Composition and structure of spider assemblages in layers of the mixedwood boreal forest after variable retention harvest

  • Author / Creator
    Pinzon, Jaime
  • Natural disturbances are important drivers of ecosystem change in the boreal forest and new approaches to sustainable forest management draw on natural disturbance patterns as a template for harvesting. The main premise for such approach is that species have evolved and adapted to stand-replacing natural disturbances and thus are more likely to be maintained on landscapes managed so as to preserve spatial patterns of natural disturbance. I used spiders – one of the most important, diverse and ubiquitous groups of terrestrial predatory invertebrates – as a model for assessing the impacts of variable retention harvesting practices on biodiversity in the mixedwood boreal forest. Spiders were collected from the Ecosystem Management Emulating Natural Disturbance (EMEND) project landbase over a period of five years (five to nine years post-disturbance) from different harvest treatments and forest habitats. Results from this study show that changes in composition of spider assemblages clearly followed the variable retention disturbance gradient (clear-cut to uncut treatments) and these changes were linked to habitat and forest structure. In general, low tree retention (i.e., 10-20% which is the range currently applied by the forestry industry) showed some ability to mitigate adverse effects of clear-cutting; yet, higher retention levels are needed to maintain forest specialist species, especially in late successional seres (e.g., conifer dominated). A “life-boating” effect of aggregated retention was also evident, and it was more effective when applied in combination with dispersed retention. The application of different harvesting practices alone is unlikely to entirely emulate some of the effects and processes caused by major disturbances on the landscape. Thus, keeping in mind that fire is an important and vital component in the boreal forest, this type of disturbance cannot be excluded from management if the goal is to preserve a natural range of biodiversity. In conclusion, to sustain rich and diverse spider assemblages, management of the boreal mixedwood should aim towards maintaining landscape heterogeneity. Consequently, no single harvesting practice is effective to emulate natural post-disturbance patterns and to adapt harvesting to effectively imitate the processes of a disturbance driven system, a combination of prescriptions is recommended.

  • Subjects / Keywords
  • Graduation date
    Fall 2011
  • 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.