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UBC Theses and Dissertations

Effects of pre-commercial thinning on the dynamics of uneven-aged interior Douglas-fir (Pseudotsuga menziesii var. glauca) stands in British Columbia, Canada Acquah, Stella Britwum


This dissertation sought to gain insight into the impacts of pre-commercial thinning (PCT) treatments on the development of uneven-aged interior Douglas-fir (IDF) stands in central British Columbia, Canada. Data were available from 24 plots in 3 blocks of a long-term study on the response to PCT, comprised of 5 measurements over 21 years. Growth responses at the stand level and for trees of 3 conifer species (interior Douglas-fir - FD; interior spruce - SX; and lodgepole pine - PL) were assessed. The PCT enhanced the growth rate of the residual trees at the stand and individual tree levels. I compared the performance of 13 competition indices (5 non-spatial and 8 spatially-explicit) to predict individual tree periodic annual basal area increment (PABAI) of the three species and investigated whether neighbouring trees competed with subject trees independently of species identity. Also, I examined the differences in individual tree basal area growth among the three species over time under different levels of competition. The spatially-explicit competition indices were more effective in predicting PABAI than their non-spatial counterparts for all species. Asymmetrical relationships between these species and their neighbours were observed, indicating that aboveground competition for light was the main factor limiting growth. FD had higher PABAI than SX and PL, irrespective of the competition intensity. The Gini coefficient (GC) and the growth dominance coefficient (GDc) were applied to the thinned and unthinned plots to determine how size inequality and growth dominance changed over time. Size inequality was reduced following thinning. GDc decreased with increasing thinning intensity, suggesting that smaller trees were proportionately more vigorous as the thinning intensity increased. Temporal changes in tree spatial patterns were assessed using spatial point pattern analysis. The thinning treatments influenced the spatial pattern of trees with a trend away from clumpy distributions and towards random or regular spatial patterns, while the unthinned plots remained clustered through time. This study provides new insights into the stand dynamics of the uneven-aged IDF stands as observed over a 23-year period, particularly as it relates to different applications of PCT.

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