Assessment of Post-Disturbance Regeneration in the Ubc Alex Fraser Research Forest’S (Afrf’S) Knife Creek Block
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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 by Emmanuel Adoasi-Ahyiah B.Sc., Kwame Nkrumah University of Science and Technology, 2017 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES (Forestry) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) September 2020 © Emmanuel Adoasi-Ahyiah, 2020 The following individuals certify that they have read, and recommend to the Faculty of Graduate and Postdoctoral Studies for acceptance, the thesis entitled: 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 submitted by Emmanuel Adoasi-Ahyiah in partial fulfillment of the requirements for the degree of Master of Science In Forestry Examining Committee: Dr. Verena C. Griess, Associate Professor, Department of Forest Resources Management, UBC Supervisor Dr. Adam Polinko, Post-doctoral Fellow, Department of Forest Resources Management, UBC Supervisory Committee Member Dr. Allan Carroll, Professor, Department of Forest and Conservation Sciences, UBC Supervisory Committee Member Dr. Lori Daniels, Professor, Department of Forest and Conservation Sciences, UBC Additional Examiner i Abstract 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. ii Lay summary Forest management in the central interior landscapes of British Columbia is challenged with conflicting timber production and mule deer winter range (MDWR) maintenance management goals. This is further exacerbated by the issues of disturbances (e.g. wildfires, bark beetle, defoliators and harvesting), and species succession following these disturbances. Interior Douglas- fir is instrumental in providing timber for harvest, and for mule deer habitat maintenance. Given its importance, the regeneration of interior Douglas-fir was assessed together with growing space variables that influence species establishment and growth in greater than 0.1ha gaps. The findings of the study indicated that natural regeneration was not sufficient to meet MDWR requirements without external management intervention. Growing space availability had a weak relationship with regeneration and growth. However, its potential impact is important and management prescriptions must assess and include the influence of growing space variables in seedling establishment and growth. iii Preface This thesis was made possible with the collaboration of my supervisory committee members, Drs. Verena C. Griess, Adam Polinko and Allan Carroll, who provided me with utmost support and guidance in the development and execution of my research questions and objectives, research methodology, and provided detailed edits and comments in all chapters of the thesis write-up. Dr. Adam Polinko provided guidance in conducting data analysis for Chapter 3. Further, the Alex Fraser Research Forest provided some equipment and support during the data collection period for the research field work. Finally, I was responsible for developing the research questions and objectives, research methodology and sampling design, data collection and data analysis for chapter 3 coupled with the full write-up of the thesis. Chapter 3 is expected to be submitted for scientific publication. iv Table of contents Abstract ........................................................................................................................................... ii Lay summary ................................................................................................................................. iii Preface............................................................................................................................................ iv Table of contents ............................................................................................................................. v List of tables .................................................................................................................................. vii List of figures ............................................................................................................................... viii List of abbreviations ...................................................................................................................... ix Acknowledgements ......................................................................................................................... x Dedication ..................................................................................................................................... xii Chapter 1: Introduction ................................................................................................................... 1 1.1 Background ........................................................................................................................... 1 1.2 Thesis statement .................................................................................................................... 4 1.3 Thesis objective and implication for Knife Creek ................................................................ 4 1.4 Thesis structure ..................................................................................................................... 5 Chapter 2: Literature Review .......................................................................................................... 6 2.1 Physiological response of interior Douglas-fir...................................................................... 6 2.2 The dry interior Douglas-fir forest of British Columbia ....................................................... 8 2.3 Biotic and abiotic disturbances in the dry interior Douglas-fir forest ................................. 10 2.4 Fire disturbance in interior Douglas-fir forests ................................................................... 12 2.5 Douglas-fir beetle disturbance in interior Douglas-fir forests ............................................ 13 2.6 Natural regeneration and growing space dynamics in interior Douglas-fir forests............. 15 2.7 Management of interior Douglas-fir forests ........................................................................ 18 Chapter 3: Douglas-fir natural regeneration dynamics in the Knife Creek block of the UBC AFRF post-disturbance ............................................................................................................................ 22 v 3.1 Introduction ......................................................................................................................... 22 3.2 Research objectives and questions ...................................................................................... 26 3.3 Hypotheses and predictions ................................................................................................. 27 3.4 Methodology ....................................................................................................................... 27 3.4.1 Study area ....................................................................................................................