Why are source streams important?
Small streams are sensitive to their local, reach-scale surroundings and disturbance to the forest nearby. This sensitivity starts as a dramatic response to changes in light caused by canopy removal (i.e., forest harvest). This in turn results in rapid heating (and in winter, cooling) of the small volume of water, with impacts on biogeochemical rates and biological diversity. Changes in local hydrology resulting from increased peak flows following harvesting (reduced evapotranspiration, compacted soils, drainage from roads, etc.) can result in higher rates of erosion and sediment transport, changes in geomorphology, and transport of higher nutrient loads. Removing surrounding vegetation alters stream food webs by increasing primary production and reducing inputs of organic matter, and even as vegetation regrows, the type of vegetation remains different from the original composition, which affects stream food webs. Finally, a small catchment area means small streams are vulnerable to low flows during dry periods and temporary drought, which is exacerbated by nearby harvesting.
It is increasingly apparent that lack of protection from source streams to downstream has resulted in degradation of stream and river networks, reduced their productivity, and incurred enormous expenses to restore (rarely successfully) downstream areas. The dependence of downstream reaches on upstream source areas has been demonstrated because source streams supply water, nutrients and organic matter to downstream, hydrologically connected systems. Source streams also support unique and high biodiversity ecosystems providing critical habitats to many species, and are among the most vulnerable of freshwater ecosystems.
No-one has addressed the trade-offs between protection of source areas in terms of costs to the forest industry and society at large, the values of the ecosystem services provided or the mitigation of uncertainty associated with climate change and other environmental changes. We have developed a three-part approach to address this challenge:
1. Field-based experiments – We will conduct field studies to investigate the ecological, chemical and biological conditions of different streams with different levels and ages of management interventions. These experiments will be controlled flow-through stream mesocosm studies and will provide additional information about the mechanisms by which reach-scale disturbance from forestry activities affects source streams. Field work will take place across the three regions (Canada, Finland and Sweden). Our results will contribute to the existing knowledge of ecological responses to riparian management and will also serve as a testing data set for the outcomes of the models described below.
2. Network Modeling – We will develop catchment-scale models to evaluate the contributions of different forestry practices around source streams to local and downstream ecosystem integrity and to compromises of ecosystem services. These process-based models will integrate what we know about the magnitudes and durations of impacts from forest harvesting on a number of response measures, and consider the additive and interactive effects among the driving variables. The response measures will be the impact on local and downstream systems and effect sizes of deviations from reference ecological status. The models will include comparisons of changes in supplies of timber and water resources, using scenarios based on different landscape designs, particularly on the allocation of riparian forest protection around different features of catchments (e.g. source streams versus larger streams, buffer widths, continuity of buffers, etc.).
3. Stakeholder dissemination – We will develop a white paper on riparian area management to provide guidance on how to design riparian area protection at multiple scales (reach and catchment scales). Additionally, we will also incorporate ecosystem services as incentives to sustaining proper functioning condition of stream networks. A white paper will be developed to provide a detailed design for a future, distributed experiment to test the effectiveness of reassigning allocations of riparian protection for stream networks.