UBC Theses and Dissertations
Soil development and forest productivity on naturally regenerating landslides on Vancouver Island Straker, Justin
A chronosequence of five naturally regenerating landslide tracks on the west coast of Vancouver Island was studied, to identify processes of soil and vegetation recovery that might be adapted for use in slide rehabilitation programs. Information on soil physical and chemical properties (forest floor depth, coarse fragment content, texture, bulk density, pH, organic matter content, total N, extractable P, exchangeable K, Ca, and Mg) was collected on slide scour and deposit zones, and on equivalent slope positions on adjacent stable ground. Data on current stand attributes (stocking, height growth, and volume production) were collected in order to estimate the effects of landsliding on forest productivity. Two younger rehabilitated slide scars were included for study, to provide comparison between natural regeneration processes and those initiated by rehabilitation actions. Sixteen additional natural and rehabilitated landslides were included to extend the geographic range of the forest productivity component of the study. Sites ranged in age from 6 months to 100+ years since failure, and in current state from unvegetated to supporting mature conifer stands. Alteration of analyzed soil properties occurred rapidly as slide tracks revegetated. Although general trends follow those observed in other chronosequence work, the extent and rate of changes recorded in this study are attributed to red alder dominance of early successional phases on slide tracks. Although alder was a major component of regeneration on all slides studied, in all cases stand development followed predictable successional patterns towards eventual conversion to conifer species. Observed trends in soil properties stabilized or reversed under conifer dominance. Results of timber cruising indicate consistency in both alder and conifer volume production as slide scars age, with 20-year age classes being reliable predictors of stand volume. Reductions in conifer volumes on landslide tracks greater than 60 years of age were 50-60%, as compared to adjacent old-growth stands or projected second-growth stands. Based on findings from this research, a number of potential avenues for slide rehabilitation work are discussed. Particular emphasis is placed on management options for retaining alder as a component of regeneration, and to selection of conifer species for inclusion in slide planting programs.
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