.