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The structure and regeneration pattern of old-growth stands in the Moist Cold Engelmann Spruce - Subalpine Fir subzone of Central British Columbia

University of British Columbia

The need for sound management practices of high-elevation forests is becoming more and more important in British Columbia; however, there is a lack of information on the dynamics and regeneration pattern of these forests. This pilot study investigates stand dynamics by describing the structure of oldgrowth stands, and correlating the occurrence of regeneration with site factors. Three study stands, which originated after fire and appeared to be in advanced stages of succession were selected in the Moist Cold Engelmann Spruce - Subalpine Fir subzone, near Smithers, B.C. All three stands showed the same general stand structure, although the sites were slightly different. The number of seedlings, saplings, alive and standing dead trees of Engelmann spruce (Picea engelmannii Parry ex. Engelm.) was consistently very low, and, hence, excluded from the analysis. The diameter frequency distributions of subalpine fir (Abies lasiocarpa (Hook.) Nutt.) approximated a balanced distribution, but did not fit with the negative exponential function. The height frequency distributions of fir indicated the presence of at least two canopy strata. The age of the trees at breast height (1.3 m) ranged from 100 to 400 years. The age distributions did not conform to distributions expected in the old-growth stage. The age distribution of saplings indicated that in the past 100 years the number of established saplings has declined. The spatial pattern of firs changed from highly aggregated, to random, to regular, with increasing size (diameter or height). The spatial pattern of the oldest trees was aggregated possibly indicating remnants of the colonizing cohort. Since the diameter distributions and the spatial pattern of trees with different sizes are similar to that of a steady state they are not expected to change in the future. Canopy stratification was most pronounced in the oldest study stand, therefore, it is possible the height distribution will never show the inverse-J shape typically expected in old-growth forests. Due to weak size-age relationships the future change in age distribution is difficult to predict. The fir regeneration showed strong correlations with the presence of decaying wood substrate. There were more than twice as many seedlings on decaying wood than expected from the total cover of the substrate. However, survivorship from seedling to sapling stage was better on the forest floor than on decaying wood. Vegetation cover, light, and humus form showed no correlations with the number and vigour of seedlings. The occurrence of seedlings was also independent of canopy openings. This result implies that gap dynamics was not the driving force for the establishment of fir regeneration. One possible explanation is that snow melts later in canopy openings. The number of seedlings was higher than expected in the intermediate snow melt time zones which roughly corresponds to canopy edge positions. The future of the spruce component in the study stand was difficult to predict because of the very low number of individuals. The dominant position of spruce trees and presence of recently established seedlings throughout the stands would imply that there was an adequate seed source. However, without knowledge about survival of seedlings until they reach the canopy it is impossible to say whether the amount of regeneration is adequate for maintaining the spruce population.

Thesis/Dissertation

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2009-03-09

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http://hdl.handle.net/2429/5796

Forest Sciences

University of British Columbia

UBCV

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