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UBC Theses and Dissertations

Natural regeneration dynamics of interior Douglas-fir : assessment of post-disturbance regeneration in the UBC Alex Fraser Research Forest’s (AFRF’S) Knife Creek block Adoasi-Ahyiah, Emmanuel


Licensees are required to regenerate interior Douglas-fir (Pseudotsuga menzisii var glauca) forest gaps greater than 0.1ha to meet and maintain species distribution across age classes for stands, biodiversity (such as mule deer winter range (MDWR)), and recreational objectives. However, little is known about the dynamics of natural regeneration in these forests. To understand future stand structure and composition, I investigated the regeneration dynamics and growth of interior Douglas-fir post-disturbance, and the influence of growing space availability on the dynamics of interior Douglas-fir regeneration and growth. I identified 181 gaps greater than 0.1 ha in the Knife Creek block of the UBC-Alex Fraser Research Forest. Sanitation harvests to control Douglas-fir beetle (Dendroctonus pseudotsugae) created salvage gaps, while biotic disturbances (e.g. windthrow) created natural gaps. Regeneration density and growth attributes of interior Douglas-fir were assessed in 600 1,000thha randomly laid circular plots across identified gaps. Growing space variables, such as slope, leaf area index (LAI), topographic wetness index (TWI), elevation, and aspect were obtained using hemispherical photographs and digital elevation models for each plot. Additionally, the distance of each plot to the gap edge, ground cover, site series and site index growing space variables were determined. Based on the findings of the study, I do not accept the hypothesis that the establishment and growth of interior Douglas-fir will increase with increasing available growing space in the gaps of regenerating Douglas-fir stands, and that growing space availability will have an influence on the establishment and growth of naturally regenerating seedlings. . However, only light (LAI) was directly measured using hemispherical photographs whereas moisture (TWI) was modelled from DEM data that may not have reflected microsite conditions. The findings of the study revealed that approximately 70% of the gaps did not meet stocking requirements, out of which about 40% had no regeneration. Additional research is needed to fully understand the dynamics of interior Douglas-fir regeneration and growth in these gaps over temporal and spatial scales. This will enable management to make more informed decisions on post-disturbance silvicultural prescriptions within the Alex Fraser Research Forest.

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