Presenter/s: Daphnee Tuzlak
Symposium Session: 2024 - 05 Doing More with Less for the Love of Monitoring
Topics covered: adaptive management and monitoring, canada, riparian, and traditional ecological knowledge
ABSTRACT
Salmon populations along the coast of British Columbia have precipitously declined. Industrial logging has altered freshwater and estuarine habitats, yet those implications have rarely been systematically documented either temporally or spatially especially relative to old-growth reference conditions. The purpose of this study was to analyze a long-term historical air photo record (1937-2019) in hiłsyaqƛis (Tranquil) River watershed, ƛaʔuukʷiʔatḥ (Tla-o-qui-aht) Nation Territory, Clayoquot Sound, to identify and map the changes in structural habitat conditions for Pacific salmon spatially and temporally, both instream and in the riparian zone. Logging patterns in Tranquil Creek are very typical for coastal BC. Industrial logging occurred without any regulations in Tranquil Creek in the 1950s-1960s when the riparian zone and valley bottom were completely clear cut. The hillslopes were logged in the 1980s and 1990s again with little regulations, including for roads. Chinook salmon populations are now only 3% of their historical abundance so of special concern. Using a series of historical orthophotos, we mapped changes in stream and riparian conditions in Tranquil Creek over 82 years. The rate and scale of channel changes varied between reaches and were associated with the retention of an old-growth riparian forest or buffer, bank erodibility, floodplain elevation, and whether the channel is alluvial, semi-controlled, or bedrock. These channel changes were most profound in the lower alluvial reaches, which were originally alluvial Sitka spruce forest and prime Chinook habitat. In one location, the bankfull channel width increased by over four times: 60 m in 1937 to 250 m in 2019. From 1970 to 2019 there has been a 41% decrease in large wood area and decreases in pools in some reaches and pools being infilled in bedrock-constrained reaches. The results of the study highlight the importance of evaluating changes in the function of the riparian zone, especially relative to reference old-growth habitat conditions that salmon have presumably evolved. These reference conditions may be especially important in an era of climate change. Additionally, we present our recommendations for process-based restoration and policy defining riparian systems and buffers.