A study was established in 1994 in the SBSdw2 variant of the Cariboo-Chilcotin region of the Southern Interior Forest Region to investigate the effects of removing aspen in 50 or 100 cm radii around crop lodgepole pine versus broadcast removal or no treatment. The primary objective of the study was to assess whether the free-growing criterion (current in 1994), which specified that no overtopping vegetation could be present within a 1 m radius around crop trees, was appropriate in pine-aspen stands, or whether a 50 cm radius zone would be adequate.
After 9 years, during which treatments were maintained annually, there were no differences in pine survival or growth between the 50 and 100 cm radius treatments. Even in the untreated control, there was no mortality as a result of vegetation competition, and neither were there vigour losses. There also were no significant differences in pine stem diameter or height as a result of any of the treatments, but height:diameter ratio (HDR) was significantly lower in the broadcast treatment than in the control and 50 cm treatment.
During the 9 years of the study, total aspen density decreased from approximately 50000 to 22000 stems ha-1. Tall aspen density (i.e., the density of aspen as tall or taller than the target lodgepole pine) was approximately 5000 stems ha-1 at age 9 years. At that time, tall aspen density was more strongly correlated than was aspen basal area with pine stem diameter growth. Related work (Newsome et al. 2003) showing that competition effects are only weakly expressed in 9-year-old pine-aspen stands suggests the need for longer-term measurements at the Tyee Lake site.
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Updated May 11, 2007