Forest Investment Account (FIA) - Forest Science Program
FIA Project Y091046

    Stream habitat and bull trout (Salvelinus confluentus) responses to MPB riparian salvage harvesting in north-central British Columbia
Project lead: Hinch, Scott (University of British Columbia)
Contributing Authors: Hinch, Scott G.; Mellina, Eric
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
Riparian zones help maintain the integrity of small stream ecosystems by providing shade, large organic debris, cover for stream-dwelling fish, and energy in the form of allochthonous organic matter, as well as stabilizing streambanks and intercepting sediments. Because logging practices that remove streamside timber have the potential to alter a streams physical and biological characteristics, protective measures such as the Forest and Range Practices Act were enacted in British Columbia to help maintain riparian functions around fish-bearing streams, most commonly through the retention of buffer strips. Although there exists a relatively large body of literature on the post-harvesting effects of streamside logging practices, the vast majority of fish-forestry research has been conducted in coastal areas (this despite the fact that much of the timber supply in the immediate future will be from interior boreal & sub-boreal forests). Furthermore, most fish-forestry studies encompass a relatively short post-harvesting timeline (< ~ 10-15 years), leading to an additional dearth of longer-term data on stream ecosystem responses to the removal of riparian timber. Our scientific knowledge is therefore heavily biased towards short and medium-term post-logging responses in coastal systems, with little information on interior streams and on longer-term effects. This information is sorely needed given the large-scale salvage operations currently being undertaken in response to the mountain pine beetle (MPB) epidemic throughout BCs interior regions.

The distribution of bull trout (Salvelinus confluentus, a blue-listed species in BC) and the current & projected spread of the MPB in north-central BC show considerable overlap. Furthermore, there is an acknowledged dearth of information regarding the responses of stream-dwelling bull trout and their fluvial habitats to the kind of harvesting practices that can be expected under the threat of MPB salvage-logging. Our proposal seeks to bridge this knowledge gap by using a comparative survey experimental design comprising forested streams (controls) and watersheds that are currently affected by MPB to assess the shorter-term effects of salvage-harvesting on streams and their bull trout populations. In addition, because the Prince George region has undergone extensive logging in the past 30 years (with much of the logging around streams having been conducted without buffer strips), we will use watersheds that have historically been affected by insect outbreaks to assess the projected longer-term impacts of the kind of large-scale salvage logging operations currently underway in north-central BC. Such a comparative survey approach has been used successfully by the team members to assess rainbow trout physiological stress responses to logging in a previous FRBC-funded project (see Mellina et al. 2005a in team member CV), and it can act as a springboard from which to launch future logging-related research on this species (e.g., to implement a case-study experiment involving pre-and post-logging data).

Recent work conducted in north-central BC by the team members (FIA project Y051038) suggested that short and medium-term effects of clear-cut logging on small lake-headed streams and their rainbow trout populations were relatively modest despite the removal of all large-diameter trees within the riparian zones. However, the effects of streamside clear-cut logging on bull trout in this region are poorly understood. Bull trout have a different life-history and thermal requirements from rainbow trout (e.g., the former are cold-water (<12 C) adapted and are fall spawners, whereas the latter are more tolerant of warmer temperatures (15-17 C) and are spring spawners). These differences can be crucial in determining how individual fish (and ultimately populations) respond to clear-cut logging. For example, stream temperatures in small headwater streams in north-central BC are typically cold and well-suited for bull trout, and increases in stream temperature following logging would likely be detrimental for such a species but beneficial for rainbow trout. Therefore, because bull trout are a more temperature-sensitive species when compared to rainbow trout, they are more likely to be negatively affected by streamside logging practices. Post-logging temperature increases can also accelerate egg development and result in earlier emergence of fry from stream gravels. This can be beneficial for spring-spawning species like rainbow trout because it would provide additional time within which to grow and accumulate energy reserves before the onset of winter conditions (typically the season in which the greatest mortality is observed in stream-dwelling fish). By contrast, such a scenario may be detrimental for fall spawners like bull trout because fry would emerge from stream gravels earlier during the winter months, encountering unsuitable and potentially lethal conditions.

Our proposed research will address the following questions:
1) Are there differences in summertime stream temperatures between the MPB-affected & logged streams (collectively referred to as the treatment streams) and the forested control streams? How do temperatures in the treatment streams compare with the optimal and lethal temperatures for bull trout?

2) Do bull trout densities, standing crop biomass, distribution & condition differ between treatment & forested streams?

3) Do stream habitat features differ between the treatment & forested streams, and do any such differences translate into changes in bull trout abundance, biomass, and condition?

4) Do post-logging responses differ between bull trout & rainbow trout? This will be assessed by comparing the results of the current proposal with those of recent FIA-funded work conducted in north-central BC by the same team members and which suggested that interannual changes in stream habitat and rainbow trout responses were related more to environmental fluctuations and to natural differences in the study streams than to streamside logging.

Our proposal is one of the only ones we know of that addresses these issues in BCs north-central interior region, and we anticipate that the results of this project will lead to scientifically defensible best-management recommendations designed to minimize the detrimental impacts of MPB-related logging practices on small streams and their bull trout populations. Our experience and knowledge of interior stream ecosystem functioning provides us with a unique opportunity to carry out this research, and the 1-year timetable will provide results that can be used directly and immediately.

This is primarily a management-oriented research project employing real-world harvesting treatments in an area that is expected to provide the majority of BCs timber supply for the foreseeable future. As a result, the primary beneficiaries of this study are expected to be industry & government policy makers and resource practitioners (fisheries managers & foresters alike) who will be able to use the results to make scientifically defensible management decisions. Based on the results from our previous research, our industry partners have already begun considering ways to adapt their management practices, & we anticipate that within the next 1-3 years the results from this study will lead to improved resource management planning, reduced operating costs, and a greater understanding of the responses of stream ecosystems to forest harvesting practices. We will also cooperate with our research partners (UBC, MoF, MoE, DFO), who are carrying out similar research in headwater streams, in integrating & disseminating our results to maximize the lessons that can be learned from our study systems and to most effectively reach our target audiences


Final report (0.2Mb)

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Updated August 16, 2010 

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