In 1999, an experiment was established to examine the effects of reducing aspen density on stand-level lodgepole pine and aspen growth in the SBSdw1 biogeoclimatic variant of the Cariboo-Chilcotin. Aspen retention treatments of 0, 500-800, 1000-1500, and 2000-2800 stems ha-1 were applied in an 11-year-old mixed-species stand of aspen and lodgepole pine. One year after cutting, aspen basal area in these retention treatments was 0, 1.25, 3.05, and 2.89 m2 ha-1, respectively, compared with 5.36 m2 ha-1 in the control. Four years after treatment, based on stand-level measurements taken in permanent measurement plots, pine vigour tended to be better in treatments where <1000 aspen stems ha-1 had been retained but there were no significant differences in mean stand-level lodgepole pine height, stem diameter, quadratic mean diameter, or basal area as a result of the aspen retention treatments.
Aspen suckering was assessed 2 and 4 years after cutting. Sucker densities differed significantly between aspen retention treatments after 2 years, ranging from 28 187 stems ha-1 in the complete aspen removal treatment to 344 stems ha-1 in the 2000-2800 stems ha-1 treatment. Sucker densities appear to have declined naturally by approximately 35% between years 2 and 4 after cutting; however, this apparent decline may be partly due to a change in the sampling method. There were no significant differences between treatments in sucker height in either year 2 or 4 after cutting.
In addition to stand-level measurements, the ongoing performance of target lodgepole pine that had, or had not, met existing British Columbia Ministry of Forests free-growing requirements at a stand age of 12 years was assessed. By 2003, pine in the free-growing group were larger than those in the not free-growing group according to all measurement criteria. Regression analysis showed that tall aspen (i.e., aspen at least as tall as the target pine) within a 1.78-m radius were more important competitors with the target pine than aspen that were further away. When the stand was 13 years old, tall broadleaf basal area explained 25.7% of the variation in 2000-2003 lodgepole pine stem diameter increment.
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Updated May 11, 2007