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


Other title
retention harvesting
moisture index
understory vegetation
boreal forests
Type of item
Degree grantor
University of Alberta
Author or creator
Echiverri, Laureen F. I.
Supervisor and department
Macdonald, Ellen (Renewable Resources)
Examining committee member and department
Nielsen, Scott (Renewable Resources)
Stadt, John (Government of Alberta)
Carlyle, Cameron (Agricultural, Food and Natural Sciences)
Department of Renewable Resources
Forest Biology and Management
Date accepted
Graduation date
2017-11:Fall 2017
Master of Science
Degree level
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.
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