The Impacts of Clearcutting on Understory Plants and Culturally Significant Species In Coastal Western Hemlock Forests of Vancouver Island

• Main Author: Lambert, Emily
• Other Authors: Goldblum, David, McDermid, Greg, Bender, Darren, Rogers, Sean
• Format: Master Thesis
• Language: English
• Published: Graduate Studies 2024
• Subjects: ethnobotany; forest science; chronosequence; succession; plant ecology; understory; forestry; biogeoclimatic; old-growth; Education > Sciences; Literature > Canadian (English); Physical Geography; Geography; Ecology; Forestry and Wildlife; Native American Studies; First Nations
• Online Access: https://hdl.handle.net/1880/118107; https://doi.org/10.11575/PRISM/42951

The goal of the study is to understand successional changes in an understory plant community after clear-cut timber harvesting. The forest ecosystem is within the Southern Very Wet Hypermaritime biogeoclimatic subzone in the broader Coastal Western Hemlock zone along the west coast of Vancouver Island. The ecosystem is located in Huu-ay-aht First Nations traditional territory, and the subzone falls within various Nuu-chah-nulth First Nations traditional territories. A chronosequence was used to categorize various stages of forest growth in five successional stages: Regeneration, Immature, Thinning, Mature, and Old-growth. Forests censused ranged in age from 1 to 354 years old with old-growth stages described as stands over 250 years. The leaf cover and stem density of understory plant species were recorded within 83 subplots. These metrics were evaluated with regard to environmental variables (slope aspect, elevation, canopy openness, soil pH, A horizon depth, soil profile depth, tree basal area, tree stem density, ground moss cover, and bare ground cover) to determine which, if any, factors influenced understory species composition and structure. Out of 45 species identified, 19 are culturally significant plant species to the Nuu-chah-nulth First Nations. The species restricted to one successional stage were identified, with emphasis on opportunistic species in early stages and rare species in the Old-growth stage. There was a large decrease in many culturally significant species immediately after clearcutting. There was a large decrease in species (stem density, leaf cover, species richness, species diversity) from the Regeneration stage to the Thinning stage (1 to 80 years); however, these values steadily increased thereafter. Plant leaf cover and stem density were influenced by the amount of light reaching the understory. The natural disturbance regime that shade-tolerant plants are adapted to in these old-growth forests is small-scale gap formations, which clearcutting does not mimic. Timber harvesting ...