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SALMON WATERSHEDS LAB
Ecology & Conservation of Aquatic Systems
Jonathan Moore and Team
The impacts of forestry on streamflows and temperatures
Photo Credit: TJ Watt
A new study finds that forestry can significantly impact streamflows and temperatures. However, these effects vary and cannot be reliably predicted by easily measured watershed characteristics.
The study, published in Ecological Solutions and Evidence, was authored by Sean M. Naman, Kara J. Pitman, Dylan S. Cunningham, Anna Potapova, Shawn M. Chartrand, Matthew R. Sloat, and Jonathan W. Moore.
Background
Forestry is a prevalent activity in many regions of western North America, and many of these watersheds also support important salmon populations. As climate change warms water temperatures or alters flow regimes, there is a concern that forestry could also be contributing to these stressors.
There is a long history of studies using experimental forestry to understand its impacts. These studies involve harvesting one small catchment in a particular way and then comparing it to an unlogged catchment. These are called "paired-catchment" studies. This paper compiled and analyzed 50+ years of these paired catchment studies across the range of Pacific salmon in North America (Fig 1).
Figure 1. Map of paired catchment studies used in the analysis
Citation
Naman, S. M., Pitman, K. J., Cunningham, D. S., Potapova, A., Chartrand, S. M., Sloat, M. R., & Moore, J. W. (2024). Forestry impacts on stream flows and temperatures: A quantitative synthesis of paired catchment studies across the Pacific salmon range. Ecological Solutions and Evidence, 5, e12328.
Results and Implications
In most studies, forestry activities led to significant environmental changes: peak flows increased by approximately 20%, summer low flows decreased by around 25%, and summer temperatures rose by about 15% (Fig. 2). These stressors mirror the anticipated effects of climate change in many regions.
However, the responses were highly variable and unpredictable. The magnitude of the forestry impacts was not related to the watershed characteristics available for analysis, such as precipitation and underlying geology. Furthermore, the extent of the harvest, ranging from 5% to 100%, did not predictably mitigate the impacts, indicating that any level of forestry could have substantial effects on watersheds.
Thus, while forestry can have significant environmental impacts, these effects are broadly unpredictable without more detailed, watershed-specific information.