For decades, forest rules in Washington and Oregon have required fixed-width no-harvest buffers along some headwater streams. The assumption is simple: wider buffers always provide more shade, and more shade means cooler water.
But that’s not always true.
Tree height, slope, valley shape, and the path of the sun all determine whether a tree is actually shading the water. A fixed-width approach doesn’t account for these differences—meaning landowners may leave trees that don’t shade the stream while being able to include trees that do in plans for future harvests.
The new study tested a different idea: What if we placed buffers where they actually block the sun, rather than where the rulebook says?
Introducing “Shadesheds”
Using modern lidar mapping, researchers identified the exact areas of forest—called “shadesheds”—that block midday sunlight during the warmest part of the year. They then designed Variable-Width Shade Buffers (VWSBs) that focused protection only on the parts of the riparian zone that provide meaningful shade.
The study authors compared their designed buffers to Washington’s existing one-size-fits-all Forest Practice Buffers (FPBs) across 19 headwater streams. The takeaway: performance-based buffers may outperform traditional one-size-fits-all rules.
The key findings offer regulators a new way to protect the environment without doing unnecessary harm:
- Smarter buffer placement = better shade — VWSBs provided equal or better effective shade than traditional fixed buffers at most sites. In many cases, they achieved high shade levels with less total timber retained because the buffer followed the actual solar geometry, not a uniform distance.
- VWSBs are more efficient — The study found that VWSBs produced more shade per acre of buffer—a direct measure of efficiency. Traditional buffers often leave trees in spots that don’t shade the water, while missing areas that do.
- Stream temperatures didn’t worsen — The most important question: do these smarter, variable-width buffers keep streams from warming? According to the authors, yes.Across all sites, there was no detectable difference in stream temperature outcomes between VWSBs and traditional buffers. Temperature responses were highly variable and influenced by many natural factors, but VWSBs performed just as well as the standard approach.
- Local conditions matter — Stream orientation, surface flow, understory shrubs, and groundwater all played roles in how water temperature changed after harvest. This helps explain why fixed-width rules don’t always match real-world conditions.
New Tool for Modern Forestry?
For landowners, tribes, agencies, and conservation groups, the study could open new discussion about how Washington’s forest practices can evolve to fix the inefficiencies of the current one-size-fits-all approach. The old ways may have been the best method we had last century, but we can embrace what science and new technology allows today.
Finding a way to secure greater protections for water temperature without weakening working forests—a critical partner in efforts to fight climate change and reduce catastrophic wildfire—is a quest worth pursuing.