Across these three zones, the data suggest that opening canopy gaps can increase total snow storage on the landscape. However, to gain a duration effect, forest management should be paired with other established restoration strategies to hold water on the landscape longer. These restoration strategies could include floodplain reconnection, wet meadow restoration, and reversal of stream incision. But we also wondered whether we could acheive increased snowpack duration effects by placing forest thinning treatments on shady, north-facing slopes.
Taking the Study to Cle Elum Ridge
To drill into this question, we took the study to Cle Elum Ridge, part of TNC’s 48,000-acre forest protection project at the headwaters of the Yakima Basin in the Central Cascades. Using the same experimental design described earlier, we compared forest-snow interactions between north and south-facing slopes. On the north side of the ridge, snowpack measured 2.9x deeper in gaps compared to forested plots, and lasted 12-30 days longer in the gap. In contrast, snowpack on the south side gaps measured 1.5x deeper than forested plots, but only lasted 2 days longer. Our data shows that on opposites sides of the ridge, lies the potential for water storage.
While twelve more days of cold water may not sound like much, nature works at multiple scales. The difference of a few days to weeks of cold spring meltwater is critical for out-migrating salmonids. In the Yakima Basin, juvenile Chinook leaving the upper watersheds past May simply don’t make it through the lower river anymore. Over 95% of them die due to high temperatures, slow water movement, and predation.
Scaling Up: Site Specific to Landscape Scale Investigations
As we developed our snowpack study, the Tapash Forest Collaborative’s leadership team, who seeks to improve ecosystem health and natural functions of the landscape across ownership in central Washington, helped us narrow the objectives. They wanted to know how different levels of forest thinning affect snowpack storage and duration, and whether our research team could quantify the amount of snowpack storage gained through specific thinning treatments.
