King County begins another "gap treatment" Project in Cougar Mountain Wildland Park

This spring, King County is planning another “gap treatment” project in Cougar Mountain Regional Wildland Park. This involves cutting down some broadleaf trees like red alder and bigleaf maple at seven different sites in the park to make room for new conifer trees. This project won’t affect any trails, but you may be able to see some of this work being done from trails within the park. 

Why do we need gaps in the forest canopy? 

As you may have noticed on your hikes around Cougar Mountain, many of the forests there are dominated by broadleaf trees such as red alder and bigleaf maple. While these trees are wonderful to see and do play an important part in our forest ecosystems, their abundance doesn’t reflect the composition of our forests historically. Before many of these forests were clear-cut, mined, and abandoned, they were dominated by conifers such as Douglas-fir, Western Hemlock, and Cedar trees. According to King County “By creating these conifer-dominated patches in the forest, we increase species diversity and restore the ecologically important role these long-lived conifers provide.” 

Why are conifers so important to our forests? 

Conifers live much longer than most broadleaf trees. Trees like Douglas-fir can live anywhere from 500 to 1,000 years! In contrast, the typical lifespan of a red alder is about 100 years, and many of the red alders that exist in Cougar Mountain Wildland Park are already reaching the end of that lifespan. By planting conifers, we can increase the resilience of our forests over time. Additionally, climate change predictions show hotter, drier summers ahead. Broadleaf trees are less well-adapted to dry climates and may suffer in the future, whereas conifers could provide some stability in forests. Finally, conifers store more carbon than broadleaf trees. According to King County “These projects increase forest carbon storage over time compared to a no-action management approach – the large and fast-growing conifers more than recapture the carbon that is lost by the dead and dying red alder.” 

What steps are involved in this project? 

The county will start by cutting down some of the broadleaf trees across seven sites in Cougar Mountain Wildland Park. The total project area will include 11 acres, but not every broadleaf tree within that area will be cut down. Between one and five healthy overstory red alder or bigleaf maple per acre will be retained, as well as all conifers, and several trees may also be girdled to slowly create snags for wildlife. The county will then plant a mixture of native conifers including Douglas-fir, western redcedar, and grand fir. They will maintain the planted trees throughout 2021 and 2022 by removing vegetation that threatens the seedlings and invasive plant removal. 

If you would like to learn more about how King County is building healthy forests please visit: https://www.kingcounty.gov/services/parks-recreation/parks/parks-and-natural-lands/natural-lands/forest-stewardship.aspx