Identifying understory diversity and resilience patterns with the depth-to-water index in boreal mixedwood forests

• Author / Creator

  Echiverri, Laureen F. I.

• For the purpose of informing biodiversity conservation efforts in managed landscapes, we explored whether and how understory plant communities (abundance, diversity, composition) were related to a topographic moisture index, called depth-to-water, in the boreal mixedwood forests of northwestern Alberta. As a measure of resilience, we also examined if these relationships were changed by retention harvesting, 15 years after harvesting. Sample plots were placed along the depth-to-water moisture gradient in three forest types: coniferous, mixedwood, and deciduous, and in four retention harvesting treatments: unharvested (control), 50% retention, 20% retention, and clearcut (2% retention). Understory diversity, abundance, and composition were measured for each plot. In unharvested stands, we found understory attributes were related to the depth-to-water index with the relationships varying among forest types. In coniferous stands, we found higher diversity and abundance (cover) on drier sites. In deciduous and mixedwood stands, understory abundance was higher on drier sites, but diversity was not related to the depth-to-water index. Lastly, composition was significantly, but weakly, related to the depth-to-water index in all three forest types. Harvesting affected the relationships between understory variables and the depth-to-water index; again, effects differed between forest types. Coniferous stands were the least resilient forest type, as most relationships between understory attributes and the depth-to-water index in these stands were affected by harvesting. For instance, harvested coniferous stands had higher diversity on wetter sites, rather than on drier sites as was seen in the unharvested stands. Mixedwood stands were the most resilient forest type−only the relationship between composition and depth-to-water was affected by harvesting. In deciduous stands, relationships of abundance and composition with depth-to-water were changed by harvesting. The relationship between abundance and depth-to-water was weaker in harvested, as compared to unharvest, deciduous stands. Within the stands, resilience also varied along the depth-to-water gradient. Wetter sites were less resilient in coniferous and mixedwood stands, while drier sites were less resilient in deciduous stands. Our study shows that the depth-to-water index can be used to identify understory distribution and resilience; hence it can be useful for identifying areas to be targeted for conservation.

• Subjects / Keywords

  • Boreal forests
  • Moisture index
  • Depth-to-water
  • Retention harvesting
  • Plants
  • Understory vegetation
  • Harvesting

• Graduation date

  Fall 2017

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3FX74B9B

• 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.