Mortality and Growth of Residual Whitebark Pine in High Elevation Variable Retention Harvest Sites in Southeastern British Columbia




Berg, Jenny

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The rapid decline of whitebark pine (Pinus albicaulis) throughout its range is a pressing conservation issue. This keystone species endures multiple pressures toward local extirpation including forest health agents, forest succession, and climate change. Currently, silviculture practices are categorized as a stand-level strategy aimed at effective whitebark pine restoration/conservation. In this thesis I retrospectively evaluated the mortality and growth of whitebark pine at five low-retention ESSF silviculture treatments located in southeastern British Columbia, Canada. I found that whitebark pine reserve trees in low retention silviculture prescriptions were prone to elevated post-harvest mortality due to windthrow within the initial five-year post-harvest interval. Post-harvest growth rates indicated that mature reserve trees were likely to demonstrate increased radial growth after disturbance and that pre-harvest growth rates due to suspected forest health agents can minimize these increases. A two sample Welch t-test found no significant difference between the resistance index of control and reserve trees one year after harvest in three of the four sites examined, suggesting that radial growth reduction was negligible for surviving trees. Visual examination of the post-harvest reserve tree chronologies, however, showed a common two to three-year growth lag. Reserve trees indicated a significant difference in the recovery period for the harvest event year with a one-year lag in two of the four sites. However, this result was confounded by the following: (1) one of the sites showed a negative radial growth trend pre-harvest; and, (2) a pointer year analysis identified an inflated growth response in the control trees for the same year for the second site. These growth-climate relationships indicated that whitebark pine tree chronologies in closed-canopy forests were energy-limited systems with a significant negative correlation to July SPEI.



Variable Retention, Whitebark Pine, Dendrochronology