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Stand and tree dynamics in uneven-aged interior Douglas-fir stands Nienaber, Gordon Wesley

Abstract

The Interior Douglas-fir Biogeoclimatic Zone covers 4 million hectares in the southern interior of British Columbia. This zone is dominated by interior Douglas-fir forests which are valued for their timber, wildlife, range and recreational values. Interior Douglas-fir can be found growing naturally in uneven-aged structured stands; a structure that forest managers often want to maintain for its ability to sustain multiple values. However, the growth dynamics in these stands are complex and little is known about the interactions that occur among the individual trees of varying ages and sizes. The objectives of this study are to address this lack of understanding at both the individual tree and stand levels. Data were collected at an installation of permanent sample plots established in uneven-aged stands of interior Douglas-fir at the Knife Creek Block of the Alex Fraser Research Forest, near William's Lake, B.C. These data were used to explore growth trends that may be attributed to the differences in stand structures among the plots. These data were also used to assess several competition indices representing a range of complexity in order to investigate the growth dynamics within the study stands. The competition indices were evaluated by testing non-linear regressions that used the indices and dbh to predicting dbh growth. The performance of the regressions were then compared to the performance of a base regression that used dbh alone. It was found that the growth of the various stand level attributes measured was similar among the plots despite the differences in stand structures. The assessment of the competition indices revealed that the least complicated of the individual tree level indices tended to produce the best performance. The distance dependent indices consistently performed better than the distance independent indices. From the analysis results it was inferred that a relationship of relative symmetry, also termed resource depletion, exists among the study trees. This implies that competition occurs mainly for below ground resources. The relationship between the trees was found to be two-sided due to the influence that small trees had on larger trees.

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