Influence of variable retention and deadwood characteristics on saproxylic beetles in boreal white spruce stands

• Author / Creator

  Lee, Seung-Il

• Retention forestry aims to maintain a significant level of continuity in forest structure, composition and complexity so as to support conservation and recovery of biodiversity and ecological function on managed landscapes; however, the amount and distribution of retention that best meets conservation goals remains unclear. The problem of biodiversity loss through direct effects of forestry seems most demonstrably acute for the saproxylic biota (i.e., species associated with deadwood). In this dissertation, I sought to understand how deadwood characteristics and variable retention harvest influence the composition and diversity of saproxylic beetle assemblages in boreal white spruce (Picea glauca) stands on the western boreal plain of Canada. I worked in both the EMEND (Ecosystem Management Emulating Natural Disturbance) experiment and in nearby industrial harvest blocks, located in northwestern Alberta, Canada. My general thesis is that forest management can be adjusted to be more sensitive to saproxylic biodiversity, and particularly, that mixing dispersed and aggregated retention on cut-blocks leads to better outcomes than traditional clear-cutting. Overall, 75 719 saproxylic beetles representing 377 species in 44 families were collected using window traps, emergence traps and rearing drums. Most were identified to species and these records constitute the database for this dissertation. I have demonstrated that saproxylic beetle assemblage structure changes progressively over the decompositional stages of white spruce deadwood, emphasizing that retention of the entire range of decay classes is necessary to conserve the associated saproxylic beetle fauna on post-harvest landscapes. Beetle assemblages also responded to retention patch size and to different levels of dispersed retention surrounding retention patches. Although small retention patches maintained or attracted representative populations of ‘initial colonizers’ 10 years post-harvest, beetle assemblages in patches ≤ 2.93 ha were strongly influenced by edge effects and less similar to those in intact forests than in larger patches. I also showed that relatively small retention patches (0.20 ha and 0.46 ha) surrounded by higher levels of dispersed retention (i.e., 20% and 50%) provided conditions sufficient to retain assemblages of early colonizing species that are broadly similar to those in intact forests. Thus, my work underscores that using a combination of aggregated and dispersed retention on harvested blocks will better conserve saproxylic beetle species than leaving patches alone. This dissertation contributes to a more complete understanding of how retaining living green trees at harvest can be strategically adjusted to achieve better results for saproxylic beetles, a bio-diverse functional group that has been negatively affected by traditional forestry.

• Subjects / Keywords

  • Edge effects
  • Saproxylic beetles
  • White spruce
  • Coarse woody debris
  • Retention forestry
  • Forest management
  • Dispersed retention
  • Aggregated retention

• Graduation date

  Spring 2016

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3WS8HX44

• 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.