Regeneration in thinned and unthinned uneven-aged interior Douglas-fir stands

The specific objectives of this study were to: (i) assess the impact of overstory conditions and disturbance history of interior Douglas-fir dominated stands on the quantity and quality of regeneration present; and (ii) document the impact of mountain pine beetle (Dendroctonus ponderosae Hopkins) on the regeneration in these types of stands. Overstory tree data from permanent sample plots and regeneration data from newly installed permanent subplots on each of the overstory plots were collected and compiled by plot, block, and treatment on a pre-commercial thinning experiment installation. This installation is located in drybelt Douglas-fir stands on the Knife Creek Block of the UBC Alex Fraser Research Forest in the vicinity of Williams Lake, BC. Several methods of assessing regeneration quantity (number of germinants and seedlings) and quality (three-year height growth) were used: mixed models, zero-inflated general linear models, and Classification and Regression Tree. Regeneration quantity and quality differed across the study site. Block B had relatively few seedlings and all were Douglas-fir; the other two blocks (C and D) had more regeneration comprised of several species. The control plots on all blocks had low amounts of Douglas-fir regeneration. Seedlings in the control plots had the lowest predicted three-year height growth, while the best height growth was found in the 5 m clumped spacing. Plot (larger scale) variables were less important than other variable types for determining the number of seedlings in a subplot. Having less than 35% ground coverage of crown litter (dead needles, small twigs, etc.) on a subplot was the best indicator of the presence of germinants. The best variables to predict the presence of seedlings were grass and herb ground coverage of more than 15% and less than 25% ground coverage by crown litter. The number of germinants did not vary significantly among treatments, although fewer were found on the control plots. Plots were compared to determine the effect of lodgepole pine mortality on the quantities of seedlings or germinants present. There was only weak evidence that seedling quality (as reflected by three-year height growth) was better on plots that had higher levels of recent mortality.Forestry, Faculty ofGraduat