Mountain pine beetle and forest harvest effects on hydrologic processes and streamflow in the Alberta Foothills

  • Author / Creator
    Goodbrand, Amy R
  • The Alberta Foothills region has experienced an unprecedented mountain pine beetle (MPB) outbreak. The provincial management strategy is to contain the infestation with forest harvest. The landscape becomes a patchwork of dead (MPB grey-attack), alive, and harvested stands. MPB attack affects the water transport in trees and results in the gradual loss of the canopy structure, which has the potential to affect hydrologic processes. Therefore, there is a need to understand MPB and forest harvest effects on runoff generation and the streamflow response, especially in watersheds that provide habitat for the endangered Athabasca Rainbow Trout (ARTR). Research questions addressed in this thesis were: 1) what is the effect of varied canopy cover loss on stand water cycling in the Foothills; 2) what is the effect of forest harvest on streamflow in a Foothills watershed; and, 3) what is the effect of potential streamflow changes from MPB grey-attack and forest harvest scenarios on ARTR fry recruitment in a Foothills stream? Methods included a combination of statistical and hydrological modelling as well as data from the MPB Ecohydrology stand-level study and a long-term dataset from the Tri-Creeks Experimental Watershed (Tri-Creeks) near Robb, Alberta. Tri-Creeks has complex glacial deposits underlain by sedimentary bedrock; a geological setting with large potential for subsurface water storage. In addition, climate variability, especially meteorologically driven changes from the Pacific Decadal Oscillation (PDO), influence streamflow. Results from stand-level water balance models showed root zone drainage from the MPB grey-attack stands were similar to an undisturbed mature lodgepole pine stand. Compensatory increases in evapotranspiration from surviving vegetation (unaffected trees or understory vegetation) were predicted in the grey-attacked stands. The greatest root zone drainage occurred in the harvested stand. Results indicate regional differences in hydrologic processes that generate runoff in MPB and harvested stands. Historical clear-cut harvest within Tri-Creeks sub-watersheds was predicted to result in a significant measurable increase in rainfall-generated peak runoff events and summer runoff. However, increased runoff from harvested watersheds may have been attenuated by the drier antecedent watershed conditions in the warm PDO phase. Climate variability, in relation to antecedent watershed storage, remained a strong control on runoff generation in the watersheds. Watershed disturbance scenarios showed MPB grey-attack produced no effect on simulated streamflow response, while simulated clear-cut harvest (52% watershed area) resulted in 15% greater mean annual water yield than if grey-attack trees were left standing. Increased streamflow from forest harvest above the critical discharge threshold for streambed movement of ARTR spawning substrate during the incubation period was predicted to reduce fry recruitment, but annual fry recruitment was estimated to occur over the 50-year simulated streamflow record. Reduced fry recruitment from forest harvest was not likely to produce measurable change at the population level. Overall, results from this thesis provide better understanding of the MPB and forest harvest effects on hydrologic processes and streamflow in the Alberta Foothills and could factor into decisions about MPB strategies with respect to the endangered Athabasca Rainbow Trout.

  • Subjects / Keywords
  • Graduation date
    Spring 2021
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.