Global climate change is now impacting the Puget Sound region’s native forests and plant communities with changing temperatures and precipitation regimes that is making them vulnerable to disease and die-offs. Hotter and longer droughts are already occurring, with diebacks of Lodgepole and Ponderosa pine, Oregon ash, Western redcedar sword fern, and Bigleaf maple.

• Average summer temperatures are projected increase by +4.7°F - 16.7°F by 2080. Summer temperature highs are also projected to increase, with +8 days of above 90°F, with temperatures increasing +12.03°F.  
• The Puget Sound region is projected to shift from USDA Plant Hardiness Zones 8 to Zone 9 completely, and from Heat Zone 2 to Heat Zone 6.
• Higher temperatures cause native plants to experience more heat-related stress. Heat stress causes higher water demand, a situation made worse by longer droughts.
• Higher atmospheric carbon dioxide (CO2) levels promote the growth of invasive plant species, decreasing the space needed to support natural areas.

How will this affect native plants?

Each native plant species has a natural range. Within that natural range, there are specific habitats that contain the ideal combination of growing conditions for that species.  Accordingly, the geographic range over which a native species' original growing conditions occur is moving. Native plant species will go extinct if they do not acclimate, adapt or move. This potential loss of plant species and communities will cause a cascade of affects to entire ecosystems of soils, insects, fish, birds, animals, and human communities.

How can we adapt to climate change?

Identifying native plant species that have a high probability of survival under current and future projected climate change conditions can help ecosystem managers, ecologists, homeowners, and nurseries to select, plant, and propagate climate-adapted species to preserve local ecosystems.

The human-assisted movement of species in response to climate change is referred to as assisted migration. This approach is being used by the US Forest Service, Park Service, and Bureau of Land Management to conserve tree species and replace plant species with genetic strains or species that are climate adapted. Climate-smart native plants are native species adapted to both current and future hardiness zones and can be used to create climate-smart gardens and landscapes.

What is King County doing?

King County is expanding the list of native plants to include plant species that have a high probability of survival under current and future projected climate change conditions - species that are native to warmer and drier northwest regional landscapes. These climate-adapted plants are referred to as ‘climate smart’ plants. These are plant species that are presently or prehistorically found within our Puget Trough ecoregion, and neighboring ecoregions, including the Willamette Valley, Georgia Basin, and Columbia Basin. These ecoregions influence and share many aspects of climate, geology, landforms, and native species with each other. The new list also includes common native species that were left off prior versions of our native plant list, and species from the prehistoric, paleo record that could be reintroduced to the region. Below you will find questions about our proposed additions. 

Once we have completed this peer review, we will finalize the native plant list, adopt into King County Code and incorporate it into the Northwest Native Plant Guide.

Thank you and please be in touch with any questions!