The fish living in the rivers of the Pacific Northwest generally don’t like the sun beating down on them. They are cold-loving species. This is particularly true for salmonids at crucial stages in their life cycle. The rivers in which they roam and reside can be surrounded by forests, owned both publicly and privately. When the riparian canopy around these forests are preserved, the solar load of the sun decreases. More shade means the preservation of lower water temperatures. Yet, how much canopy is enough for different life stages? How much logging can be allowed in the riparian zone of a river in different parts of Oregon? How far downstream does a stream “remember” a heat signal? Besides shade, what other stream characteristics help or hinder temperature for salmonids?
I worked with the Oregon Stream Protection Coalition (OSPC) to help them advocate for better answers to these questions from the Oregon Board of Forestry (OBF) as the OBF deliberated the Rule Making for the Cold Water Criterion. The OSPC believes the buffer widths and compositions are inadequate to protect stream temperatures. In my work, I reviewed prior petitions and reports of the OSPC, analysis by OBF scientists, and relevant scientific and management literature. I delivered a 5-page, 13-figure report, with the following arguments as a few highlights:
While the OBF has commissioned a cost analysis to forestry from decreased harvest volumes, they need to commission a benefits analysis to fisheries from increased fish health and habitat. The valuation of an important ecosystem service would provide a comprehensive and balanced cost-benefit analysis for stakeholders to consider.
In the RipStream studies, private forestry land forestry operations were shown to have greater impacts to stream temperature than State forestry operations (Groom et al. 2017). The OBF ought to adopt a more risk-averse approach in the assumptions and methods provided by the RipStream Bayesian Model (Groom et al. 2018). Additional scenarios ought to be run through the model, and the RipStream Model ought to be compared to other tools (as mentioned below).
The heat memory of downstream from a harvest reach is longer than currently recognized by the OBF. This is due to a simplistic view of how stream temperatures work, where the singular mechanism of shading is king. Riparian shading is important, yet other mechanisms such as hyporheic flux, groundwater accretion, and tributary flows are important too. Along the run of a river from headwaters to mouth, they each create discontinuities of temperature fluxes. The locations and temperature changes of these discontinuities change the ability of rivers to recover from impacts (i.e. assimilative capacity). Additional tools (e.g. DEQ and SSN) can address the more complex system dynamics, and ought to be tested by the OBF across the rivers of the RipStream studies. The figure 1 below conceptualizes these issues.
My report is slated to go into a petition by the OSPC to the OBF. Hopefully, it will lead to better insight to stream temperature dynamics, a more balanced perspective to managing stream temperatures, and larger riparian buffers on small and medium streams in Oregon.
Figure 1: Framework comparing the locations and processes (single v. multiple) relevant to using analytical tools to address both localized (single site) and longitudinal (multiple sites) changes in temperature and assimilative capacity along rivers.