Riparian restoration on Lyell Island, Haida Gwaii: understory vegetation and light

Gwaii Haanas National Park Reserve, National Marine Conservation Area Reserve and Haida Heritage Site (Gwaii Haanas) has undertaken a riparian restoration project on Lyell Island that aims to restore salmon habitat and enhance biodiversity values. Past forestry practices in Sandy Creek, Lyell Island have left a dense forest canopy and introduced deer have left a depauperate understory. A range of openness treatments were used in the riparian forest of Lyell Island, Haida Gwaii, to create a more heterogeneous forest structure and light environment in the understory. This research examines the understory vegetation community of this ecosystem, as well as the change in light environment post-treatment due to the restoration, and one-year-post due to wind events throughout the winter. We found that tall stumps left over from logging provide important refugia from deer browsing. Mean height and percent cover of vegetation was significantly greater on stumps. However, species richness and diversity were greater in all ground plots. Mean height was significantly greater within exclosures, than in open ground plots. Maintaining exclosures and continuing deer control measures will be important if managers wish to restore understory biodiversity within Gwaii Haanas. Forest structure variables (basal area, and stand density), as well as light environment variables (percent full sun, canopy openness and effective leaf area) changed significantly post-restoration due to the treatments. Percent full sun increased in similarity to the percent full sun as measured in the old growth comparison in Windy Bay. One-year-post restoration showed similar mean values in most variables but higher standard deviations for percent full sun due to wind events throughout the winter: more similar to the spread of old growth light levels. This research will help inform management techniques for future restoration project success in Gwaii Haanas.